European Journal of Inorganic Chemistry

Current research reports and chronological list of recent articles.

The scientific European Journal of Inorganic Chemistry - EurJIC - is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.

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European Journal of Inorganic Chemistry - Abstracts

Back Cover: Low-Coordinate Phosphorus Compounds (Eur. J. Inorg. Chem. 5/2016)

The back cover picture shows the synthesis of dinuclear copper(I) halide complexes from a new diphenylphosphinite phosphinine as chelating ligand and simple CuI halides. Remarkably, it is the phosphorus center, and not the halide, that bridges the Cu centers. These complexes show phosphorescence in the range 658–702 nm in the solid state at room temperature. The emission can be tuned by changing the terminal halide ligand. Details are discussed in the Communication by Z. Li, H.-J. Grützmacher et al. on p. 633 ff. For more on the story behind the cover research, see the Cover Profile.
Datum: 12.02.2016

Synthesis and Photoluminescence Properties of CuI Complexes with Chelating Phosphinito Phosphinine Ligands

Invited for the cover of this issue are the groups of Hansjörg Grützmacher, ETH Zurich, Switzerland, and Zhongshu Li, Sun Yat-Sen University, Guangzhou, China. The cover image shows the synthesis of dinuclear copper(I) halide complexes from a new diphenylphosphinite phosphinine as chelating ligand and simple CuI halides. The most remarkable aspect is that the low-coordinate phosphorus center of the phosphinine ring resides in the bridging position between the two Cu centers...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 633 ff.
Datum: 12.02.2016

The Route to Phosphabenzene and Beyond

This article presents the background of the author's synthesis of phosphabenzene in 1971. It also expands to tell the story behind the syntheses of the heavier group 15 heterobenzenes: arsabenzene, stibabenzene, and bismabenzene, which were prepared nearly at the same time and by a largely similar route. This essay recalls the author's syntheses of phosphabenzene, arsabenzene, stibabenzene, and bismabenzene in 1971 and 1972.
Datum: 12.02.2016

Spotlights on our sister journals: Eur. J. Inorg. Chem. 5/2016

Datum: 12.02.2016

Cover Picture: Low-Coordinate Phosphorus Compounds (Eur. J. Inorg. Chem. 5/2016)

The cover picture, designed by Guest Editor Christian Müller, shows the original paper published in Angew. Chemie in 1966 of the synthesis of the first low-coordinate organophosphorus compound, 2,4,6-triphenylphosphabenzene, by Gottfried Märkl. The structure of the stable yellow crystalline compound is also depicted. This communication was central in changing the way the bonding around phosphorus atoms was viewed, and the demonstration that hybridization was possible for phosphorus led to many reports on formally sp2-hybridized phosphorus(III) compounds with significantly different properties from those of classical trivalent phosphorus species.
Datum: 12.02.2016

Low-Coordinate Phosphorus Compounds

Guest Editor Christian M�ller presents an overview of the papers in this Cluster Issue commemorating the synthesis of the first low-coordinate organophosphorus compound in 1966. Guest Editor Christian M�ller presents an overview of the papers in this Cluster Issue on the occasion of the fiftieth anniversary of the synthesis of the first low-coordinate organophosphorus compound by Gottfried M�rkl in 1966.
Datum: 12.02.2016

Low-Coordinate Phosphorus Chemistry Has Come a Long Way

Editor Karen Hindson highlights the importance of low-coordinate phosphorus chemistry and tells the story of this Cluster Issue on the fiftieth anniversary of the synthesis of the first low-coordinate phosphorus compound. Editor Karen Hindson introduces this Cluster Issue on low-coordinate phosphorus compounds including papers highlighting the present state of the field after fifty years of development since the synthesis of the first low-coordinate phosphorus compound in 1966.
Datum: 12.02.2016

Inside Cover: Low-Coordinate Phosphorus Compounds (Eur. J. Inorg. Chem. 5/2016)

The inside cover picture shows the attempt to stabilize the highly reactive tetramesityltetraphosphanediide anion (P4Mes42–, Mes = 2,4,6-Me3C6H2) by adduct formation with an N-heterocyclic carbene (NHC). However, rather than forming the expected stable adduct, the attack of the NHCs rips the tetraphosphanediide chain apart to produce two neutral carbene–phosphinidenes and a P2Mes22– dianion, which is not “trapped” with NHC. Details are discussed in the Communication by E. Hey-Hawkins et al. on p. 620 ff.
Datum: 12.02.2016

M-Doped TiO2 and TiO2–MxOy Mixed Oxides (M = V, Bi, W) by Reactive Mineralization of Cellulose – Evaluation of Their Photocatalytic Activity

M-doped TiO2 and mixed oxides MxOy–TiO2 (M = V, Bi, W) were synthesized by the reactive mineralization of ash-free filter paper under anhydrous conditions. Mixtures of metal chlorides (TiCl4 with VOCl3, WCl6, or BiCl3) were reacted directly with cellulose, and three different Ti/M atomic ratios were used (99, 19, and 9). The resulting materials consist of original nanoflower assemblies of needle-shaped primary particles. Their physicochemical characteristics were investigated by various techniques (X-ray diffraction, diffuse-reflectance UV/Vis spectroscopy, electron microscopy, and elemental analysis). The incorporation of the doping metal or the formation of mixture of oxides with TiO2 (WO3, Bi2O3) depends on the metal and the proportions used. The photocatalytic activities of the materials were tested for the degradation of phenol. The vanadium-doped materials exhibit true solid-solution formation and their band gaps shift into the visible range. M-doped TiO2 and mixed oxides MxOy–TiO2 (M = V, Bi, W) are synthesized by the reactions of ash-free filter paper with mixtures of metal chlorides (TiCl4 + 1–10 % VOCl3, WCl6, or BiCl3). The resulting materials have nanoflowers of needle-shaped primary particles and are characterized by X-ray diffraction, diffuse-reflectance UV/Vis spectroscopy, electron microscopy, and elemental analysis.
Datum: 12.02.2016

Switchable Polymerization of Norbornene Derivatives by a Ferrocene-Palladium(II) Heteroscorpionate Complex

The ferrocene-chelating heteroscorpionate complex [(fc(PPh2){BH{(3,5-Me)2pz}2})PdMe] {(fcP,B)PdMe, fc = 1,1′-ferrocenediyl, pz = pyrazole} catalyzes the addition polymerization of norbornene and norbornene derivatives upon oxidation with [AcFc][BArF] {acetyl ferrocenium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate}. In situ reduction of [(fcP,B)PdMe][BArF] in the presence of a substituted norbornene results in significant decrease of catalytic activity. Addition of one equivalent of oxidant restores the activity. A cationic ferrocene-chelating heteroscorpionate methylpalladium complex catalyzes the addition polymerization of norbornene and norbornene derivatives. Redox switchable polymerization of these monomers was also accomplished.
Datum: 12.02.2016

Transition Metal Mediated C–H Activation and Functionalization: The Role of Poly(pyrazolyl)borate and Poly(pyrazolyl)alkane Ligands

The emergence of hydridotris(pyrazolyl)borate (Tp) and related ligands has had a substantial influence in the field of organometallic chemistry with regards to C–H activation. The electronic and structural properties of Tp and related ligands, such as poly(pyrazolyl)alkane ligands, play an important role in the ability of several transition metal complexes to mediate C–H activation and functionalization. Herein, several studies of stoichiometric and catalytic C–H activation by platinum group metals are reviewed. This microreview presents work surrounding the development and study of Tp-supported platinum group metal complexes for stoichiometric and catalytic C–H bond activation. From κ2- and κ3-coordination modes to increased sterics to electronic parameters, Tp and related ligands have played an important role in the observed reactivity of Ru, Rh and Pt-mediated C–H bond activation reactions.
Datum: 12.02.2016

Mixed Alkyl-Perfluoroalkyl Silver Scorpionates: Synthesis, X-ray Structures and Stabilizing Substituent Effects

We report the synthesis, spectroscopy and X-ray structural characterization of seven new mixed alkyl-perfluoroalkyl silver tris(pyrazolyl)borate complexes with the general formula Tp R F,CH 3Ag, where RF = CF3 or C2F5. The metal is partly encapsulated in a fluorine-rich environment and exhibits high Lewis acidity, allowing additional coordination by toluene (Tol), triphenylphosphine (PPh3), methyldiphenylphosphine (PMePh2) and triphenylphosphine oxide (OPPh3). A single-crystal X-ray analysis of the new data proposes a structural model that predicts interatomic distances and may rationalize the relative stability of members of this class of compounds. The electronic and steric effects of Tp substituents, combined with those of additional ligands, can lead to remarkably stable compounds, both in solution and the solid state, even when an ion particularly prone to reduction, such as silver(I), is involved. Seven new mixed alkyl-perfluoroalkyl silver tris(pyrazolyl)borate complexes are reported and structurally characterized. Single-crystal X-ray analysis defines a structural model that predicts interatomic distances and rationalizes the relative stability of members of this class of compounds.
Datum: 12.02.2016

How Hydrogen Bonds Affect Reactivity and Intervalence Charge Transfer in Ferrocenium-Phenolate Radicals

Datum: 12.02.2016

Three-Dimensional Electrocatalysts for Sustainable Water Splitting Reactions

Development of catalysts with high activity and durability is essential for the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) of water splitting. Three-dimensional catalysts have large surface areas and good mechanical and antipoisoning properties and can directly act as working electrodes; these are especially important factors from the point of view of practical applications. Here we review recent significant progress in the field of three-dimensional catalysts for water splitting. Various three-dimensional catalysts that can be applied in electrocatalytic water splitting are presented. The fabricating methods, electrocatalytic performances, and the catalytic mechanisms of these catalysts are introduced. Lastly, the major challenges in this particular field and their prospective solutions are also discussed. Three-dimensional (3D) electrocatalysts have captured much attention in the field of water splitting due to their unique properties of high surface area and good mechanical strength. This review presents the general synthesis method and the electrocatalytic performances of different kinds of 3D catalysts in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER).
Datum: 10.02.2016

Extremely Low Temperature Crystallization in the A2M3O12 Family of Negative Thermal Expansion Materials

A2M3O12 materials (A = Al, Sc, Fe, In, Ga, Y; M = Mo, W) were synthesized using the non-hydrolytic sol-gel process. In contrast to previous studies, in which amorphous materials were recovered that required heating to 500–700 °C to induce crystallization, several compounds could be crystallized in a temperature range compatible with low temperature processing of devices and composites. Under certain reaction conditions, crystalline Sc2Mo3O12, Fe2Mo3O12, and In2Mo3O12 were obtained at temperatures as low as 230 °C. This may allow use of these materials for in-situ composite formation, which could result in new practical applications. Under optimized reaction conditions, the non-hydrolytic sol-gel process can be used to obtain crystalline Sc2Mo3O12, Fe2Mo3O12, and In2Mo3O12 after heating at temperatures as low as 230 °C. This may allow use of these materials during in-situ composite preparation methods.
Datum: 10.02.2016

Isolable Ethylene Complexes of Copper(I), Silver(I), and Gold(I) Supported by Fluorinated Scorpionates [HB{3-(CF3),5-(CH3)Pz}3]– and [HB{3-(CF3),5-(Ph)Pz}3]–

The group 11 metal adducts [HB{3-(CF3),5-(CH3)Pz}3]M(C2H4) (M = Au, Ag, and Cu; Pz = pyrazolyl) have been synthesized via a metathesis process using [HB{3-(CF3),5-(CH3)Pz}3]Na and CF3SO3Cu, CF3SO3Ag, AuCl and ethylene. The related [HB{3-(CF3),5-(Ph)Pz}3]Ag(C2H4) has also been synthesized using [HB{3-(CF3),5-(Ph)Pz}3]Na(THF), CF3SO3Ag and ethylene. These group 11 metal ethylene complexes are white solids and form colorless crystals. They have been characterized by NMR spectroscopy and X-ray crystallography. The gold-ethylene adduct [HB{3-(CF3),5-(CH3)Pz}3]Au(C2H4) shows large upfield NMR shifts of the ethylene proton and carbon signals relative to the corresponding peaks of the free ethylene, indicating relatively high Auethylene backbonding. NMR chemical shift data suggest that the silver complexes of both the tris(pyrazolyl)borate ligands [HB{3-(CF3),5-(CH3)Pz}3]– and [HB{3-(CF3),5-(Ph)Pz}3]– exhibit the weakest interaction with ethylene as compared to the respective copper and gold complexes. X-ray crystal structures reveal that the gold atom in [HB{3-(CF3),5-(CH3)Pz}3]Au(C2H4) binds to scorpionate in κ2-fashion while the related silver adduct features a κ3-bonded scorpionate. [HB{3-(CF3),5-(CH3)Pz}3]Cu(C2H4) has a scorpionate that binds to copper with two short Cu–N bonds and one long Cu–N distance. Partially fluorinated scorpionate [HB{3-(CF3),5-(CH3)Pz}3]– allows the stabilization of molecules with gold(I), silver(I) and copper(I) ethylene adducts. Related adducts supported by [HB{3-(CF3),5-(CH3)Pz}3]– are also included for comparisons. Notable differences exist in scorpionate modes of coordination and ethylene carbon chemical shift values.
Datum: 09.02.2016

Syntheses, Crystal Structures, NMR Spectroscopy, and Vibrational Spectroscopy of Sr(PO3F)·H2O and Sr(PO3F)

Single crystals of Sr(PO3F)·H2O {P21/c, Z = 4, a = 7.4844(2) Å, b = 7.0793(2) Å, c = 8.4265(2) Å, β = 108.696(1)°, V = 422.91(2) Å3, 2391 Fo2, 70 parameters, R1[F2 > 2σ(F2)] = 0.036; wR2(F2 all) = 0.049, S = 1.054} were grown from an aqueous solution by a metathesis reaction. The structure comprises [SrO8] polyhedra and PO3F tetrahedra that form a layered arrangement parallel to (100). The topotactic dehydration of this phase proceeds between 80 and 140 °C to afford Sr(PO3F). The monazite-type crystal structure of Sr(PO3F) was elucidated from the X-ray powder data by simulated annealing [P21/c, Z = 4, a = 6.71689(9) Å, b = 7.11774(11) Å, c = 8.66997(13) Å, β = 128.0063(7)°, V = 326.605(8) Å3, Rp = 0.010, Rwp = 0.015, RF = 0.030]. During dehydration, the structure of Sr(PO3F)·H2O collapses along [100] from a layered arrangement into a framework structure, accompanied by a change of the coordination number of the Sr2+ ions from eight to nine. The magic-angle spinning (MAS) NMR and vibrational spectroscopy data of both phases are discussed. The dehydration of Sr(PO3F)·H2O yields Sr(PO3F) by a topotactic reaction. The crystal structures of both solids were elucidated by X-ray diffraction methods, and the presence of P–F bonds was confirmed by magic-angle spinning (MAS) NMR and IR spectroscopy.
Datum: 08.02.2016

Hydroelementation of Unsaturated C–C Bonds Catalyzed by Metal Scorpionate Complexes

Tridentate scorpionate ligands have a rich history in coordination chemistry. In the past two decades, metal complexes bearing scorpionate ligands have found increasing utility as catalysts for a variety of useful transformations. This microreview focuses on the utility of scorpionate ligands in hydroelementation of carbon–carbon unsaturated bonds, focusing specifically on hydrothiolation, hydroamination, hydroalkoxylation and hydrophosphinylation of alkenes and alkynes. In each example, the solid phase and solution phase coordination and fluxionality of the scorpionate ligand will be discussed. A review of recent advances in hydroelementation (E = S, N, O, P) of alkenes and alkynes catalyzed by metal complexes bearing scorpionate-type ligands.
Datum: 05.02.2016

Binary B4S4 Rhombic Clusters as Promising Inorganic Ligands for ­Triple-Decker Sandwich Complexes

Designing new forms of ligands and their sandwich-type analogs is the beginning of building multidecker metallic sandwich clusters and their infinite one-dimensional molecular wires. Here, we report on two binary B–S clusters: C2v B4S4 (1, 1A1) and D2h B4S4– (2, 2B2u) with rhombic B2S2 as the core are their global minimum structures based upon global searches and electronic structure calculations at the B3LYP and coupled-cluster theory [CCSD(T)] levels. The global-minimum structures 1 and 2 can be formulated as B2S2(BS)2 and feature B2S2 four-membered rings as the core, with two –BS terminal groups attached terminally, closely resembling B2S2H2 with a rhombic B2S2 core and obtainable from the latter by isovalent BS/H substitution. Bonding analyses reveal a 4c–4e o-bond in C2v B4S4 (1, 1A1), which is 4π systems in the nonbonding/bonding combination, in contrast to the antibonding/bonding combination in a classical 4π antiaromatic hydrocarbon such as cyclobutadiene (C4H4). The electronic properties of the global-minimum 1 and 2 clusters are predicted. C2v B4S4 (1, 1A1) is predicted to be effective as an inorganic ligand to form triple-decker sandwich-type transition-metal complexes, such as D2h (B4S4)3M2 (M = Ni, Pd, and Pt). These complexes, considering the formation energies, are found to be particularly stable. The sandwich structural pattern developed in this work expands the transition-metal complexes by introducing inorganic C2v B4S4 (1, 1A1) into traditional triple-decker sandwich structures and may be extended to form one-dimensional transition-metal sandwich polymers [M(B4S4)]∞ (M = Ni, Pd, and Pt). The binary B4S4 rhombic cluster possesses a four-membered heteroatomic ring with 4π electrons in a nonbonding/bonding combination, differing from cyclobutadiene. B4S4 (C2v 1A1) is predicted to be an effective inorganic ligand to form triple-decker sandwich-type transition-metal complexes, such as D2h (B4S4)3M2 (M = Ni, Pd, and Pt).
Datum: 05.02.2016

Conformational Analysis of P,N-Containing Eight-Membered Heterocycles and Their Pt/Ni Complexes in Solution

In solution, 1,5-diaza-3,7-diphosphacyclooctanes (PR2NR′2) are in equilibrium between the crown (CW; major) and chair–boat (CB; minor) forms. Aromatic substituent at the nitrogen atom shifts the equilibrium in favor of the CW form. [Pt(PR2NR′2)]Cl2 complexes exist in solution in the CB (CB*) conformation irrespective of the substituent at the heteroatoms. Aromatic substituents on N notably decrease the barrier of CB–CB* conformational exchange. Biligand complexes ([M(PR2NR′2)2]2+, M = Pt, Ni) are in CBCB1 conformation with distortion of the metal coordination plane. The CBCB1 form is in degenerate exchange with the CBCB1* form. In general, distortion of the metal coordination plane and the intramolecular exchange barriers are higher in Ni complexes than in Pt ones. An Ar group at the nitrogen atom increases the heterocycle interconversion rate. Bulky P-substituents increase the distortion of the metal coordination plane and slow down its “twisting” rate. Counterions with stronger coordinating ability increase the barriers of intramolecular conversion. Biligand complexes ([M(PR2NR′2)2]2+, M = Pt, Ni) are in CBCB1 conformation with distortion of the metal coordination plane. Ni complexes have higher distortion and intramolecular exchange barriers than Pt complexes. Bulky P-substituents increase the distortion of the coordination plane and slow down its “twisting” rate. The counterion type also affects the structure and dynamics of these complexes.
Datum: 05.02.2016

Synthesis and Charge–Discharge Properties of Organometallic Co­polymers of Ferrocene and Triphen­ylamine as Cathode Active Materials for Organic-Battery Applications

Two new organometallic copolymers (PVFVM1 and PVFVM1-1) bearing different molar ratios of ferrocene and triphenylamine pendants were successfully designed and synthesized as cathode active materials for organic-battery applications. Their structural and thermal characteristics were determined by 1H NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, size exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Cyclic voltammograms of the as-prepared polymers show that the electrochemical reactions of the ferrocene and triphenylamine moieties are reversible after the first cycle. A composite electrode based on copolymer PVFVM1 exhibits an initial specific discharge capacity of 102 mA h g–1, which corresponds to 98 % of its theoretical capacity (104 mA h g–1). The cycle endurances for both polymers have been evaluated for over 50 cycles. Our results show that both copolymers are good candidates as a new class of cathode active materials and charge-storage materials for rechargeable batteries. Copolymers of ferrocene and triphenylamine (PVFVM1 and PVFVM1-1) show electrochemical characteristics of the ferrocene and triphenylamine pendants with multiple redox waves. PVFVM1 exhibits a discharge capacity of 102 mA h g–1 at 10 C, which corresponds to 98 % of its theoretical capacity.
Datum: 05.02.2016

Sr2Pd4Al5: Synthesis, Crystal and Electronic Structures, and Chemical Bonding of a Polar Intermetallic Compound

The new intermetallic compound Sr2Pd4Al5 was prepared from the elements by reaction in niobium ampoules. The structure was refined from single-crystal data, which indicate the formation of a new structure type in the orthorhombic crystal system [a = 1814.49(10), b = 431.64(4), c = 1102.47(4) pm] with space group Pnma (wR2 = 0.0251, 1666 F2 values, 68 parameters). Full ordering of the transition-metal and aluminum sites was observed. The compound can be described as a polar intermetallic phase with a polyanionic [Pd4Al5]δ– network; however, a quite unique bonding situation was found within this framework. In addition to the usual Pd–Al bonding, significant contributions to the stability of the framework caused by homoatomic Pd–Pd and Al–Al interactions can also be found. Structural relaxation confirmed the electronic stability and predicted the compound to be a metallic conductor. Sr2Pd4Al5 crystallizes in a new structure type that exhibits an interesting bonding situation within the polyanionic [Pd4Al5]δ– framework. DFT calculations confirm the crystallographically observed bonding situations and that the compound should be considered polar intermetallic since Sr transfers its electrons mainly onto the palladium atoms.
Datum: 05.02.2016

Photoinduced and Self-Activated Nuclease Activity of Copper(II) Complexes with N-(Quinolin-8-yl)quin­olin-8-sulfonamide – DNA and Bovine Serum Albumin Binding

Two CuII complexes with a new quinoline sulfonamide derivative and phenanthroline (phen), [Cu(QSQ)(phen)]ClO4·0.5H2O (1) and [Cu(QSQ)(phen)(H2O)]ClO4 (2) [HQSQ = N-(quinolin-8-yl)quinolin-8-sulfonamide], have been synthesized and physicochemically characterized. Single-crystal X-ray diffraction studies have revealed a highly distorted trigonal-bipyramidal structure for 1 (τ = 0.68) and an almost perfect trigonal-bipyramidal geometry for 2 (τ = 0.92). DNA binding studies, which were performed by thermal denaturation, viscometry, fluorescence spectroscopy, and cyclic voltammetry, indicated a partial intercalation of 1 with Kapp = 2.45 × 106 M–1. The nuclease activity of 1 was investigated upon photoirradiation, with ascorbate/H2O2 as the activating agent, and also in the absence of any external reagent. In all cases, 1 was able to perform DNA cleavage, and its nuclease efficiency varied in the order ascorbate/H2O2 > photoirradiation > without external cofactors. Mechanistic investigations suggest an oxidative cleavage of DNA involving reactive oxygen species (ROS). The protein binding ability of 1 was also studied with bovine serum albumin (BSA) as a model protein. [Cu(QSQ)(phen)]ClO4·0.5H2O (1) and [Cu(QSQ)(phen)(H2O)]ClO4 [2; phen = phenanthroline, HQSQ = N-(quinolin-8-yl)quinolin-8-sulfonamide] are synthesized and physicochemically characterized. Compound 1 performs oxidative DNA cleavage upon photoirradiation in the presence of ascorbate/H2O2 and, interestingly, in the absence of any external reagent.
Datum: 05.02.2016

Gold-Mediated Isomerization of ­Cyclooctyne to Ring Fused Olefinic Bicycles

Isomerization reactions of cyclooctyne mediated by N-heterocyclic carbene supported gold(I) leading to ring-contraction and the formation of 5/5-fused bicyclic alkenes have been observed. Isolation and complete characterization, including X-ray structural data of the cationic gold(I) complexes featuring the precursor alkyne and the product alkenes are also described. Gold catalyzes the isomerization of cyclooctyne leading to alkenes featuring two fused five-membered rings.
Datum: 05.02.2016

Mechanism and Kinetics of Oligosilsesquioxane Growth in the In Situ Water Production Sol–Gel Route: Dependence on Water Availability

Thiol-functionalized nanobuilding blocks (NBBs) were synthesized from 3-mercaptopropyltrimethoxysilane by using the in situ water production (ISWP) process in which the water needed to hydrolyze the precursor was provided by means of an esterification reaction. In the present study the reaction between 1-propanol and chloroacetic acid was used. Whereas the growth of the Si oligomers was followed at room temperature and 100 °C using 1D 29Si and 2D 1H–29Si heteronuclear single quantum correlation (HSQC) NMR spectroscopic experiments, the amount of water delivered along the process was followed by means of 1H NMR spectroscopy. The results show a good correlation between the evolution of the degree of condensation and the amount of water produced in situ. They also point to the preferential formation of cagelike structures and the narrowing of the species distribution over long reaction times. The average size of the growing oligomers was estimated from their diffusion coefficient, which was measured by means of 1H diffusion-ordered NMR spectroscopy (DOSY NMR). Like gel permeation chromatography, DOSY NNR showed a plateau between 70 to 100 hours in the growth of the oligomers, a time at which, according to 29Si NMR spectroscopy, the well-defined octakis(3-mercaptopropylsilsesquioxane) is the major species. Small thiol-functionalized oligosilsesquioxanes were prepared by the in situ water production (ISWP) process in which water was homogenously generated by an esterification reaction. Manipulation of the temperature allowed the water production kinetics to be controlled, which played a major role on the degree of condensation (DOC) of the formed nanobuilding blocks.
Datum: 05.02.2016

Gold Nanoparticle@Polyhedral Oligomeric Silsesquioxane Hybrid Scaffolds in Microfluidic Format – Highly Efficient and Green Catalytic Platforms

We report on the preparation of new hybrid organic–inorganic multiporous monolithic capillary columns carrying gold nanoparticles of 5, 10, 50, and 100 nm size and their use as flow-through catalytic platforms for aqueous liquid-phase reduction reactions. We found that the flow-through performance of the reactors depends not only on the size of the gold nanoparticles but also on the interplay of the pore size of the scaffolds and the catalytically available gold surface within the system, that is, loading an increased number of gold nanoparticles of smaller size does not necessarily result in strictly improved performance. This indicates the importance of the interplay between the nanopore size of the scaffolds and the catalytically active gold surface existing within the system. Demonstration of the highly efficient catalytic flow-through operation within seconds and the repeated use of the reactors without loss of performance indicates their excellent suitability as microfluidic device elements. Hybrid organic–inorganic porous monolithic materials were prepared in situ in small conduits. Their internal structure is decorated with gold nanoparticles anchored by pendant thiol groups through thiol–gold interactions. The materials are efficient catalysts, and their repeated use under continuous flow catalysis conditions results in no loss of performance, which indicates their robustness.
Datum: 05.02.2016

Thermoelectric Properties of Ni0.05Mo3Sb5.4Te1.6 with Embedded SiC and Al2O3 Nanoparticles

First, a large sample of Ni0.05Mo3Sb5.4Te1.6 was prepared by heating the elements in the stoichiometric ratio. β-SiC nanoparticles were added in volume fractions, f, of 0.01, 0.02, and 0.034 to three different portions of the material, and a portion without SiC nanoparticles was retained as a reference. All four samples were subjected to consolidation by hot-pressing. Furthermore, Al2O3 nanoparticles were added in volume fractions of f = 0.01, 0.0216, and 0.0325 to three other portions, again retaining a fourth protion as reference. These four samples were consolidated by spark-plasma sintering. The thermoelectric transport properties of these composites were characterized from 325 to 740 K. For the sample with 0.01 volume fraction of SiC, there was an enhancement in figure of merit by 18 % compared with the reference sample, mainly due to an 18 % reduced thermal conductivity. The 9 % reduction in thermal conductivity of the sample with 0.01 volume fraction of Al2O3 was not enough to compensate the loss in the power factor of 18 %, leading to a decrease in the figure of merit. Microstructural information obtained by SEM, TEM, and BET was used to elucidate the phase and transport properties. The spark-plasma-sintered bulk sample has a figure of merit that is 35 % higher than the bulk sample consolidated through hot-pressing. Nanocomposites of Ni0.05Mo3Sb5.4Te1.6 with embedded SiC and Al2O3 nanoparticles are introduced. The nanoadditions lower the thermal and electrical conductivities to different extents, ultimately resulting in enhanced thermoelectric performance (ZT) on addition of small amounts of SiC. A more substantial enhancement was achievement by spark-plasma-sintering instead of hot-pressing.
Datum: 03.02.2016

Enhancing Reactivity of Directly ­Observable B–H–Pt Interactions through Conformational Rigidity

We report for the first time the direct syntheses of trimethylplatinum(IV) complexes supported by bis(pyrazolyl)dihydridoborate (Bp) and bis(3,5-dimethylpyrazolyl)dihydridoborate (Bp*) ligands from the corresponding dimethylplatinum(II) complexes. X-ray crystallographic and multinuclear NMR characterization of the trimethylplatinum(IV) complexes reveal agostic B–H–Pt interactions. Solid-state analysis reveals that BpPtIVMe3 adopts a dinuclear structure featuring an intermolecular B–H–Pt bridge, whereas Bp*PtIVMe3 adopts a mononuclear structure containing an intramolecular B–H–Pt bridge. Addition of acetonitrile leads to cleavage of the weakly coordinating B–H–Pt interactions, and in the case of Bp*PtIVMe3, leads to hydroboration of acetonitrile. The B–H fragment interacting with the PtIV center in Bp*PtIVMe3 was also found to react with methanol to form a methoxy-bridged complex. DFT calculations were employed to investigate the structural contributions to the difference in the reactivity of the Bp- and Bp*-supported complexes. Trimethylplatinum(IV) complexes featuring agostic B–H–Pt interactions supported by bis(pyrazolyl)borate (Bp) and bis(3,5-dimethylpyrazolyl)borate (Bp*) ligands show interesting structural differences both in solution and the solid state. These differences result in enhanced reactivity of the Bp* complexes towards hydroboration of acetonitrile and protonolysis with methanol.
Datum: 03.02.2016

Mimicry of the 2-His-1-Carboxylate Facial Triad Using Bulky N,N,O-Ligands: Non-Heme Iron Complexes Featuring a Single Facial Ligand and Easily Exchangeable Co-Ligands

Mononuclear iron(II) complexes with facially coordinating N,N,O-ligands were synthesized as accurate structural mimics of the 2-His-1-carboxylate facial triad found in mononuclear non-heme iron enzymes. Mimicking of the facial triad is achieved by designing sterically demanding ligands providing two histidine-like benzimidazole moieties and a coordinating carboxylate or ester moiety. The new methyl-substituted analogue of the bis(benzimidazolyl)propionate ligand, BMBMeIP and its ester analogue, BMBMeIPnPr are designed to prevent the formation of previously reported coordinatively saturated FeL2 type complexes. The crystal structure of [Fe(BMBMeIPnPr)(OTf)2] shows a facial N,N,O-coordination that is very similar to the structure of the enzyme active sites. Both [Fe(BMBMeIPnPr)(OTf)2] and [Fe(BMBMeIP)(OTf)(MeCN)n] catalyze the epoxidation of olefins using H2O2, reaching turnover numbers up to 5.8 per iron. These results represent the first examples of iron complexes bearing a single facial and rigid N,N,O-coordinating ligand and three readily available coordination sites showing catalytic activity in oxidation reactions. Mononuclear iron(II) complexes with a single facially coordinating N,N,O-ligand were synthesized as accurate structural mimics of the 2-His-1-carboxylate facial triad found in mononuclear non-heme iron enzymes. The new [FeLOTfn] complexes provide three readily available coordination sites and show catalytic activity in epoxidation reactions.
Datum: 02.02.2016

Two Green-Phosphorescent Iridium Complexes with 2-Phenylpyrimidine Derivatives and Tetraphenylimido­diphosphinate for Efficient Organic Light-Emitting Diodes

Two phosphorescent IrIII complexes Ir1 and Ir2 containing 5-fluoro-2-[4-(trifluoromethyl)phenyl]pyrimidine and 2-(3,4-difluorophenyl)-5-fluoropyrimidine as cyclometalated main ligand and tetraphenylimidodiphosphinate as ancillary ligand were synthesized. Ir1 was characterized by single-crystal X-ray crystallography. Ir1 and Ir2 show green emissions peaking at 527 and 513 nm, respectively. By using the two complexes as emitters, organic light-emitting diodes (OLEDs) with the structure of TAPC (1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane, 40 nm)/Ir1 or Ir2 (10 wt.-%):mCP (1,3-bis(9H-carbazol-9-yl)benzene, 20 nm)/TmPyPB (1,3,5-tris(m-pyrid-3-ylphenyl)benzene, 30 nm)/LiF (1 nm)/Al (100 nm) showed high performance with maximum current efficiencies as high as 81.91 or 71.17 cd A–1 and maximum external quantum efficiencies of 20.8 or 21.3 %, respectively. The low-efficiency roll-off ratios of the two devices suggest that the two complexes have potential applications in OLEDs. Organic light-emitting diodes (OLEDs) based on IrIII complexes containing pyrimidine derivatives as cyclometalated ligands and tetraphenylimidodiphosphinate as ancillary ligand exhibited maximum current efficiencies as high as 81.91 and 71.17 cd A–1 and maximum external quantum efficiencies of 20.8 and 21.3 %, respectively, with low-efficiency roll-off.
Datum: 02.02.2016

Mitochondria-Targeting Iron(III) Catecholates for Photoactivated Anticancer Activity under Red Light

Iron(III) catecholates [Fe(R′-bpa)(R-dopa)Cl] (1, 2) with a triphenylphosphonium (TPP) moiety, where R′-bpa is 2-(TPP-N,N-bis((pyridin-2-yl)methyl)ethanamine) chloride (TPPbpa) and R-dopa is 4-{2-[(anthracen-9-yl)methylamino]ethyl}benzene-1,2-diol (andopa, 1) or 4-{2-[(pyren-1-yl)-methylamino]ethyl}benzene-1,2-diol (pydopa, 2), were synthesized and their photocytotoxicity studied. Complexes 3 and 4 with [phenyl-N,N-bis(pyridin-2-yl)methyl]methanamine (phbpa) were used as controls. The catecholate complexes showed an absorption band near 720 nm. The 5e– paramagnetic complexes showed a FeIII/FeII irreversible response near –0.45 V and a quasi-reversible catechol/semiquinone couple near 0.5 V versus saturated calomel electrode (SCE) in DMF/0.1 M tetrabutylammonium perchlorate. They showed photocytotoxicity in red/visible light in HeLa, HaCaT, MCF-7, and A549 cells. Complexes 1 and 2 displayed mitochondrial localization, reactive oxygen species (ROS) generation under red light, and apoptotic cell death. Control complexes 3 and 4 exhibited uniform distribution throughout the cell. The complexes showed DNA photocleavage under red light (785 nm), forming hydroxyl radicals as the ROS. Iron(III) catecholates bearing anthracenyl or pyrenyl groups and a dipicolylamine base with a cationic triphenylphosphonium (TPP) moiety show remarkable photocytotoxicity under red light, mitochondrial localization, reactive oxygen species (ROS) generation, and apoptotic cell death. They showed significant DNA photocleavage activity under red light (785 nm), forming hydroxyl radicals as the ROS.
Datum: 02.02.2016

Bis(pyrazol-1-yl)(pyridin-x-yl)methane Ligands – Mono- or Ditopic Ligands in Complexes and Supramolecular Frameworks

Bis(pyrazol-1-yl)(pyridin-x-yl)methane ligands give rise to a rich variety of complexes with a wide range of transition metals. The derivatives with x = 2 act as monotopic and tripodal ligands. In the cases of ligands with x = 3 or 4, tripodal coordination is no longer possible and they generally behave as ditopic ligands that bridge two metal centres in cyclic dimers and trinuclear or polymeric species. The metal geometry has a clear influence on the type of compound formed. Ligands with x = 3 generate chiral cyclic dimers. Ligands that contain two bis(pyrazolyl)methane groups behave as ditopic, but they also act in a monotopic fashion in some cases. Analysis of the influence of some factors as the counteranion or the substituents on the ligand rings has been carried out. A two-step methodology starting from dimers and connectors was used to obtain egg-crate polymers or hexanuclear cyclic helicates. A comparative analysis of some parameters of the ligands has been performed. Bis(pyrazol-1-yl)(pyridin-x-yl)methane ligands give rise to a rich variety of complexes and supramolecular frameworks with a wide range of transition metals. With x = 2, the ligands behave as monotopic, usually with tripodal coordination, whereas with x = 3 or 4 they act as bridges, giving rise to polymers or dinuclear or trinuclear discrete species.
Datum: 01.02.2016

Activation of Heteroallenes COxS2–x (x = 0–2): Experimental and Theoretical Evidence of the Synthetic Versatility of a Bulky Guanidinato SmII Complex

A joint experimental/theoretical (DFT) study of the activation of heteroallenes COxS2–x (x = 0–2) by [Sm(Giso)2] {Giso– = [(ArN)2CNCy2]–, Cy = cyclohexyl, Ar = 2,6-diisopropylphenyl} is reported. All heteroallenes are reduced in a different manner. Indeed, while activation of CS2 yields a bimetallic CS2 coupled product through C–S bond formation, CO2 forms an oxalate complex through C–C bond formation. This subsequently undergoes CO2 insertion into one of its Sm–N bonds. Finally, COS activation is predicted to yield a dithiocarbonate complex, through the formation of an intermediate sulfido complex [(Giso)2Sm(µ-S)Sm(Giso)2]. Therefore, [Sm(Giso)2] is a very versatile reagent, since it is a rare example of a complex that allows formation of several activation products involving valence isoelectronic substrates. This is rationalized by DFT calculations, and the latter emphasizes both the lack of kinetic stability of CS vs. CO and the high thermodynamic stability of the oxalate. A combined experimental/DFT study of the activation of COxS2–x (x = 0–2) by [Sm(Giso)2] is reported. Activation of CS2 yields a bimetallic CS2 coupled product. CO2 forms an oxalate complex through C–C bond formation, which then undergoes CO2 insertion into one of its Sm–N bonds. COS activation is predicted to yield a dithiocarbonate complex, through the formation of an intermediate sulfido complex.
Datum: 01.02.2016

Dynamic Phosphonic Bridges in Aqueous Uranyl Clusters

The uranyl cage clusters (UO2)22(O2)15(PHO3)20(H2O)1026– (U22) and (UO2)28(O2)20(PHO3)24(H2O)1232– (U28) can be probed in aqueous solutions by using a combination of 1H Diffusion-Ordered Spectroscopy (DOSY) and 1H-31P Heteronuclear-Single Quantum Coherence (HSQC) spectroscopy. This class of clusters is ideal for 1H NMR analysis in D2O because of the covalent character of the H–P bond in the phosphonic bridges. 1H DOSY indicates that the clusters are stable in solution and provides hydrodynamic radii of 9.8 ± 0.4 Å for the U22 and 12.3 ± 0.5 Å for the U28 clusters. Furthermore, 1H-31P HSQC delivers unequivocal signal assignment for both nuclei, which enables solution dynamics to be monitored by variable-temperature experiments, and reveals the presence of phosphonic-bridge conformers. The results provide some of the first dynamic information about steady conformational changes in these enormous actinide macroions. The phosphonic bridges in the uranyl cage clusters U22 and U28 have been monitored in aqueous solutions using the unique combination of 1H DOSY and 1H-31P HSQC spectroscopy. The hydrodynamic radii of these clusters are measured to be 9.8 ± 0.4 Å (U22) and 12.3 ± 0.5 Å for the (U28) in D2O. Relating specific sites in the structures of these clusters to NMR signals reveals the presence of phosphonic-bridge conformers.
Datum: 01.02.2016

Synthesis of Bi–Fe–Sb–O Pyrochlore Nanoparticles with Visible-Light Photocatalytic Activity

A method has been developed for the preparation of Bi–Fe–Sb–O pyrochlore nanoparticles by microwave hydrothermal treatment. Experiments revealed that the preparation procedure for the precursors is an important factor that affects the phase composition of the product. The morphology of the pyrochlore particles was investigated by SEM, HRTEM, and selected-area electron diffraction (SAED) methods. The samples consist of numerous spherical agglomerates from 100 to 200 nm formed from 20 nm mutually oriented nanocrystallites. A mechanism for the formation of the particles is proposed, and the magnetic and photocatalytic properties of the Bi–Fe–Sb–O pyrochlore nanocrystallites are reported. Bi–Fe–Sb–O pyrochlore nanoparticles are synthesized by microwave hydrothermal treatment. The samples consist of 100–200 nm spherical agglomerates formed from 20 nm mutually oriented nanocrystallites. Some of the spheres are hollow. The photocatalytic activity of the pyrochlore nanoparticles is higher than that of TiO2.
Datum: 01.02.2016

The Reactivity of Diphenyllead(IV) Dichloride with Dissymmetric Thiosemicarbazone Ligands: Obtaining Monomers, Coordination Polymers, and an Organoplumboxane

The reaction of PbPh2Cl2 with two dissymmetric thiosemicarbazone ligands containing diacetyl 4-methyl-3-thiosemicarbazone and hydrazonepyridine or hydrazonequinoline arms led to four new mononuclear complexes, [PbPh2(L)] (1 and 3) and [PbPh2Cl(HL)] (2 and 4). Reactions with the hydrazonequinoline ligand strongly depend on the reaction conditions and several unexpected compounds were isolated. At room temperature, in addition to complex 4, the polymeric compound [PbPh2Cl2CH3OH]n (5) was isolated, whereas under heating at reflux a symmetrization took place and a polymer containing diacetyl bis(4-methyl-3-thiosemicarbazone), [PbPh2Cl2(H2ATSM)]n (6) was obtained. When PbPh2Cl2 was heated at reflux in wet dichloromethane with LiOH·H2O, the tetranuclear organoplumboxane [Pb4Ph8Cl4O2] (7) was isolated, which, to the best of our knowledge, is the first organoplumboxane to be crystallographically characterized. All the compounds were thoroughly characterized, including by 207Pb NMR and single-crystal XRD. In addition, the hydrazonequinoline ligand has demonstrated its potential application as a chromophoric probe in the visible region for organolead(IV) species. The reaction of PbPh2Cl2 with dissymmetric thiosemicarbazones strongly depends on the reaction conditions and leads to seven new compounds, including mononuclear complexes, coordination polymers, and an organoplumboxane, which, to the best of our knowledge, represents the first example of this kind of compound that has been crystallographically characterized.
Datum: 01.02.2016

Pseudomorphic Transformation of Layered Simple Hydroxides into Prussian Blue Analogue Nanoplatelets

The reactivity of potassium or sodium hexacyanoferrate(II) with transition-metal layered simple hydroxides (LSHs) has been investigated to evaluate the possibility of inserting Prussian Blue analogues (PBAs) into magnetic copper(II) LSHs. This report shows how such a reaction led, unexpectedly, to the direct formation of PBA nanoparticles, the layered hydroxide serving as a metal-ion reservoir. The lamellar structure of the starting LSH collapses and copper–iron PBA nanoparticles were obtained as well-defined cubic structures stacked in layers. In addition to structural and magnetic characterization, the reaction mechanism was investigated by 57Fe Mössbauer spectrometry and X-ray photoemission spectroscopy. The layered copper hydroxide acetate turns out to be a smart precursor of well-shaped PBA nanoparticle layers through pseudomorphic replication. Prussian Blue analogue nanoplatelets have been produced by pseudomorphic replication of layered Cu2(OH)3(OAc) in the presence of K4[Fe(CN)6]. A transformation mechanism is proposed. Our results demonstrate that lamellar simple hydroxides can be used as precursors of molecular-based networks and that the lamellar nature of the Cu reservoir favours the organization of crystallites into sheets.
Datum: 01.02.2016

Synthesis of Hexagonal-Phase Eu3+-Doped GdF3 Nanocrystals above Room Temperature by Controlling the Viscosity of the Solvents

The formation of orthorhombic-phase GdF3 nanocrystals (thermodynamically controlled product) requires higher activation energy than that necessary for the formation of hexagonal-phase GdF3 nanocrystals (kinetically controlled product). As a result, whenever a reaction is carried out at higher temperatures, formation of the orthorhombic-phase GdF3 is generally preferred. However, the thermodynamic product is always more stable than the kinetic one at lower temperatures. Here, we report a simple microwave-assisted method to synthesize stable, hexagonal-phase, polyvinylpyrrolidone (PVP) functionalized Eu3+-doped GdF3 nanocrystals at higher temperatures (up to 220 °C). This is achieved by tuning the viscosity of the solvents as well as using KF as fluoride source. Both the morphology and the size of the GdF3 nanocrystals can also be varied by tuning the reaction conditions. Functionalization of the nanocrystals with PVP makes them water-dispersible. The Eu3+-doped GdF3 nanocrystals show intense red emission and longer luminescence lifetimes. The high luminescence efficiency of the Eu3+-doped GdF3 nanocrystals together with their high dispersibility in water can make them suitable for use in bioimaging and MRI imaging applications. The synthesis of hexagonal-phase GdF3 nanocrystals at higher temperatures has been achieved by controlling the viscosity of the solvents used. Highly luminescent hexagonal-phase Eu3+-doped GdF3 nanocrystals were prepared above 200 °C.
Datum: 29.01.2016

An Easy Way to Construct Polyoxovanadate-Based Organic–Inorganic Hybrids by Stepwise Functionalization

Herein we report a step-by-step strategy for the organic modification of polyoxovanadates, which is based on a suitable polyoxovanadate platform, and a series of novel functionalized polyoxovanadates can be synthesized conveniently by sequential esterification and amidation reactions. A step-by-step functionalization methodology has been developed for the construction of complicated polyoxovanadate hybrids, and a series of novel functionalized polyoxovanadates have been synthesized by esterification and amidation reactions in a convenient and efficient way.
Datum: 29.01.2016

Phase Relations and Physical Properties of Layered Pb-Containing Nd2MoO6 Compounds

The phase relations along the Nd2MoO6–PbO join of the ternary Nd2O3–MoO3–PbO system have been studied by means of solid-state synthesis in air. The samples with high Pb content underwent a reversible first-order phase transition near 820 °C. XRD analysis revealed two tetragonal phases, the high-temperature centric phase (I41/acd) and the low-temperature acentric phase (I$\bar {4}$2m). In the region of the phase transition, the permittivity of the Pb-containing samples show a strong lambda-type anomaly and electrical conductivity increases sharply by one and half orders of magnitude. The conductivities of the Pb-containing samples reach 10–2 S/cm at 850 °C, which is two orders of magnitude greater than the conductivity of pure Nd2MoO6. The conductivity in such compounds may be due to oxygen ions. A permittivity anomaly, existence of a piezoelectric effect, and the symmetry change from acentric I$\bar {4}$2m to centric I41/acd may indicate an antiferroelectric nature of the phase transition. We report herein the synthesis, XRD characterization, and electrical properties of new lead-containing layered molybdates based on Nd2MoO6. In contrast to pure Nd2MoO6, these materials reveal first-order reversible phase transitions accompanied by dielectric anomalies, DSC events, and sharp jumps in conductivity. The conductivity reaches 10–2 S/cm at 850 °C and may be due to oxygen ions.
Datum: 29.01.2016

Bipyridinium-bis(carboxylate) Radical Based Materials: X-ray, EPR and Paramagnetic Solid-State NMR Investigations

The zwitterionic 1,1′-bis(4-carboxyphenyl)-4,4′-bipyridinium (bp4pc) has been synthesized and crystals of its hydrated form bp4pc·2H2O and of its protonated reduced form H-bp4pc have been obtained. Upon heating, bp4pc·2H2O undergoes partial dehydration, leading to bp4pc·H2O at 160 °C, together with a color change from yellow (room temperature) to green (140 °C) and finally to brown (160–180 °C). Analysis of bond lengths in the solid state reveals the expected short (d = 1.425 Å) and long (d = 1.485 Å) C–C central bond lengths in the all-radical salt H-bp4pc and bp4pc·2H2O, respectively, whereas the distance of 1.475 Å in bp4pc·H2O does not allow a conclusion to be drawn regarding the presence of radicals in this compound. EPR and solid-state paramagnetic NMR experiments of H-bp4pc and the hydrated zwitterion bp4pc·2H2O at different temperatures, however, show that the color change of the latter upon heating is due to the presence of bipyridinium radicals, the concentration of which, although low, increases with increasing temperature. The nature of the electron donor involved in this thermal-induced electron transfer is not fully understood. Most plausible is the possibility that it is the carboxylate group with an intramolecular electron-transfer process; on the other hand it, cannot be excluded that the electron stems from the water molecule, which decomposes into O2, H+, and e– giving H-bp4pc entities. Crystals of a bipyridinium-bis(carboxylate) ligand (bp4pc) have been synthesized in both the protonated reduced form and in the hydrated form. Upon heating, partial dehydration of the latter phase is accompanied by an electron-transfer process, resulting in the colored bp4pc·– radical, as revealed by solid-state NMR spectroscopy.
Datum: 29.01.2016

The Influence of Imidazolylidene Ligands with Bulky Resorcinarenyl Substituents on Catalysts for ­Suzuki–Miyaura Coupling

PEPPSI-type imidazolylidene palladium complexes having their carbenic ring N-substituted with an aryl ring and a cavity-shaped unit [25,26,27,28-tetrapropyloxycalix[4]aren-5-yl or 6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]aren-5-yl (TPR)] have been prepared and assessed in Suzuki–Miyaura cross-couplings. Remarkable efficiency in the coupling of aryl chlorides with sterically hindered arylboronic acids was observed for the carbene ligand having its N atoms (N1, N2) substituted by a mesityl and a TPR group, respectively. This good performance possibly arises from strong steric interactions between the pentyl-substituted cavitand unit and the catalytic centre, which favours reductive elimination. Two of the imidazolium salts used for complex synthesis were characterised by X-ray diffraction analysis. A palladium complex containing a bulky N-heterocyclic carbene ligand having one of its nitrogen atoms substituted by an extended cavitand, showed high efficiency in Suzuki–Miyaura cross-coupling of aryl chlorides with sterically hindered arylboronic acids.
Datum: 29.01.2016

A Series of Copper–Lanthanide Heterometallic Coordination Polymers Derived from Pyridine-2,3-dicarboxylic Acid and in situ Generated Succinic Acid

A series of copper–lanthanide heterometallic coordination polymers (CPs), [LnCu(2,3-pydc)2(suc)0.5(H2O)3]·H2O [Ln = La (1), Pr (2), Nd (3), Sm (4), Gd (5), and Eu (6), 2,3-H2pydc = pyridine-2,3-dicarboxylic acid, H2suc = succinic acid], [Ln2Cu3(2,3-pydc)6(H2O)10]·8H2O [Ln = Eu (7), Tb (8), Dy (9), and Er (10)], and [Ln2Cu(2,3-pydc)2(suc)(µ2-OH)2(H2O)2]·2H2O [Ln = Er (11), Yb (12), and Lu (13)], were synthesized by the hydrothermal reactions of LnCl3·nH2O, Cu(NO3)2·3H2O, pyridine-2,3-dicarboxylic acid (2,3-H2pydc), and N,N′-di(4H-1,2,4-triazole)butanamide (dtb). CPs 1–13 possess three types of three-dimensional (3D) frameworks. In 1–6, the dinuclear Cu2(2,3-pydc)4 and Ln2(COO)2 units link to each other to form two-dimensional (2D) layers, which are extended by the suc anions into a 3D framework. In 7–10, the lanthanide ions connect the trinuclear Cu3(2,3-pydc)6 units into a 3D framework. In 11–13, the mononuclear Cu(2,3-pydc)2 units bridge the one-dimensional (1D) lanthanide chains into 2D layers, which are linked by the suc anions into a 3D framework. CP 9 shows a field-induced slow magnetic relaxation behavior with a Ueff value of 83.7 K. A series of copper–lanthanide heterometallic coordination polymers (CPs) with three types of 3D frameworks and two structural critical points have been successfully synthesized and structurally characterized. The dysprosium-containing CP shows a field-induced slow magnetic relaxation behavior.
Datum: 29.01.2016

Hole-Size Relationships in the Assembly of a Furandicarboxylate-Based Metallolinker in Praseodymium Coordination Polymers Synthesized under Basic Conditions

Two new coordination polymers have been synthesized with 2,5-furandicarboxylic acid upon base modification. The resulting structures are dependent on the base added. When KOH was used as base, potassium was incorporated into the two-dimensional coordination polymer, acting as a metallolinker to give [Pr2K2(OH)2(C6H2O5)3(H2O)3]·H2O (1). Synthesis with other alkali hydroxides produced a three-dimensional metal-organic framework, [Pr8(OH)6(C6H2O5)9(H2O)15]·3H2O (2), and the alkali metal cations were not incorporated into the structure. Hole-size effects with bite-angle analyses indicate that metallolinker formation depends on the cation size. The resulting compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, and thermogravimetric analysis. Two new coordination polymers have been hydrothermally synthesized with 2,5-furandicarboxylic acid. The structures are dependent upon the base added. KI ions from KOH produce a metallolinker, whereas other bases did not result in metallolinker formation. Crystallographic analyses indicate that metallolinker formation is highly size-dependent.
Datum: 29.01.2016

Mononuclear Iron-(hydro/semi)­quinonate Complexes Featuring Neutral and Charged Scorpionates: Synthetic Models of Intermediates in the Hydroquinone Dioxygenase Mechanism

Neutral and anionic scorpionate ligands have been employed to generate active-site models of hydroquinone dioxygenases (HQDOs). While the nonheme Fe center in nearly all HQDOs is coordinated to one Asp (or Glu) and two His residues, 1,2-gentisate dioxygenase (GDO) is unique in featuring a three His triad instead. A synthetic GDO model was therefore prepared with the neutral tris(4,5-diphenyl-1-methylimidazol-2-yl)phosphine (Ph2TIP) ligand. The gentisate substrate was mimicked with the bidentate ligand 2-(1-methylbenzimidazol-2-yl)hydroquinonate (BIHQ). X-ray diffraction analysis of the resulting complex, [Fe(Ph2TIP)(BIHQ)]OTf (1a), revealed a distorted square-pyramidal geometry. Structural and electrochemical data collected for 1a were compared to those previously reported for [Fe(Ph2Tp)(BIHQ)] (1b), which features an anionic hydridotris(3,5-diphenylpyrazol-1-yl)borate (Ph2Tp) ligand. Oxidation of 1a and 1b provides the corresponding FeIII complexes (2a/2b) and the crystal structure of 2b is reported. Both complexes undergo reversible deprotonation to yield the brown chromophores, 3a and 3b. Detailed studies of 3a and 3b with spectroscopic (UV/Vis absorption, EPR, resonance Raman) and computational methods determined that each complex consists of a high-spin FeII center ferromagnetically coupled to a p-semiquinonate radical (BISQ). The (de)protonation-induced valence tautomerization described here resembles key steps in the putative HQDO mechanism. Both neutral and anionic scorpionates are used to prepare synthetic models of hydroquinone dioxygenases (HQDOs) – a class of mononuclear nonheme enzymes. The different ligands mimic variations in coordination geometry within the HQDO family. The ferric-hydroquinonate complexes undergo reversible deprotonation to yield ferrous-semiquinonate species.
Datum: 29.01.2016

Synthesis, Structural Characterization, and Catalytic Activity of Indenyl Tris(N-pyrrolyl)phosphine Complexes of Ruthenium

The synthesis, characterization, and catalytic activity of new ruthenium complexes of the tris(N-pyrrolyl)phosphine ligand [P(pyr)3] are described. The new ruthenium complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] (ind = indenyl, η5-C9H7–) were synthesized in 73 and 63 % isolated yields, respectively, by thermal ligand exchange of [RuCl(ind)(PPh3)2] with P(pyr)3. The electronic and steric properties of the new complexes were studied through analysis of the X-ray structures and cyclic voltammetry. The new complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] and the known complex [RuCl(ind){(PPh3)2}] differed only slightly in their steric properties, as seen from the comparable bond lengths and angles around the ruthenium centers. The oxidation potentials of [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] of +0.34 and +0.71 V versus Cp2Fe0/+ (Cp = cyclopentadienyl) are substantially higher than that of [RuCl(ind)(PPh3)2] (–0.023 V), in accordance with the enhanced π-acidity of the P(pyr)3 ligand. The new complexes are catalytically active in the etherification of propargylic alcohols and in the first ruthenium-catalyzed formation of known and new xanthenones from propargylic alcohols and diketones (18 to 72 h at 90 °C in ClCH2CH2Cl or toluene, 1–2 mol-% catalyst, 69–22 % isolated yields). The ruthenium tris(N-pyrrolyl)phosphine [P(pyr)3] complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] exhibit increased oxidation potentials owing to the π-acidic P(pyr)3 ligands. The complexes are catalytically active in the etherification of propargylic alcohols and in the formation of known and new xanthenones from propargylic alcohols and diketones.
Datum: 29.01.2016

Green Synthesis of Inorganic-Organic Hybrid Materials: State of the Art and Future Perspectives

The term “inorganic–organic hybrid materials” designates inorganic building blocks in the colloidal domain (1–1000 nm) embedded in an organic, typically polymeric, matrix. Owing to their outstanding properties, hybrid materials have the potential to improve human life significantly. In the last two decades, the importance of reorienting chemical syntheses in the direction of more sustainable, less harmful and energy-consuming procedures, referred to as green chemistry, has been much emphasized and worked on. This review deals with the application of green chemistry to the synthesis of inorganic–organic hybrid materials. The origin and preparation both of the inorganic components and of the organic polymer matrix are critically analyzed for various examples. The development of more sustainable syntheses for hybrid materials still poses an open challenge. Potential options to tackle this task are discussed. Inorganic–organic hybrids combine, for example, the mechanical and temperature stability of inorganic colloids with the light weight and processability of organic polymers. For their green synthesis, one has to combine benign approaches towards both constituents. This microreview summarizes green syntheses of both components and reviews the implementation of green chemistry for hybrid materials.
Datum: 29.01.2016

s-Block Metal Complexes with Bis- and Tris(pyrazolyl)methane and -methanide Ligands

Substituted bis- and tris(pyrazolyl)methanes and -methanides are isoelectronic with the corresponding pyrazolyl-substituted boranates, but the use of these Lewis bases in the coordination chemistry of the s-block metals has attracted attention only quite recently. Many lithium and magnesium complexes have been isolated and characterized, but for the heavier alkali and alkaline earth metals much less information is available. Beryllium complexes are unknown, due to the toxicity of this lightest alkaline earth metal. The bis- and tris(pyrazolyl)methanes and -methanides act as multidentate ligands to the metal ions and commonly bind through the pyrazolyl bases. The presence of the very rare κ2N,κC coordination mode of the tris(pyrazolyl)methanides destabilizes these ligands and leads to their degradation. This microreview presents syntheses, molecular structures, and characteristic spectroscopic properties of s-block metal complexes with bis- and tris(pyrazolyl)methane and -methanide ligands as well as with heteroscorpionate ligands. Furthermore, degradation of tris(pyrazolyl)methanides at heavy alkaline earth metals (especially of calcium) is discussed on the basis of experimental results and quantum chemical calculations. Deprotonation of substituted tris(pyrazolyl)methanes yields the corresponding tris(pyrazolyl)methanides, which show diverse coordination modes and susceptibility to degradation in the vicinity of heavy s-block metals, depending on the substitution pattern of the pyrazolyl rings.
Datum: 29.01.2016

What Can Electron Microscopy Tell Us Beyond Crystal Structures?

Transmission electron microscopy is a powerful tool to directly image crystal structures. Not only that, it is often used to reveal crystal size and morphology, crystal orientation, crystal defects, surface structures, superstructures, etc. However, due to the 2D nature of TEM images, it is easy to make mistakes when we try to recover a 3D structure from them. Scanning electron microscopy is able to provide information on the particle size, morphology and surface topography. However, obtaining information on crystallinity of particles using SEM is difficult. In this microreview article, some practical cases of transmission and scanning electron microscopy investigations of inorganic crystals are reviewed. Commonly occurring uncertainties, imperfection and misunderstandings are discussed. Some examples of conventional SEM and TEM studies of inorganic crystals are reviewed. Typical problems of misinterpretation of the images are discussed.
Datum: 27.01.2016

Ferrocenyl Dithiocarbamate Based d10 Transition-Metal Complexes as Potential Co-Sensitizers in Dye-Sensitized Solar Cells

Three new d10 transition-metal dithiocarbamates containing ferrocene, namely [M(FcCH2EtOHdtc)2] (M = Zn, Cd and Hg; dtc = dithiocarbamate) have been synthesized and characterized by elemental analyses, IR, 1H, and 13C NMR spectroscopy, and X-ray crystallography. The coordination geometries around the zinc and mercury ions in the complexes are distorted tetrahedral and distorted linear, respectively. The distorted linear geometry around the mercury complex can be attributed to the presence of the bulky methylferrocenyl groups. These complexes have been used in dye-sensitized solar cells (DSSCs) as co-sensitizers and co-adsorbents. The assembly fabricated by using the zinc complex and N719 (Zn/N719) showed the best performance with an overall photon-to-current conversion efficiency (PCE) of 7.10 ± 0.02 %, which is an improvement of 23 % in the cell performance compared with the DSSC fabricated by using N719 (PCE 5.76 ± 0.04 %) alone under identical conditions. Three new d10 transition-metal dithiocarbamates containing ferrocene have been synthesized and their application as co-sensitizers to the state-of-the-art dye N719 in dye-sensitized solar cells explored.
Datum: 27.01.2016

(Picrylamino)-1,2,4-triazole Derivatives – Thermally Stable Explosives

3-(Picrylamino)-1,2,4-triazole (PATO) and 3-amino-5-(picrylamino)-1,2,4-triazole (APATO) were synthesized and analyzed. During the syntheses of the compounds, two interesting side-products were isolated. The reactions of PATO and APATO with different nitrogen-rich bases, such as ammonia, hydrazine, triethylamine, and triaminoguanidine, resulted in the deprotonation of both triazole compounds and the formation of the corresponding salts (cation/anion ratio = 1:1). The compounds were obtained at ambient temperature in H2O or EtOH as qualitatively pure products with the characteristic properties of secondary explosives. The compounds were characterized by multinuclear NMR, IR, and Raman spectroscopy as well as mass spectrometry. The low-temperature structures of two compounds were determined by single-crystal X-ray diffraction. The thermal stabilities were measured by differential scanning calorimetry (DSC). The sensitivities were determined through the BAM drophammer and friction tests. The heats of formation were calculated by the atomization method from the CBS-4M enthalpies and the densities determined by X-ray diffraction or pycnometry. Several detonation parameters including the detonation pressure, detonation velocity, detonation energy, and detonation temperature were computed with the EXPLO5 code. New energetic and highly thermally stable salts of 3-(picrylamino)-1,2,4-triazole (PATO) and 3-amino-5-(picrylamino)-1,2,4-triazole (APATO) are synthesized. PATO shows high thermal stability with good energetic performance as a highly thermally stable explosive. The ammonium salt of PATO also shows promising energetic performance with a slightly lower thermal stability than that of neutral PATO.
Datum: 27.01.2016

Reactivity of Me-pma RhI and IrI Complexes upon Deprotonation and Their Application in Catalytic Carbene Carbonylation Reactions

Dehydrogenative oxidation of amines is a relevant process in metal-mediated catalysis, with the amines being either substrates or ligands. Transformation of amine- into imine-type ligands in the coordination sphere of a transition metal can be an important catalyst activation process. The behaviour of secondary pyridin-2-ylmethanamine (pma) ligands in the corresponding rhodium and iridium complexes upon NH deprotonation varies, depending on a number of factors. In this paper the behaviour of the Me-pma ligand [Me-pma = N-methyl-1-(pyridin-2-yl)methanamine] bound to [Rh(cod)]+ and [Ir(cod)]+ was studied. Whereas the iridium amido complex could be obtained upon NH deprotonation, the rhodium complex instantaneously disproportionated into a free pma ligand and an unusual dinuclear complex, adopting a structure with two RhI metal centres hosted by a dianionic (pma-2H)2– ligand, and with the ligand coordinating to Rh2 as an “aza-allyl” fragment. The study gives further proof for the effect of pyridine ligation on the previously observed charge-transfer from the ligand to the metal. Furthermore, the catalytic activity of both the Ir and the Rh species with Me-pma in carbene carbonylation reactions to generate ketenes was studied. The coordination chemistry of group 9 metals with a novel redox-noninnocent picolyl-amine-based ligand is elucidated through combined NMR spectroscopy and X-ray structure determination. The ability of these ligands to form both mono- and dinuclear metal complexes illustrates the versatile nature of such ligands. The mononuclear Rh complex is active in carbene carbonylation to generate ketenes.
Datum: 27.01.2016

Structural and Magnetic Properties of 57Fe-Doped TiO2 and 57Fe/Sn-Codoped TiO2 Prepared by a Soft-Chemical Process

A series of 57Fe-doped TiO2 and 57Fe/Sn-codoped TiO2 materials were prepared by a soft-chemical solution process with various 57Fe concentrations from 0.1 to 1.0 at.-% and a fixed Sn concentration of 2.0 at.-%. In this process, an aqueous H2O2 solution reacts with iron and titanium or iron, tin, and titanium precursor compounds to produce peroxopolymetallic acids. The structures and magnetic properties of the products were characterized by magnetic-moment measurements, X-ray diffraction, and Raman and Mössbauer spectroscopy. The results showed that all samples consisted of a rutile phase (and a trace amount of anatase in 57Fe-TiO2). All samples exhibited hysteresis loops in the M–H curves, which demonstrated the presence of room-temperature ferromagnetism. In addition, their magnetic properties decreased with increasing degree of 57Fe doping. Oxygen vacancies were considered to be responsible for the presence of ferromagnetism. Room-temperature ferromagnetism (RTFM) was found in 57Fe-TiO2 and 57Fe/Sn-TiO2 materials prepared by a soft-chemical solution method. Their magnetic properties were found to decrease with increasing degree of 57Fe doping. Fe3+–oxygen vacancy (VO)–Fe3+ centers are responsible for the observed RTFM.
Datum: 27.01.2016

A Periodic Walk through a Series of First-Row, Oxido-Bridged, Heterodimetallic Molecules: Synthesis and Structure

A series of heterodimetallic molecules, centered around an LTi=OM2+L′ (M = Mn, Fe, Co, Ni, Cu, Zn) core, are described. Each of these complexes are structurally similar, with L = tmtaa and L′ = Py5Me2. The Ti=OM linkage is slightly bent, varying from 157° (Mn) to 170° (Zn), with bond lengths typical of a dative bond between the Ti=O group and the M2+ center. The relative strength of the heterodimetallic linkage is correlated with the Lewis acidity of the M2+ precursor, with Mn2+ showing the strongest interaction and Ni2+ the weakest. By varying the metal identity the electrochemical properties of the molecules can be tuned, along with the M3+/2+ redox couple. This series of complexes provide a platform for studying structure/function relationships in heterodimetallic molecules linked through a single atom. For instance, spectroscopic features such as IR stretching frequencies can be roughly correlated with structural features such as bond lengths and angles. By using a Lewis-basic Ti=O group, a series of oxido-bridged heterodimetallic molecules comprised of earth-abundant first-row elements is described. By varying the metal identity of the Lewis-acidic center, molecular properties such as bridge stability and redox potentials can be tuned.
Datum: 26.01.2016

Molecular and Electronic Structure of the Cluster [Au8(PPh3)8](NO3)2

We present a detailed structural discussion of [Au8(PPh3)8](NO3)2, crystallized as a CH2Cl2 solvate. Its structure is compared with closely related triphenylphosphine-stabilized gold clusters. Characterization by optical extinction spectroscopy, luminescence spectroscopy, voltammetry and DFT calculations was performed to determine the electronic HOMO–LUMO gap. Comparison of its characteristic energies with those of structurally related clusters revealed that the evolution of the HOMO–LUMO gap does not follow a simple scaling law but depends on specific structural features. A detailed structural characterization together with an experimental (optical extinction spectroscopy, luminescence spectroscopy, voltammetry) and DFT-based analysis of the electronic structure of the triphenylphosphine-stabilized cluster [Au8(PPh3)8](NO3)2 gives an insight into structure–property relationships.
Datum: 25.01.2016

Lanthanide Complexation of 2,6-Bis(5,6-dipyridyl-1,2,4-triazinyl)pyr­idine – Solvent- and Lanthanide-Ion-Controlled Ligand Coordination Mode and Denticity

2,6-Bis(5,6-dipyridyl-1,2,4-triazinyl)pyridine (PyBTP) is an interesting ligand owing to the possible variation of its coordination sites and denticity in complexation. Therefore, solution and solid-phase lanthanide complexations were studied with PyBTP in two solvents, viz., acetonitrile and methanol, through various spectroscopic and single-crystal X-ray diffraction techniques. The results from all of these studies consistently showed the interesting observation of solvent-dependent changes to the ligand coordination mode and denticity, which are reported for the first time for trivalent lanthanide (Ln3+) complexes. The ligand coordination is affected by the size of the lanthanide ion. This observation can provide clues for the development of intra-lanthanide and lanthanide–actinide separation methods through the exploitation of the variable complexing behaviour of a particular ligand. Solvent- and metal-ion-dependent changes in the ligand coordination mode and denticity in the lanthanide complexes of 2,6-bis(5,6-dipyridyl-1,2,4-triazinyl)pyridine (PyBTP) are investigated through fluorescence spectroscopy, 1H NMR spectroscopy, UV/Vis spectrophotometry, attenuated total reflectance (ATR) FTIR spectroscopy, and single-crystal XRD.
Datum: 25.01.2016

Synthesis and Dynamic Behavior of Chiral NNO-Scorpionate Zinc Initiators for the Ring-Opening Polymerization of Cyclic Esters

The reaction of chiral alcohol–scorpionate compounds bpzbeH [bpzbeH = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butanol] or bpzteH [bpzteH = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-para-tolylethanol] with [ZnR2] (R = Me, Et, CH2SiMe3) in a 1:2 molar ratio afforded the dinuclear chiral zinc alkyls [Zn(R)(κ2-NNµ-O)Zn(R)2] (1–4) [κ2-NNµ-O = bpzbe, R = Me (1), Et (2), CH2SiMe3 (3); bpzte, R = Et (4)]. Subsequent alcoholysis or thioalcoholysis reaction with ArEH (1 equiv.; E = O, S; Ar = 2,6-C6H3Me2) yielded the chiral dinuclear mixed alkyl–alryl oxides/thioaryl oxides [(ZnR)2(κN:κN-µ-O)(µ-EAr)] (5–12) [κN:κN-µ-O = bpzbe, E = O, R = Me (5), Et (6), CH2SiMe3 (7); bpzte, E = O, R = Et (8); bpzbe, E = S, R = Me (9), Et (10), CH2SiMe3 (11); bpzte, E = S, R = Et (12)]. The alcoholysis reaction of the previously reported monoalkyls [Zn(Me)(κ3-NNO)] or [Zn(R)(κ-NNµ-O)]2 with ArOH (1 equiv., Ar = 2,6-C6H3Me2) afforded the chiral aryl oxides [Zn(OAr)(κ2-NNµ-O)]2 (13–14) [κ2-NNµ-O = bpzbe (13); bpzte (14)]. The X-ray crystal structures of 3, 5, 6, and 14 confirmed a dinuclear structure in all cases with the alkoxide of the heteroscorpionates in a µ-bridging mode between the ZnII centers. Variable-temperature NMR spectroscopic studies were carried out to study their dynamic behavior in solution. Complexes 1–9 and 12 can act as single-component initiators for the ROP of ϵ-CL and L-/rac-LA, and afforded materials with low molecular weights and narrow monomodal molecular weight distributions. MALDI-TOF mass spectra confirmed that for 5–8 the initiation occurred through nucleophilic attack by the alkoxide group, rather than the alkyl group, on the lactide monomer. Furthermore, inspection of the kinetic parameters showed propagations with a pseudo-first-order dependence on monomer and catalyst concentrations. Microstructural analysis of poly(rac-lactide) revealed that the mixed alkyl/aryl oxide-substituted initiators exert a moderate level of heteroselectivity (Ps = 0.66). A new series of chiral dinuclear trisalkyl- and alkyl–aryl oxide-containing zinc heteroscorpionates complexes, namely, [Zn(R)(κ2-NNµ-O)Zn(R)2] and [(ZnR)2(κN:κN-µ-O)(µ-OAr)], respectively, has been synthesized. Their dynamic behavior has been studied. Both families act as single-component living initiators for the ring-opening polymerization of ϵ-CL and L-/rac-LA.
Datum: 22.01.2016

Controlled Synthesis of Pnicogen–Chalcogen Polycations in Ionic Li­quids

Three new pnicogen–chalcogen polycations were synthesized under specific conditions in the Lewis-acidic ionic liquids (ILs) [EMIm]X·nAlX3 and [BMIm]X·nAlX3 (X = Cl, Br; [EMIm]: 1-ethyl-3-methylimidazolium, [BMIm]: 1-butyl-3-methylimidazolium) and crystallized as their tetrahalogenidoaluminate salts. Single-crystal X-ray diffraction revealed the new polycation [Bi6Te4Br2]4+ in triclinic [Bi6Te4Br2](AlBr4)4 as the reaction product of bismuth, tellurium, and bismuth tribromide. Substitution of the elements with Bi2Te3 yielded the heterocubane [Bi4Te4]4+ in tetragonal [Bi4Te4](AlBr4)4, which crystallizes isotypically to its known chlorine counterpart. The latter is also accessible from ILs. The interactions between cations and anions were evaluated by quantum-chemical calculations. Bi2S3, which is insoluble in most media, readily dissolves in the employed IL and forms the new augmented heterocubane [Bi3S4AlCl]3+, which crystallizes with the complex anion [S(AlCl3)3]2– as triclinic [Bi3S4AlCl][S(AlCl3)3]AlCl4. Quantum-chemical calculations support the assignment of elements in this compound. The monoclinic crystal structure of [Sb13Se16](AlCl4)6(Al2Cl7) contains a new member of the small family of pnicogen–chalcogen spiro-heterocubanes. Heteropolycations: Three new pnicogen–chalcogen polycations were synthesized in imidazolium-based Lewis-acidic ionic liquids (IL) at moderate temperatures. Bi2S3, usually soluble only under harsh conditions, readily dissolves and reacts in the employed IL to give a quaternary polycation. The choice of starting materials and the reaction temperature were identified as important control parameters.
Datum: 22.01.2016

Rare-Earth Metal Oxo/Hydroxo Clusters – Synthesis, Structures, and Applications

Multinuclear rare-earth metal coordination clusters bridged by oxo/hydroxo units have emerged from being lab curiosities to become a readily accessible class of compounds. New synthetic strategies for accessing these compounds on reasonable scales have been established. Clusters of different sizes have been investigated in terms of their magnetic and photophysical properties. Some preliminary biological applications have also been established. The synthesis and the structures of rare-earth metal oxo/hydroxo clusters are reviewed. The clusters are very robust, which makes them ideal materials for further chemical, physical, and biological studies.
Datum: 22.01.2016

Abnormal N-Heterocyclic-Carbene-Mediated Fixation of CO2 and N2O, and the Activation of Tetrahydro­furan and Tetrahydrothiophene under Ambient Conditions

A strong σ-donor abnormal N-heterocyclic carbene (aNHC), 1,3-bis(2,6-diisopropylphenyl)-2,4-diphenylimidazol-5-ylidene (L1), reacted with B(C6F5)3 in the presence of CO2 and N2O to form the adducts [aNHC·CO2·B(C6F5)3] (1) and [aNHC·N2O·B(C6F5)3] (2), respectively, in high yields at room temperature within a very short period of time. Furthermore, this aNHC/B(C6F5)3 reagent system was found to be very efficient for the ring-opening of tetrahydrofuran (thf) and tetrahydrothiophene (tht), affording 3 and 4, respectively, within 5–10 min at room temperature in good yields. Interestingly, this aNHC forms the air-stable Lewis acid/base adduct [aNHC·B(C6F5)3] (5) with B(C6F5)3 in the absence of any suitable substrate upon keeping this mixture in solution. DFT calculations showed that the Lewis acid/base adduct 5 is energetically less stable than compounds 1–4, and this may be the driving force for the formation of compounds 1–4 in the presence of small molecules such as CO2, N2O, thf and tht. All the new compounds were characterized spectroscopically (1H, 13C, 19F and 11B NMR, IR spectroscopy) in solution and the solid-state structures were unambiguously established by single-crystal X-ray diffraction analysis. The abnormal N-heterocyclic carbene, 1,3-bis(2,6-diisopropylphenyl)-2,4-diphenylimidazole-5-ylidene, reacts with B(C6F5)3 in the presence of CO2 or N2O to form [aNHC·CO2·B(C6F5)3] or [aNHC·N2O·B(C6F5)3], respectively, in high yields at room temperature within a very short period of time.
Datum: 22.01.2016

Synthesis of a Luminescent Azaphosphole

A carbazole-based azaphosphole (compound 3) has been prepared by acid-catalyzed dehydrocyclization of 1-phosphino-9H-carbazole (2) with benzoyl chloride. Unlike other benzazaphospholes having σ2,λ3-multiply bonded phosphorus atoms, compound 3 displays significant fluorescence in solution, as does primary phosphine 2. Compound 3, as well as the materials on route to its synthesis, were characterized by multinuclear NMR, UV/Vis, and fluorescence spectroscopy. The optical data of 2 and 3 are consistent with results of DFT and TDDFT [6-311G+(d,p) CAMB3LYP] calculations. The computed structure of compound 3′ (R = Ph) is also consistent with the experimental X-ray structural determination, which reveals a planar heterocyclic system and slight rotation of the p-tolyl group out of plane with respect to the heterocyclic core. A carbazole-based azaphosphole (compound 3) has been prepared by acid-catalyzed dehydrocyclization of 1-phosphino-9H-carbazole (2) with benzoyl chloride. Compounds 2 and 3 display significant fluorescence in solution.
Datum: 21.01.2016

Reactivity of Hydride Half-Sandwich Ruthenium(II) Complexes Bearing the Scorpionate Ligands Hydridotris(pyrazol-1-yl)borate and Tris(pyrazol-1-yl)methanesulfonate

The hydride complexes [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) and [RuH{κ3(N,N,N)-Tpms}(pta)2] (3) [Tp = hydridotris(pyrazol-1-yl)borate, Tpms = tris(pyrazol-1-yl)methanesulfonate, pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane] reacted with alkynes to form the corresponding neutral alkenyl complexes through insertion reactions. The addition of HBF4 to the hydride complex [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] (1) led to a coordinatively unsaturated complex through the loss of hydrogen. The free coordination site can be occupied by different groups, such as BF4 or NCMe. The hydride complexes [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] and [RuH{κ3(N,N,N)-Tpms}(pta)2] react with alkynes to form neutral alkenyl complexes. The complex [RuH{κ3(N,N,N)-Tp}(PPh3)(pta)] also reacts with HBF4 to give [Ru(FBF3){κ3(N,N,N)-Tp}(PPh3)(pta)]. A new ruthenium complex bearing a κ2(N,N)-Tpms ligand has been isolated and fully characterized.
Datum: 21.01.2016

Facile Preparation of AgI/Bi2MoO6 Heterostructured Photocatalysts with Enhanced Photocatalytic Activity

Bi2MoO6 microspheres were modified by loading AgI nanoparticles on their surfaces by a facile deposition/precipitation approach. The as-prepared AgI/Bi2MoO6 heterostructured photocatalysts exhibit much higher photocatalytic activities for the degradation of rhodamine B (RhB) and bisphenol A (BPA) than P25, AgI, Bi2MoO6, and a mechanical mixture of AgI and Bi2MoO6. The composite with 20 wt.-% AgI shows the highest degradation efficiency. The enhanced photocatalytic properties of the AgI/Bi2MoO6 heterostructures are attributed to their larger surface areas, extended absorption in the visible-light range, and efficient separation of photoinduced carriers at the interfaces of the AgI and Bi2MoO6 nanocrystals. The AgI/Bi2MoO6 photocatalyst is stable during the catalytic reaction and can be used repeatedly. Moreover, O2·– and h+ were verified as the main active species in the decomposition of organic pollutants. A possible photocatalytic mechanism is also proposed. Bi2MoO6 microspheres were modified by loading AgI nanoparticles on their surfaces by a facile deposition/precipitation approach. The AgI/Bi2MoO6 heterostructured photocatalysts exhibit high photocatalytic activities and high stabilities towards the degradation of rhodamine B and bisphenol A.
Datum: 20.01.2016

Expanding the Family of Uranium(III) Alkyls: Synthesis and Characterization of Mixed-Ligand Derivatives

The generation of uranium(III) alkyls supported by hydrotris(pyrazolyl)borate (Tp) and pentamethylcyclopentadienyl (Cp*) ligands is reported. Mixed ancillary ligand frameworks were synthesized by treating TpUI2(THF)3 (1) and Cp*UI2(THF)3 with potassium hydrotris(pyrazolyl)borate salts. Addition of one equivalent of potassium hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) generated TpTp*UI (2), while treatment of Cp*UI2(THF)3 with either KTp or KTp* resulted in the respective formation of Cp*TpUI(THF) (3) or Cp*Tp*UI(THF) (4). Alkylation of 2 with KCH2Ph or NaCH2SiMe3 furnished TpTp*UCH2Ph (2-CH2Ph) or TpTp*UCH2SiMe3 (2-CH2SiMe3). Similarly, treatment of 3 with NaCH2SiMe3 formed Cp*TpUCH2SiMe3 (3-CH2SiMe3), whereas treatment of 4 with KCH2Ph generated Cp*Tp*UCH2Ph (4-CH2Ph). All compounds were characterized by multinuclear NMR, IR, and electronic absorption spectroscopy. Compounds 2-CH2Ph, 3, and 3-CH2SiMe3 were structurally characterized using X-ray crystallography as well. The generation of uranium(III) monoiodide and alkyls supported by both hydrotris(pyrazolyl)borate (Tp) and pentamethylcyclopentadienyl (Cp*) ligands is reported.
Datum: 20.01.2016

The Stereoselective Self-Assembly of Chiral Metallo-Organic Cryptophanes

Cryptophanes are macropolycyclic cyclophanes constructed from two triply bridged concave cyclotriveratrylene analogues that encapsulate a large range of molecular and monoatomic substrates. Self-assembled metallo-organic cryptophanes based on M2+–carbonitrile (M = Pd or Pt) interactions have been obtained through the reactions of chiral nitrile-substituted cyclotribenzylenes (CTBs) 1 and 2 with [M(dppp)][OTf]2 (dppp = 1,3-bisdiphenylphosphinopropane, OTf = triflate) in 2:3 ratios in chlorinated solvents. The cryptophanes [Pd3(dppp)3(1)2]6+ and [Pd3(dppp)3(2)2]6+ were obtained exclusively in the chiral anti form in solution at room temperature whatever solvent was used; however the meso,syn form was identified as the major isomer of [Pd3(dppp)3(1)2]6+ at low temperature in CD2Cl2, and – in the case of [Pt3(dppp)3(1)2]6+ – it formed in a minor amount at room temperature. [Pd3(dppp)3(1)2][OTf]6 and [Pt3(dppp)3(1)2][OTf]6 crystallized in the anti forms with an encapsulated chloroform molecule, and gas-phase DFT calculations with the dispersion-corrected B97-D3 functional show that it is stabilized by 34.6 kJ mol–1. Interestingly, the heteroleptic cryptophane [Pd3(dppp)3(1)(2)]6+ was not detected in mixtures of [Pd(dppp)]2+ and CTBs 1 and 2 in a 3:1:1 ratio or through the equilibration of a 1:1 mixture of the preformed homoleptic cryptophanes; this points to favored self-sorting processes. The reactions of racemic cyclotricyanotribenzylene (1) and cyclotricyanotrianisylene (2) with [M(dppp)][OTf]2 (M = Pd or Pt; dppp = 1,3-bisdiphenylphosphinopropane, OTf = triflate) in 2:3 ratios afford the anti forms of the cryptophanes [M3(1)2(dppp)3][OTf]6 and [M3(2)2(dppp)3][OTf]6 stereoselectively. The assemblies of 1 encapsulate CHCl3 molecules in the solid state.
Datum: 19.01.2016

Allylic C–H Activation of Olefins by a TpMe2IrIII Compound

The IrIII compound [TpMe2Ir(C6H5)2(N2)] (1) [TpMe2 = hydridotris(3,5-dimethylpyrazolyl)borate] reacts with 1-hexene, propene, α-methylstyrene, and 2,3-dimethylbutadiene to yield organometallic products that derive from allylic C–H activations (complexes 3 from 1-hexene, 2 from propene, 5 from α-methylstyrene, and 7, 8, and 9 from 2,3-dimethylbutadiene), in all cases along with organic products formed in catalytic (Ir-induced) dehydrogenative coupling of benzene (the solvent of the reaction) and the corresponding olefin, with the latter also acting as the hydrogen scavenger in each case. Differently, complex 1 reacts with (E)-β-methylstyrene and cyclohexadiene to yield complex 2 and the known (η4-cyclohexadiene)IrI derivative 6, respectively. Finally, compound 1 reacts under mild conditions with cyclopentadiene and methylcyclopentadiene with the generation of phenyl derivatives 11 and 12 in which the corresponding cyclopentadienyl ligand adopts the η5 coordination and forces the TpMe2 ligand to coordinate in the κ2 mode. The IrIII complex [TpMe2Ir(C6H5)2(N2)] [TpMe2 = hydridotris(3,5-dimethylpyrazolyl)borate] reacts with different olefins to yield organometallic compounds that derive from allylic C–H activations in processes that also generate organic coupling products that involve the vinylic positions of the olefin.
Datum: 19.01.2016

Multiple Modes of Motion: Realizing the Dynamics of CO Adsorbed in M-MOF-74 (M = Mg, Zn) by Using Solid-State NMR Spectroscopy

Metal–organic frameworks (MOFs) often exhibit high porosities and surface areas, making them ideal media for gas storage and carbon capture. MOF-74 is an intriguing porous MOF featuring one-dimensional honeycomb-shaped channels and open metal sites, and is able to adsorb poisonous CO. Variable-temperature (VT) 13C solid-state NMR (SSNMR) experiments focusing on 13CO adsorbed within M-MOF-74 (M = Mg, Zn) are a sensitive probe of guest motion, revealing valuable details regarding the dynamics of adsorbed CO within the MOF channels. 13C SSNMR experiments recorded at temperatures ranging from 153 to 373 K, along with accompanying simulations, unambiguously indicate that two types of dynamic CO motion are present in MOF-74: a localized wobbling of CO on the open metal site, and a non-localized hopping of CO molecules between adjacent open metal sites. The fine details of these motions, including the motional angles and rates, are revealed and discussed. The CO dynamics in MOF-74 are then compared and contrasted with those of CO2, illustrating the similarities and differences in motion between the two types of guest molecules across the experimental temperature range. CO dynamics in M-MOF-74 (M = Mg, Zn) are comprehensively described. There are two types of CO motion: a localized sixfold wobbling and a non-localized sixfold hopping. The wobbling angles are inversely proportional to CO heats of adsorption. CO and CO2 motional data in MOF-74 confirm that the wobbling angle of these guests is very sensitive to several factors.
Datum: 19.01.2016

Amino Acid Interleaved Layered Double Hydroxides as Promising Hybrid Materials for AA2024 Corrosion Inhibition

Various α-amino acid (αAA) molecules were screened for their ability to retard the corrosion of AA2024 aluminum alloy substrate. The αAAs screened were L-arginine (L-Arg), L-asparagine (L-Asn), L-cysteine (L-Cys), L-cystine, L-histidine (L-His), L-methionine (L-Met), L-phenylalanine (L-Phe), L-serine (L-ser), L-tryptophan (L-Trp), and L-tyrosine (L-Tyr). From their performances compared with that of the reference additives chromate and 2-mercaptobenzothiazolate (MBT), L-Cys and L-Phe were selected, and their layered double hydroxide (LDH) interleaved derivatives were further scrutinized. Different LDH phases, namely, LiAl2, Mg2Al, MgZnAl, and Zn2Al, were tested as hosts for the inhibitor αAA substances, and the materials were characterized by XRD, FTIR spectroscopy, and SEM. The efficiencies and durable performances of the hybrid materials as an anticorrosion agents for aluminum alloy 2024 (AA2024) were demonstrated through direct current (DC) polarization measurements, and the evolution of the polarization resistance was recorded. The mechanism of inhibition focused on the most promising hybrid material LDH/L-Cys and was tentatively explained as anion exchange and dissolution of the inorganic framework at the cathodic and anodic corrosion zones, respectively, with the particular occurrence of Cu-rich intermetallic zones. The obtained results evidence that the LDH/L-CYS assembly embedded in the polymer coating retards the corrosion process of the AA2024 substrate after a prolonged immersion time. An assembly composed of L-cysteine (L-Cys) intercalated into a layered double hydroxide (LDH) is used as an ion-exchange inorganic functionalized filler dispersed in an epoxy-based primer layer. Upon corrosion, L-Cys molecules are released from the LDH container either by anion exchange or platelet dissolution and retard the corrosion of aluminum alloy AA2024 efficiently.
Datum: 19.01.2016

Ca9Sc(PO4)7:Ce3+,Mn2+ – A Red-Emitting Phosphor Based on Energy Transfer

A series of novel color-tunable phosphors, Ca9Sc(PO4)7:xCe3+,yMn2+ (CSP:xCe3+,yMn2+), have been synthesized by traditional high-temperature solid-state reactions. The optical properties of CSP:xCe3+ and CSP:0.02Ce3+,yMn2+ were systematically investigated with various spectral technologies. A phosphor with a broad, deep-red emission, CSP:0.02Ce3+,0.1Mn2+, was prepared by an energy transfer process with the CIE chromaticity coordinates (0.669, 0.307). CSP:Ce3+,Mn2+ phosphors excited at 254 nm display two broad emission bands: one centered at around 360 nm is assigned to the 5d1–4f1 electronic transition of Ce3+ ions, and the other at about 650 nm is attributed to the 4T1 (4G) 6A1 (6S) transition of Mn2+ ions. The energy transfer mechanism from Ce3+ to Mn2+ in the CSP:Ce3+,Mn2+ samples was discovered to be the dipole–dipole interaction, which was confirmed by the estimated critical distance between Ce3+ and Mn2+ (13.0 Å) by the spectral overlap method. Furthermore, the higher thermal stability of CSP:Ce3+,Mn2+ makes it feasible for a potential application in white-light-emitting diodes (WLEDs). A phosphor with a broad, deep-red emission, Ca9Sc(PO4)7:0.02Ce3+,0.1Mn2+ (CSP:0.02Ce3+,0.1Mn2+), was prepared by energy transfer from Ce3+ to Mn2+ through a dipole–dipole interaction. CSP:Ce3+,Mn2+ phosphors excited at 254 nm emit light in two bands: one at around 360 nm, assigned to the 5d1–4f1 transition of Ce3+, and the other at about 650 nm, derived from the 4T1 (4G) 6A1 (6S) transition of Mn2+.
Datum: 19.01.2016

Selenium-Substituted Phosphaalk­enes Obtained through 1,2-Elimination of Chlorosilanes from Selenen­ylchlorophosphines

Stable selenenyl-chlorophosphines, bearing a silylalkyl group, were synthesized. Subsequent treatment with Lewis acids such as AlCl3 afforded the corresponding phosphaalkenes. A reaction mechanism that proceeds through an intramolecular 1,2-elimination of chlorosilane was proposed. Stable selenenyl-chlorophosphines, bearing a trisilylalkyl group, were synthesized, and their treatment with Lewis acids such as AlCl3 afforded the corresponding phosphaalkenes. The experimental results and theoretical calculations suggested that the reaction proceeds through the intramolecular 1,2-elimination of chlorosilanes
Datum: 21.12.2015

Synthesis of 2-Phosphaindolizine and [1,3]Azaphospholo[1,5-a]quin­oline

The reaction of (chloromethyl)dichlorophosphine (1) with 2-[(trimethylsilyl)methyl]pyridine (6) and 2-[(trimethylsilyl)methyl]quinoline (12) in THF affords unsubstituted parent 2-phosphaindolizine (5) and [1,3]azaphospholo[1,5-a]quinoline (7). Multinuclear low-temperature NMR spectroscopy was used to investigate the reaction mechanism; a cascade of substitution and cyclization steps involving transient picolylphosphines and phosphorus heterocycles was identified. The molecular and crystal structures of two heterocyclic intermediates and of 7 were determined by single-crystal X-ray diffraction. Moreover, all intermediates and products were characterized by multinuclear 1H, 13C and 31P NMR spectroscopy. A synthetic procedure for preparing 1- and 3-unsubstituted 2-phosphaindolizines has been developed. This new method starts from ClCH2Cl2, PicolylTMS or QuinaldinylTMS and a base to form the desired azaphosphole as the only phosphorus-containing species.
Datum: 15.12.2015

Recent Developments in the Chemistry of 3H-1,2,3,4-Triazaphos­phole Derivatives

Datum: 07.12.2015

Sterically Protected Diphosphenes

Diphosphenes with various kinds of sterically protecting groups are described and discussed with regard to 31P NMR spectroscopic data, X-ray results, preparative methods, and some reactions including end-on coordination complex formations. New results of theoretical calculations on the particular diphosphene (E)-Mes*P=PMes* are also described. (E)-Bis(2,4,6-tri-tert-butylphenyl)diphosphene was prepared in 1981 for the first time, as a stable compound containing an isolated low-coordinate P=P bond. Since then many sterically protected diphosphenes with various substituents have been prepared, showing remarkable physicochemical features and interesting chemical reactivity.
Datum: 02.12.2015

Reactions of Li/Cl Phosphinidenoid Complexes with 1,3,4,5-Tetramethylimidazol-2-ylidene: A New Route to N-Heterocyclic Carbene Adducts of Terminal Phosphin­idene Complexes and an Unprecedented Transformation of an Oxaphosphirane Complex

The reaction of Li/Cl phosphinidenoid tungsten(0) complex 2 [R = CH(SiMe3)2] with 1,3,4,5-tetramethylimidazol-2-ylidene (3) yielded the zwitterionic phosphaalkene complex 4. A comparative study on chloro- (5) or dichloro(organo)phosphane complexes 1 [R = CH(SiMe3)2] and NHC 3 revealed the formation of 4 at ambient temperature. First evidence for the formation of phosphinidenoid complex 7, having a C-Cl imidazolium cation, and its reaction with benzaldehyde to give oxaphosphirane complex 9 are presented. Furthermore, the first example of a formal exchange at the phosphorus center of an oxaphosphirane complex to give zwitterion 4 is demonstrated. Reaction of P-Cl phosphinidenoid complexes and an oxaphosphirane complex with an N-heterocyclic carbene (NHC) to give a new zwitterionic phosphaalkene complex is described; the last-named can also be regarded as an NHC adduct of a terminal phosphinidene complex.
Datum: 25.11.2015

Synthesis and Structure of Lewis-Base-Free Phosphinoalumane Derivatives

Lewis-base-free diphosphinoalumane and 1-hydro-2-chlorophosphinoalumane derivatives bearing a bulky aryl substituent were synthesized by the reaction of the corresponding lithium phosphide and dichloroalumane. Structures of these phosphinoalumane derivatives were determined by spectroscopic and X-ray crystallographic analyses. Because of the efficient steric protection by the bulky aryl substituent, the aluminum centers in these phosphinoalumane derivatives have tricoordinate geometry. Reactions of the phosphinoalumane derivatives with organolithium reagents and bases were investigated. Lewis-base-free diphosphinoalumane and 1-hydro-2-chlorophosphinioalumane derivatives bearing a bulky aryl substituent were synthesized from the corresponding lithium phosphide and dichloroalumane. Their structures were determined spectroscopically and by X-ray crystallography. Because of the efficient steric protection by the bulky aryl substituent, their aluminum centers are tricoordinate.
Datum: 13.11.2015

Optically Active P5-Deltacyclenes: A Unique Cage-Inversion Reaction and Some Transition-Metal Complexes of the Rearranged Cage

Cage-chiral P5-deltacyclene 1 is available as a pair of highly enriched P–C cage enantiomers 1′ and 1″, which exist as pairs of epimers a and b. Deprotonation of cage atom P1 initiates a rearrangement reaction, in which P1 and the neighboring carbon atom C4, together with its substituent, change places to form optically active iso-P5-deltacyclene enantiomers 6″ and 6′, again as pairs of epimers. The CD spectra of related pairs of optically active cages 1 and 6 consist of almost mirror-symmetric curves, an indicator of mirror-symmetric cage structures. This surprising result was verified by an absolute structure determination of the W(CO)5 complex 9a″. With the exception of the two cage nuclei that had changed places in relation to starting material 1′, all other cage nuclei of rearrangement product 6a″ occupy mirror-symmetric positions. To the best of our knowledge, this represents the first cage-inversion reaction of an optically active compound. P1 is the only active donor center of 6 involved in the bonding of M(CO)5 fragments (M = Cr, Mo, W). The chiroptical properties of Cr(CO)5 complex 7a′ and W(CO)5 complex 9a″ are almost mirror-symmetric and resemble those of the free cages 6′ and 6″, respectively. The coordinated transition-metal complex fragments do not contribute significantly to the Cotton effects of the P–C cage. A DFT analysis of the deprotonated cage anions [1 – H]– and [6 – H]– predicts a driving force of –20.3 kcal mol–1 for the rearrangement reaction. Cage-chiral P–C cage compounds are a new class of chiral ligands. A stereoselective rearrangement performed with highly enriched P5-deltacyclene enantiomers is accompanied by a unique cage inversion, which results in almost mirror-symmetric CD curves of related pairs of P5-deltacyclene/iso-P5-deltacyclene enantiomers. The absolute structure of a W(CO)5 complex enantiomer confirms the observation.
Datum: 13.11.2015

Electron-Rich Aromatic 1,3-Heterophospholes – Recent Syntheses and Impact of High Electron Density at σ2P on the Reactivity

This account reviews recent syntheses, properties, and the reactivity of electron-rich aromatic 1,3-heterophospholes, with the focus on benzazaphospholes, but also with inclusion of 1,2,4-diazaphospholes containing the N–C=P–C motif and related O- and S-containing heterocycles. Effects of the high electron density at phosphorus, a consequence of the position of the lone-pair donating nitrogen atom in conjugation with dicoordinated (σ2) phosphorus and of the absence of P–N bonds, are illuminated by comparison of selected properties and reactions with those of less electron-rich heterophospholes and phosphinines. Particular features of the electron-rich heterocycles are CH-lithiations of the P=CH fragment by tBuLi without addition at the P=C double bond in polar media, occurrence of inverse addition besides normal addition in less polar solutions, P-alkylation and catalytic P-arylation, and – last but not least – the avoidance of σ-coordination of non-zerovalent d10 transition metals within the ring plane in favor of μ2-P and/or tilted η1-P coordination. The synthesis, properties, and reactivity of π-excess aromatic σ2P-heterocycles containing the X–C=P–C motif are reviewed. High electron density at σ2P gives these compounds a special position among the σ2P-heterocycles, allowing CH- and NH-lithiation, ambident reactivity of the anions, P-alkylation, catalytic P-arylation, and exclusively μ2- and/or tilted η1-P-coordination in d10 metal complexes.
Datum: 10.11.2015

Synthesis and Photoluminescence Properties of CuI Complexes with Chelating Phosphinito Phosphinine Ligands

The reaction between the sodium salt of 2-oxyphosphinine and diphenylchlorophosphine leads to 2-diphenylphosphinite phosphinine as a new chelating ligand. Copper(I) complexes are easily and quantitatively obtained when this compound is reacted with CuIX (X = Cl, Br, I). The optical properties of these complexes were investigated; all of them show phosphorescence in the solid state at room temperature and emit orange-red light in the range 658 to 702 nm with average lifetimes from 19.98 to 25.01 μs. The emission wavelength is tuned by the nature of the halide ligand: Cl–, which leads to a larger ligand-field splitting, gives the longest emission wavelength, whereas I–, which generates a smaller ligand-field splitting, leads to the shortest emission wavelength. Dinuclear copper(I) halide complexes with a new diphenylphosphinite phosphinine as chelating ligand were prepared. They show tunable phosphorescence in the range 650–700 nm in the solid state at room temperature.
Datum: 09.11.2015

Ambient-Temperature Synthesis of 2-Phosphathioethynolate, PCS–, and the Ligand Properties of ECX– (E = N, P; X = O, S)

A synthesis of the 2-phosphathioethynolate anion, PCS–, under ambient conditions is reported. The coordination chemistry of PCO–, PCS– and their nitrogen-containing congeners is also explored. Photolysis of a solution of W(CO)6 in the presence of PCO– [or a simple ligand displacement reaction using W(CO)5(MeCN)] affords [W(CO)5(PCO)]– (1). The cyanate and thiocyanate analogues, [W(CO)5(NCO)]– (2) and [W(CO)5(NCS)]– (3), are also synthesised using a similar methodology, allowing for an in-depth study of the bonding properties of this family of related ligands. Our studies reveal that, in the coordination sphere of tungsten(0), the PCO– anion preferentially binds through the phosphorus atom in a strongly bent fashion, while NCO– and NCS– coordinate linearly through the nitrogen atom. Reactions between PCS– and W(CO)5(MeCN) similarly afford [W(CO)5(PCS)]–; however, due to the ambidentate nature of the anion, a mixture of both the phosphorus- and sulfur-bonded complexes (4a and 4b, respectively) is obtained. It was possible to establish that, as with PCO–, the PCS– ion also coordinates to the metal centre in a bent fashion. We report a synthesis of the 2-phosphathioethynolate anion, PCS–, under ambient conditions. The coordination chemistry of PCO–, PCS– and their nitrogen-containing congeners is also explored.
Datum: 04.11.2015

A Rational Synthetic Approach to 2,5-Diphenyl-β-silyl Phospholes

Systematic access to β-silyl-substituted phospholes is reported. The synthesis proceeds through the addition of lithium phosphanide to a diyne and silylation of the intermediate β-lithio phosphole. By following this approach, mono and disilylation has been accomplished and the reactivity of the β-silyl phospholes towards oxidation with chalcogens and conversion into phospholides has been explored. The silyl units have a significant impact on the fluorescence properties of the phosphole system, leading to increased Stokes shifts and blueshifted absorption with redshifted emission. The key compounds have been characterized by multinuclear NMR spectroscopy, mass spectrometry, and, in part, by single-crystal X-ray diffraction analysis. Tuning the fluorescence of phospholes is possible by placing silyl units in the β-position. A general access to these compounds has been opened by modification of a classical procedure.
Datum: 04.11.2015

Synthesis and Luminescence Properties of Cycloplatinated Complexes with a Chelating N∧C Pyridine-Derived N-Heterocyclic Carbene – Influence of 2,4,6-Triphenyl­phosphinine versus Triphenylphosphine

Two cycloplatinated complexes of the form [Pt(NC)CH3(P)]+ incorporating a rare, bidentate NC-chelating pyridylpyridylidene ligand are reported. The phosphorus-based ligand P is either 2,4,6-triphenylphosphinine or triphenylphosphine. These mononuclear complexes have been fully characterised in solution and by single-crystal X-ray diffraction analysis. UV/Vis absorption and photoluminescence spectroscopy studies reveal strong phosphorescence from the phosphinine compound at 77 K but no emission from its triphenylphosphine analogue. This contrasting behaviour can be traced to the π-acceptor ability of the phosphabenzene ring, as corroborated by electrochemical and time-dependent DFT (TD-DFT) calculations. Two cycloplatinated complexes with a rare bidentate pyridylpyridylidene NC ligand and triphenylphosphine or 2,4,6-triphenylphosphinine coligands are synthesised and characterised. The phosphinine compound is strongly phosphorescent at 77 K, in contrast to the triphenylphosphine counterpart; this behaviour is probably the result of the exceptional π-acceptor ability of the phosphabenzene ring.
Datum: 30.10.2015

Reaction of P4 with in situ Formed cyclo-Triphosphatriazenium Cation [(DmpNP)3Cl2]+ (Dmp = 2,6-Dimethylphenyl)

The controlled activation of white phosphorus, P4, provides a key entry point into many aspects of polyphosphorus chemistry. Herein, the reaction of cyclo-diphosphadiazane derivative (DmpNPCl)2 (3a; Dmp = 2,6-dimethylphenyl) and P4 in the presence of GaCl3 as Lewis acid for the targeted synthesis of mono- and dicationic phosphorus-rich cage compounds [(DmpNP)2(P4)Cl][GaCl4] (8a[GaCl4]) and [(DmpNP)2(P4)2][Ga2Cl7]2 (9a[Ga2Cl7]2) is reported. Depending on the reaction conditions, formation of these types of cages, which are similar to those of the known cations [(DippNP)2(P4)Cl]+ (8b+) and [(DippNP)2(P4)2]2+ (9b2+; Dipp = 2,6-diisopropylphenyl) is observed. However, due to the reduced steric requirements of the Dmp compared to the Dipp group, an interconversion process of the P2N2 framework of cyclo-dichlorodiphosphadiazane 3a with the cyclo-trichlorotriphosphatriazane 5a is observed, which leads also to the formation of mono- and dicationic derivatives [(DmpNP)3(P4)Cl2]+ (10a+) and [(DmpNP)3(P4)2Cl]2+ (11a2+) via cyclo-triphosphatriazenium cation [(DmpNP)3Cl2]+ (4a+). The controlled reaction of P4 with in situ formed cyclo-triphosphatriazenium cation [(DmpNP)3Cl2]+ (Dmp = 2,6-dimethylphenyl) leads to the formation of mono- and dicationic derivatives [(DmpNP)3(P4)Cl2]+ and [(DmpNP)3(P4)2Cl]2+. The insertion reaction proceeds via a dicoordinate, cyclic phosphenium cation.
Datum: 28.10.2015

Phosphorus-containing multiple-bond systems have received great interest in various applications but often require elaborate syntheses and special precursors. In this paper, we describe simple methods for the synthesis of imidazoyl phosphinidenes and bis(imidazolyl)–P(I) halides from elemental phosphorus or the heptaphosphides Na3P7 and (Me3Si)3P7. The reactions of imidazolium salts with KOtBu and P4 afford mixtures of imidazoyl phosphinidenes and Pn compounds and, for N-methylated imidazolium salts, also bis(imidazolyl)–P(I) halides. NMR spectroscopy studies revealed the formation of a bis(imidazoyl)-substituted tetraphosphatriene and the bicyclic anion HP4– as transient intermediates and indicated the participation of tBuOH in the formation of imidazoyl phosphinidenes. Na3P7 and (Me3Si)3P7 can be obtained from P4 and Pred in excellent yields by a safe and simple method and are versatile precursors for the synthesis of imidazoyl phosphinidenes with varying steric demand. The one-step syntheses of imidazoyl phosphinidenes and bis(imidazolyl)–P(I) halides from elemental phosphorus or Na3P7 and (Me3Si)3P7 are described. The heptaphosphides are obtained from P4 and Pred in excellent yields by a safe and simple method. The breakdown of P4 involves the participation of N-heterocyclic carbenes (NHCs) and tBuOH.
Datum: 22.10.2015

The Heavier Analogues of Alkenes: A Theoretical Comparison of Unsaturated Group 15/14 Systems

In this comprehensive study on unsaturated phosphorus compounds of the type R–P=CR2, R–P=N–R, and R–P=P–R, we investigated how the electronic, spectroscopic, and geometric parameters are influenced by different substituents by means of ab initio and DFT methods. The parent systems are studied with highly accurate theoretical methods and used to benchmark DFT methods. The substituent effects are rationalized based on orbital analysis of DFT calculations for phosphaalkenes, iminophosphanes, and diphosphenes in comparison with their analogous alkenes and imines. Theoretical data are also compared to experimental data if available. This study provides a broad picture of the use of DFT methods for unsaturated main group systems. Trends obtained from this study will enable a rational molecule design for selective manipulation of electronic and geometric properties. The theoretical study of phosphaalkenes, iminophosphanes, and diphosphenes in comparison with their alkene and imine analogues, reveals the impact of different substitutions on the electronic, spectroscopic, and structural properties of the phosphorus-containing heteroalkenes.
Datum: 21.10.2015

Reduction of λ5-Phosphinines

A convenient method to easily prepare parent λ3-phosphinine from easily accessible λ5-precursors was developed. A series of λ5-phosphinines bearing heteroatom substituents OMe, SMe, and/or NMe2 at the phosphorus atom were prepared by electrocyclization of phosphahexatrienes generated in situ. Reaction conditions for the synthesis of λ5-phosphinines were optimized. The molecular structure of 1,1-dimethoxy-λ5-phosphinine was determined by an X-ray diffraction analysis. A series of reducing agents were tested in order to prepare λ3-phosphinine. 1,1-Dimethoxy-λ5-phosphinine was reduced by LiAlH4. The method of choice appeared to be the reduction of bis(dimethylamino)-λ5-phosphinine with diisobutylaluminium hydride (DIBAL-H) in 30 % overall yield starting from vinyl ethyl ether. A set of parent λ5-phosphinines bearing OMe, SMe, and/or NMe2 substituents was synthesized. It was shown that they could be readily reduced to parent λ3-phosphinine. The most convenient method appeared to be reduction of readily available λ5-phosphinine featuring the dimethylamino groups. Its congener featuring the diethylamino group does not react under analogous conditions at all.
Datum: 13.10.2015

Formation of a Carbene–Phosphinidene Adduct by NHC-Induced P–P Bond Cleavage in Sodium Tetramesityltetraphosphanediide

The reaction of [Na2(thf)4P4Mes4] (1) (Mes = 2,4,6-Me3C6H2) with 1,3-dimethylimidazolin-2-ylidene (Me2Im) or the corresponding imidazolium iodide ([Me2ImH]I) leads to P–P bond cleavage and formation of the carbene–phosphinidene adduct (Me2Im)PMes (2), which was characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The reaction of [Na2(thf)4P4Mes4] (Mes = 2,4,6-Me3C6H2) with 1,3-dimethylimidazolin-2-ylidene (Me2Im) or the corresponding imidazolium iodide ([Me2ImH]I) leads to P–P bond cleavage and formation of the carbene–phosphinidene adduct (Me2Im)PMes.
Datum: 08.10.2015

The First Coordination Polymers Based on 1,3-Diphosphaferrocenes and 1,1′,2,3′,4-Pentaphosphaferrocenes

Phosphaferrocenes in combination with coinage metal salts proved to be excellent building blocks in supramolecular chemistry for the buildup of oligomeric and polymeric assemblies. The synthesis of a series of novel phosphaferrocenes containing the 1,3-P2C3iPr3 and/or the 1,2,4-P3C2iPr2 ligand is described herein. The self-assembly processes of the 1,3-diphospha-, 1,2,4-triphospha-, and 1,1′,2,3′,4-pentaphosphaferrocenes with CuI halides led to the formation of 1D or 2D polymers. With [Cp*Fe(η5-P2C3iPr3)] (Cp* = η5-C5Me5), infinite chains are formed, whereas with [(η5-P3C2iPr2)Fe(η5-P2C3iPr3)] 1D ladderlike structures are obtained. These are the first polymers containing such a di- and pentaphosphaferrocene, respectively. On the other hand, the use of [Cp*Fe(η5-P3C2iPr2)] leads to the construction of 2D networks with intact sandwich complexes, which is uncommon for this class of complexes. A synthetic approach to a series of iPr-substituted phosphaferrocenes was found. Their self-assembly with CuI halides led to one- and two-dimensional polymers: 1D chains containing the 1,3-diphosphaferrocene, 1D ladderlike structures with the 1,1′,2,3′,4-pentaphosphaferrocene, and 2D meshlike networks bearing the 1,2,4-triphosphaferrocene.
Datum: 08.10.2015

Serendipitous CO- and RhI-Induced ­Coupling of Bidentate Phosphaalkenes with Expulsion of Bis(trimethylsilyl)ketene Leading to RhIII-Coordinated Dianionic Tetradentate Ligands

In the RhCl chelate complexes of C-bis(trimethylsilyl)-P-alkyl(diphenylphosphanyl)aminophosphaalkenes 1 [(Me3Si)2C=PN(R)PPh2; 1a: R = 1-Ada; 1b: R = tBu], the P=C double bonds are preferentially η2-(P,C)-coordinated to RhI, as shown by the structure determination of trans-[RhCl{(Me3Si)2C=PN(R)PPh2}]2 (5a) and by the comparison of the 31P NMR spectra of cis- and trans-[RhCl{(Me3Si)2C=PN(R)PPh2}]2 (5a,b), [RhCl(PPh3){(Me3Si)2C=PN(R)PPh2}] (6a,b), [RhCl(CO){(Me3Si)2C=PN(R)PPh2}] (7a,b) and [(cod)Rh(μ-Cl)2Rh{(Me3Si)2C=PN(R)PPh2}] (8a,b). With excess of [RhCl(cod)]2, the ligand (Me3Si)2C=PN(CH2Ph)PPh2 (1c) forms solid trinuclear complex 10 containing two Rh(Cl)cod moieties attached to the central chelate unit [Rh(Cl)(1c)]: one Rh atom is attached by (terminal) PRh(Cl)cod coordination and the other one by bridging Rh(μ-Cl)2Rhcod. The reactions of the complex [RhCl(CO)(PPh3)2] with ligands 1a or 1b unexpectedly led, with elimination of bis(trimethylsilyl)ketene, to racemic RhIII–chloro complexes [RhCl({Ph2PN(R)P}2C(SiMe3)2)] (11a,b) containing the dianionic tetradentate chelating “bis-PNP” ligands (Me3Si)2C{P(–)N(R)PPh2}2 (12a,b) η4-coordinated to RhIII (CN 5). The CO-induced formation of RhIII complexes 11a and 11b also occurred when 7a and 7b were treated with another equivalent of ligand 1a or 1b, when [RhCl(CO)2]2 was mixed with more than 2 equiv. of 1a or 1b, and even bubbling gaseous CO into a solution containing 6a provided 11a and bis(trimethylsilyl)ketene. The reaction of [RhCl(CO)(PPh3)2] with bidentate phosphaalkene ligands 1 [(Me3Si)2C=PN(R)PPh2; 1a: R = 1-Ada; 1b: R = tBu] leads, with elimination of bis(trimethylsilyl)ketene, to racemic RhIII–chloro complexes [RhCl({Ph2PN(R)P}2C(SiMe3)2)] (11a,b) each containing a dianionic η4-coordinated ligand. CO is essential for the unusual ligand coupling reaction.
Datum: 08.10.2015

Hydride Abstraction and Deprotonation – an Efficient Route to Low Coordinate Phosphorus and Arsenic Species

Treatment of Acenap(PiPr2)(EH2) (Acenap = acenaphthene-5,6-diyl; 1a, E = As; 1b, E = P) with Ph3C·BF4 resulted in hydride abstraction to give [Acenap(PiPr2)(EH)][BF4] (2a, E = As; 2b, E = P). These represent the first structurally characterised phosphino/arsino-phosphonium salts with secondary arsine/phosphine groups, as well as the first example of a Lewis base stabilised primary arsenium cation. Compounds 2a and 2b were deprotonated with NaH to afford low coordinate species Acenap(PiPr2)(E) (3a, E = As; 3b, E = P). This provides an alternative and practical synthetic pathway to the phosphanylidene-σ4-phosphorane 3b and provides mechanistic insight into the formation of arsanylidene-σ4-phosphorane 3a, indirectly supporting the hypothesis that the previously reported dehydrogenation of 1a occurs via an ionic mechanism. Hydride abstraction from a primary phosphine/arsine affords the first examples of secondary phosphino/arsino-phosphonium salts. Subsequent deprotonation provides a novel and high yielding route to phosphine-stabilised phosphinidene/arsinidene. These investigations indirectly support an ionic mechanism for the spontaneous dehydrogenation of the primary arsine.
Datum: 06.10.2015

Iridium(I) Complexes Bearing a Noninnocent PNP-Pincer-Type Phosphaalkene ­Ligand: Catalytic Application in the Base-Free N-Alkylation of Amines with Alcohols

A series of IrI complexes [Ir(L)(PPEP*)] [L = Cl– (3), CO (4), tBuNC (5), PMe3 (6), PPh3 (7)], coordinated with a PNP-pincer-type phosphaalkene ligand bearing a dearomatized pyridine ring (PPEP*), have been prepared and their catalytic properties for the dehydration/condensation of amines with alcohols has been examined. The catalytic reactions successfully proceed under base-free conditions to give N-alkylated amines and their dehydrogenation derivatives (imines). The product selectivity is dependent on L coordinated with Ir(PPEP*). Complexes 4 and 5 that contain π-accepting ligands (CO, tBuNC) form N-alkylated amines as the major products in a closed system using a nitrogen-gas-filled Schlenk tube. In contrast, complex 7 that contain PPh3 as L produces imines as the major products under a nitrogen-gas flow. The reason for the selectivity change depending on L is discussed based on stoichiometric reactions using model compounds of presumed catalytic intermediates. PNP-pincer-type phosphaalkene complexes of IrI bearing a dearomatized pyridine ring have been found to catalyze the dehydration/condensation of amines with alcohols under base-free conditions to afford N-alkylated amines and imines in high yields. The product selectivity can be controlled by the choice of auxiliary ligands (L) as well as the reaction conditions.
Datum: 29.09.2015

The Reaction of Terminal Phosphinidene Complexes [RP–W(CO)5] with Vinylbor­onic Acids: Cycloaddition vs. P–C Bond Formation

The reaction of terminal phosphinidene complexes [RP–W(CO)5] with vinylboronic acids is very sensitive to the presence or absence of solid K3PO4 in suspension in the reaction medium. The products are phosphirane complexes without the salt and secondary vinylphosphine complexes in the presence of the salt. This shift of the reaction pathway is explained by the formation of vinyborates in the presence of potassium phosphate. Terminal phosphinidene complexes react with vinylboronic acid to give the expected phosphirane complexes, but the addition of K3PO4 changes the course of the reaction, and secondary vinylphosphine complexes are obtained instead.
Datum: 14.07.2015

Cobalt(I) and Nickel(II) Complexes of Bis(1,3-diphosphacyclobutadiene) Sandwich Anions

Complexes [(C4Me4)Co(CO)2{Co(P2C2tBu2)2}] (1, C4Me4 = tetramethylcyclobutadiene) and [CpNi{Co(P2C2tBu2)2}(PPh3)] (2, Cp = cyclopentadienyl) were synthesized by transmetalating [Tl(thf)2{Co(P2C2tBu2)2}] with [(C4Me4)Co(CO)2I] and [CpNiBr(PPh3)]. Compounds 1 and 2 were fully characterized by X-ray crystallography, multinuclear NMR, UV/Vis, and IR spectroscopy, and elemental analysis. Their molecular structures show σ-coordination of one phosphorus atom of the [Co(P2C2tBu2)2]– anion to the second metal atom (cobalt or nickel). Time-dependent density functional theory (TD-DFT) calculations were applied to gain insight into the electronic structures and the nature of the electronic transitions observed in the UV/Vis spectra. Cyclic voltammetry studies revealed the similar redox behavior of 1 and 2, which are reversibly oxidized to the corresponding monocations 1+ and 2+ with retention of the dinuclear structures. The cyclic voltammograms furthermore show that 1 and 2 decompose upon reduction with cleavage of the dinuclear structures into the free [Co(P2C2tBu2)2]– anion and further uncharacterized products. Dinuclear diphosphacyclobutadiene complexes have been synthesized by transmetalating the thallium(I) salt [Tl(thf)2{Co(P2C2tBu2)2}] with organometallic cobalt(I) and nickel(II) halides. The structural, spectroscopic, and redox properties of two new bimetallic complexes are presented, and their electronic structures are analyzed by DFT calculations.
Datum: 14.07.2015

Last update: 09.02.2016

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