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European Journal of Inorganic Chemistry - published by Wiley-VCH
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.
The complexes [Mo(O)2(QR)2] [R = cyclohexyl (1), ethylcyclopentyl (2), hexyl (3), and neopentyl (4)] have been obtained in good yields by treatment of [Mo(O)2(acac)2] with 2 equivalents of acylpyrazolone compounds HQR [HQR = 3-methyl-1-phenyl-4-alkylcarbonyl-5-pyrazolone; R = cyclohexyl (HQCy), ethylcyclopentyl (HQEtCp), hexyl (HQHe), neopentyl (HQnPe)]. They were isolated as yellow crystalline solids and characterized spectroscopically [IR, 1H and 13C(1H) NMR] and structurally (X-ray for 2 and 3). The deoxygenation of selected epoxide substrates to alkenes by employing compounds 1 and 3 as catalysts and PPh3 as the oxygen acceptor showed good activities in toluene. The use of the ionic liquid [C4mim]PF6 as solvent gave lower yields, but the resulting catalytic system could be conveniently recycled. The [Mo(O)2(QR)2] derivatives 1 and 3 were also found to be moderately active catalysts for the deoxydehydration of vicinal diols.
Dioxomolybdenum(VI) complexes with acylpyrazolonate ligands have been synthesized, characterized, and tested as catalysts in the deoxygenation of styrene oxide with triphenylphosphane as the oxygen acceptor.
The coordination chemistry of chiral tetradentate dianionic ligands of the diamine-diphenolato and diamine-diolato families having the (R,R)-2,2?-bipyrrolidine core around ZnII was investigated. Reactions with diethylzinc led to complexes of the type [{ONNO}Zn] for most ligands and to bridging dinuclear complexes of the type [?-Lig4(ZnEt)2] for one of the diamine-diolato ligands. Reactions with bis(hexamethyldisilazide)zinc led to complete conversions. Most complexes were obtained as mononuclear complexes. The least bulky Salan ligand, Lig3, led to an equilibrium between mononuclear and dinuclear complexes in noncoordinating solvents. All ligands were found to wrap around the tetrahedral zinc with very high diastereoselectivities supporting predetermined chiral induction from the bipyrrolidine core to the helical ligand wrapping. Molecular structures determined by single-crystal X-ray diffraction for two complexes of the type [{ONNO}Zn] substantiated the predicted ? wrapping of the (R,R)-based ligands. In contrast, representative Salan and diamine-diolato ligands assembled around the trans-1,2-diaminocyclohexane core led to diastereomer mixtures of the corresponding complexes.
Chiral tetradentate dianionic ligands of the diamine-diphenolato and diamine-diolato families based on the (R,R)-2,2?-bipyrrolidine core led to chiral-at-metal complexes of the type [{ONNO}Zn] as single diastereomers supporting a predetermined chiral induction from the bipyrrolidine core to the helical ligand wrapping.
(C2F5)2PNEt2 represents an excellent starting material for the selective synthesis of bis(pentafluoroethyl)phosphane derivatives. The moderately air-sensitive aminophosphane is accessible on a multi-gram scale by treating Cl2PNEt2 with C2F5Li. Treatment with gaseous HCl or HBr yielded the corresponding phosphane halides (C2F5)2PCl and the so far unknown (C2F5)2PBr in good yields. The hitherto unknown (C2F5)2PF was obtained by treating (C2F5)2PBr with excess antimony trifluoride. Treatment of (C2F5)2PCl with Bu3SnH led to the quantitative formation of (C2F5)2PH. Deprotonation formally yielded the (C2F5)2P– anion in a form that was stabilized by coordination to mercury ions to form the complex [Hg{P(C2F5)2}2(dppe)]. An improved high-yielding synthesis of (C2F5)2POH was achieved by treating (C2F5)2PNEt2 with p-toluenesulfonic acid. The gas-phase structures of (C2F5)2PH and (C2F5)2POH were determined by electron diffraction. The vibrational corrections employed in the data analysis of the diffraction data were derived from molecular dynamics calculations. Both compounds exist in the gas phase mostly as C1-symmetric cis,cis conformers with regard the orientation of the C2F5 groups relative to the functional groups H and OH. The presence of a second conformer at ambient temperature is likely in both cases. The refined amounts of dominant conformers are 94(6) and 85(6)?% for (C2F5)2PH and (C2F5)2POH, respectively. The conformational behaviour was further explored by potential energy surface scans based on DFT calculations. Important experimental structural parameters for the most stable conformers are re(P–C)average = 1.884(3) Å for (C2F5)2PH and re(P–C)average = 1.894(4) Å and re(P–O) = 1.582(3) Å for (C2F5)2POH. The different coordination properties of (C2F5)3P, (C2F5)2POH, (CF3)3P and (CF3)2POH were evaluated by complex formation with [Ni(CO)4]: the maximum achievable number of CO ligands substituted by (C2F5)3P is 1, by (C2F5)2POH is 2, by (CF3)3P is 3 and by the smallest ligand (CF3)2POH is 4.
New synthetic routes to a series of bis(pentafluoroethyl)phosphanes have been developed and the structures of two of them, (C2F5)2PH and the phosphinous acid (C2F5)2POH, were studied by gas electron diffraction, making use of molecular dynamics calculations to support data analysis in an improved approach.
Two new polyoxopalladates Na2H3[Pd12(?3-SeO3)8(?4-O)6(?3-O)2Cr]·25H2O (1) and Na8H7[Pd12(?3-SeO3)8(?4-O)8In]3·24H2O (2) have been synthesized by using Cr3+ and In3+ ions as structural directing agents. The two polyoxopalladates have been characterized by single-crystal X-ray diffraction (SXRD), FTIR and UV/Vis spectroscopy, elemental analysis (EA), ESI-MS, and thermogravimetric analysis (TGA). Detailed SXRD analysis combined with the ESI-MS and a collision-induced dissociation (CID) fragmentation study shows that the coordination configurations of the central ions are different; this affects the stability and fragmentation mechanism of the clusters in the gas phase. This approach may help us to understand the dissociation chemistry and the catalysis mechanism of polyoxopalladates.
Two polyoxopalladates {Pd12XIII} have been synthesized by using Cr3+ and In3+ ions as structural directing agents. The coordination configuration of the central metal ions influenced by their ionic radii can affect the cluster stability, as shown by their collision-induced dissociation MS/MS spectra. This approach may help us to understand the stability and dissociation of polyoxopalladates.
The cover picture shows a palladium complex stabilized by an N-heterocyclic carbene bearing two non-rotating alkylfluorenyl substituents. N-heterocyclic carbene ligands of this type are sterically not very crowded, but they can nevertheless be used to prepare remarkably fast Suzuki?Miyaura cross-coupling catalysts. Their efficiency relies on their ability to behave like a ?clamp? that can permanently protect two trans-located coordination sites. Details are discussed in the Short Communication by E. Brenner, D. Matt et al. on p. 2841 ff. For more on the story behind the cover research, see the Cover Profile.
N-Heterocyclic Carbenes Functioning as Monoligating ClampsUnexpectedly, these complexes showed activities equal or superior to those of the best Suzuki? Miyaura catalysts reported to date...This and more about the story behind the cover in the Cover Profile and about the research itself on p. 2841 ff.
Thermal or photodecomposition of the classical free radical generating diazo reagent 2,2?-azobis(2-methylpropionitrile) (AIBN) was used as a source of cyanide anions in the synthesis of copper(I)–cyanide frameworks. The reported methodology utilizes the direct reduction of CuII(aa)(NN)X (aa = deprotonated amino acid, NN = bidentate nitrogen-based ligand, X = Cl or Br) complexes by AIBN/ascorbic acid to yield seven novel coordination networks. Aromatic amines were directly incorporated into 1D CuI–CN chains. In the case of the aliphatic amine tetramethylethylenediamine (TMEDA), a 3D CuI–CN framework was obtained. This novel procedure is mild, applicable to a variety of nitrogen-based ligands, and represents an efficient alternative to currently used hydrothermal or solvothermal methods.
Thermal or photodecomposition of 2,2?-azobis(2-methylpropionitrile) (AIBN) is used as a source of cyanide anions in the synthesis of copper(I)–cyanide frameworks. The reported methodology utilizes the direct reduction of CuII(aa)(NN)X (aa = deprotonated amino acid, NN = bidentate nitrogen-based ligand, X = Cl or Br) complexes by AIBN/ascorbic acid to yield six novel coordination networks.
Well-ordered ultrathin films (UTFs) of {pyrenetetrasulfonate(PyTS)/ZnS}n were fabricated by alternating assembly of 1,3,6,8-PyTS and exfoliated Zn2Al layered double hydroxide (LDH) nanosheets through layer-by-layer (LBL) electrostatic deposition, followed by an effective in situ gas/solid sulfurization reaction with H2S. The assembly process was monitored by UV/Vis spectroscopy, which showed regular stepwise growth of the (PyTS/LDH)n UTFs with consecutive deposition cycles. It is worth noting that the structure of the well-ordered UTFs is retained after the in situ gas/solid sulfurization reaction. Although both (PyTS/LDH)n UTFs and the sulfurized (PyTS/ZnS)n UTFs respond to ethanol at a relatively low operating temperature (70 °C), the (PyTS/ZnS)n UTFs exhibit a much better response, a fact that can be attributed to synergistic interactions between inorganic ZnS and organic pyrene components. Moreover, the well-ordered (PyTS/ZnS)30 UTF exhibits a stronger sensor response to ethanol than to other gases, including NH3, H2, CO, C2H2, and CH4.
{Pyrenetetrasulfonate(PyTS)/ZnS}n ultrathin films have been fabricated by a two-step procedure of layer-by-layer assembly of PyTS with Zn2Al layered double hydroxide, followed by in situ sulfurization with H2S. Gas-sensing measurements of the as-prepared (PyTS/ZnS)n films indicate that they selectively respond to ethanol gas at a relatively low temperature of 70 °C.
The capability of bis(trimethylsilyl)amidoalane to act as a hydride transfer reagent in organolanthanide chemistry was investigated by probing its reactivity toward alkylyttrium complexes. Reaction with Cp*2YMe(thf) led to the isolation of the bimetallic complex Cp*2Y(?-H)2Al(Me)[N(SiMe3)2] (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene), whereas reaction with [Cp*YMe2]3 gave MeAl[N(SiMe3)2]2 as the only isolable hydride transfer product. The dimeric complex [Cp*Y{N(SiMe3)2}(?-H)]2 represents one possible product of the aforementioned reaction that could be structurally characterized. The use of [YMe3]n as the alkylyttrium source led to the isolation of Y[N(SiMe3)2]3, which displays competition between amide and hydride transfer. Finally, the performance of Cp*2Y(?-H)2Al(Me)[N(SiMe3)2] and [YMe3]n in the hydroalumination of 1-octene was tested, and these compounds represent the first rare-earth metal catalysts for this transformation.
YAH: Alkyl/hydrido exchange readily takes place when the yttrium methyl complexes (C5Me5)2YMe(thf), [(C5Me5)YMe2]3, and [YMe3]n are treated with the amidoalane HAl[N(SiMe3)2]2. The resulting heterobimetallics catalyze the addition of the amidoalane across 1-octene, as shown for (C5Me5)2Y(?-H)2Al(Me)[N(SiMe3)2].
The reactions of the metallocene generators Cp?2M(L)(?2-Me3SiC?CSiMe3) [1a-Ti: Cp? = Cp = ?5-cyclopentadienyl, M = Ti, L = none; 1b-Ti: Cp? = Cp* = ?5-pentamethylcyclopentadienyl, M = Ti, L = none; 1c-Ti: Cp?2 = rac-(ebthi) = rac-ethylenebistetrahydroindenyl, M = Ti, L = none; 1a-Zr: Cp? = Cp, M = Zr, L = pyridine; 1b-Zr: Cp? = Cp*, M = Zr, L = none; 1c-Zr: Cp?2 = rac-(ebthi), M = Zr, L = none] with 1,2-bis(4?,4?,5?,5?-tetramethyl[1?,3?,2?]dioxaborolan-2?-yl)acetylene (bPinBA, 2) as a di-heteroatom-substituted alkyne were investigated. A slightly special reaction of 1a-Ti with 2 produced no titanacyclopropene or titanacyclopentadiene, but instead complex 3 was produced by the coupling of two alkyne units with one of the Cp ligands to form a six-membered ring annelated to a five-membered one. The titanocene complexes 1b-Ti and 1c-Ti reacted with 2 to form the titanacylopropenes 4 and 5. The complex 1a-Zr reacts with 2 to the corresponding zirconacyclopropene 6 as a byproduct, in which the pyridine ligand remains coordinated. If the pyridine ligand dissociates, a coupling with a second alkyne yields the zirconacyclopentadiene 7 as the main product. The reaction of the sterically more demanding zirconocene precursor 1c-Zr also yielded the zirconacyclopentadiene 8, whereas 1b-Zr did not react with 2. The complex rac-(ebthi)Ti(?2-bPinBA) (5) reacts with gaseous dry CO2 directly to form the titanafuranone 9. The molecular structures of complexes 5 and 6 were characterised by single-crystal X-ray crystallography.
Group 4 metallocenes and bis(tetramethyldioxaborolanyl)acetylene gave different products: “Cp2Ti” afforded a dihydroindenyl complex. “rac-(ebthi)Ti”, “Cp*2Ti” and “Cp2Zr(py)” led to metallacyclopropenes, whereas “Cp2Zr” and “rac-(ebthi)Zr” yielded metallacyclopentadienes. One of the titanacyclopropenes reacts with CO2 to a titanacyclofuranone.
A novel synthetic route to 4,4?-disubstituted-2,2?:6?,2?-terpyridine ligands by Suzuki–Miyaura cross-coupling was elaborated by synthesizing compounds 4a–5c. The considerable stability of 4-substituted lithium triisopropyl 2-pyridylborates 2a–c, which are less prone to protodeboronation than similarly functionalized neutral boronic acid derivatives, enabled this synthetic route. The terpyridine core structure was further functionalized by exposing 4,4?-dichloroterpyridine (4b) to Suzuki coupling conditions to yield 4,4?-diarylterpyridines 5a–c. Homoleptic FeII complexes 8a–f of the reported terpyridine ligands were formed quantitatively, which demonstrates the lack of steric repulsion of substituents at the 4- and 4?-positions during complexation. The solid-state structures of particular ligands and FeII complexes were analyzed by single-crystal X-ray crystallography. UV/Vis absorption data for the FeII complexes are also provided to complement the results reported here.
A novel synthetic route to terpyridine ligands is reported. Pyridine building blocks are interlinked by Suzuki–Miyaura cross-coupling reactions. The potential of the method is demonstrated by assembling the 4,4?-disubstituted terpyridine ligands shown, which are subsequently converted into their homoleptic FeII complexes.
A DFT/time-dependent DFT (TD-DFT) investigation was conducted on a series of cationic iridium(III) complexes with 2-phenylpyridine (ppyn) derivatives and a diphosphane (PPn) ancillary ligand to shed light on the effects of stereoisomerism and ligand substituents on the photophysical properties. The geometries, electronic structures, lowest-lying singlet–singlet absorptions, vertical singlet–triplet excitations, and triplet–singlet emissions of N,N-cis-[Ir(ppy0)2(PP)]+ (1), N,N-trans-[Ir(ppy0)2(PP)]+ (2) and their derivatives were investigated with DFT-based approaches [ppy0 = 2-phenylpyridine, PP = 1,2-bis(diphenylphosphanyl)ethene]. The complex N,N-trans-[Ir(ppy2)2(PP2)]+ (3b) shows high quantum phosphorescence efficiency (?PL) of 91?%, whereas an extremely low ?PL (<1?%) was observed for N,N-trans-[Ir(ppy4)2(PP1)]+ (2d). To clarify this behavior, the S1–Tn splitting energy (?E?S?1–T?n), the transition dipole moment (??S?1) upon the S0?S1 transition, and the energy gap between the triplet metal-to-ligand charge transfer (3MLCT) ?–?* and triplet metal-centered (3MC) d–d states (?EMC–MLCT) were calculated. A drastically small ?E?S?1–T?3 and large ??S?1 for 3b (<0.05 eV and 1.38 D, respectively), compared to those for 2d (>0.2 eV and 1.26 D, respectively), were found to be closely linked to the substituents on the ppyn ligands. The remarkably small ?E?S?1–T?3 and similar ??S?1 for N,N-cis 1c (<0.05 eV and 1.41 D, respectively), compared to those for N,N-trans 2c (>0.1 eV and 1.42 D, respectively), could be attributed to the effects of the trans–cis structural isomerism. On the basis of these parameters, the higher ?PL of 3b with respect to that of 2d was explained, and 1c, 1d, 2b, and 2e were considered to have better physical properties than the experimentally synthesized complexes 2, 2d, and 3b. The newly designed 1c, 1d, 2b, and 2e are expected to be highly emissive in the blue-green region for light-emitting electrochemical cell (LEC) applications.
The N,N-trans and N,N-cis isomers of [Ir(ppy0)2(PP)]+ (ppy0 = 2-phenylpyridine ligand, PP = diphosphane ligand) have markedly different photophysical properties, which were investigated by a DFT/time-dependent DFT (TD-DFT) approach. Their different quantum phosphorescence efficiencies (?PL) are interpreted with their different radiative (kr) and nonradiative (knr) rates.
The first terminal organometallic alkylphosphanylidenetantalum(V) complexes [Cp*Ta{1,2-(NSiMe3)2C6H4}(PR)] were obtained with cyclohexyl (2) and isopropyl groups (3) at phosphorus, whereas adamantyl and tert-butyl substituents resulted in the formation of the paramagnetic tantalum(IV) complex [Cp*Ta{1,2-(NSiMe3)2C6H4}Cl] (4). DFT studies showed that the terminal cyclohexyl and isopropyl phosphanylidene complexes are stable towards dimerization and dissociation.
The first terminal organometallic alkylphosphanylidenetantalum(V) complexes are obtained with cyclohexyl and isopropyl groups at phosphorus, whereas adamantyl and tert-butyl substituents result in the formation of a paramagnetic tantalum(IV) complex. DFT studies show that the terminal cyclohexyl and isopropyl phosphanylidene complexes are stable towards dimerization and dissociation.
We demonstrate that the particle sizes in cyano-bridged coordination polymers consisting of NiII–C?N–FeII units are precisely controlled by changing the amount of chelating agent, sodium citrate. With an increase in the amount of chelating agent added, the average size of the particles gradually increases from 20 to 350 nm with retention of a well-defined cubic shape. Furthermore, the use of different Fe sources expands the possible control range up to 500 nm.
The particle sizes in cyano-bridged coordination polymers consisting of NiII–C?N–FeII units are precisely controlled from 20 to 500 nm by changing the amount of sodium citrate added as a chelating agent and/or by using a different Fe source. Our synthetic concept is widely applicable to other coordination polymers, which would be beneficial to various applications in the future.
Perfluoroarylation of a known iron(II) diiodoclathrochelate precursor and its new n-butylboron-capped hexaiodomacrobicyclic analog with pentafluorophenylcopper(I) gave the first iron(II) cage complexes with inherent perfluoroaryl substituent(s). The complexes synthesized were characterized by elemental analysis, MALDI-TOF mass spectrometry, IR, UV/Vis, 1H, 11B, 19F, and 13C{1H} NMR spectroscopy, and X-ray crystallography. The encapsulated iron(II) ions in the X-rayed hexaiodo- and di- and hexa(pentafluorophenyl)ated iron(II) clathrochelates are located almost in the centers of their FeN6 coordination polyhedra. The geometry of the hexaiodoclathrochelate precursor is trigonal prismatic (TP, distortion angle ? = 4.5°), whereas the perfluoroarylated iron(II) clathrochelates are intermediate between a TP and a trigonal antiprism (TAP) (? ? 25°). This rotation and expansion from TP to TAP polyhedra causes horizontal spreading, and the heights h decrease from 2.40 to 2.33–2.35 Å. Anodic ranges of the cyclic voltammograms (CVs) for the pentafluorophenylated iron(II) clathrochelates contain one-electron waves of the metal-centered Fe2+/3+ oxidation, which are quasireversible in the cyclic voltammetry (CV) timescale. The potentials for the mono- and difunctionalized clathrochelates are only slightly different, as a result of steric hindrance between two pentafluorophenyl substituents in the same chelate ribbed fragment decreasing their conjugation with the polyazomethine clathrochelate framework and lowering the electronic effects. The cathodic ranges of these CVs contain irreversible waves for encapsulated metal-centered Fe2+/+ reduction to anionic forms of the cage complexes that are unstable on the CV timescale.
Iron(II) clathrochelates with two and six inherent pentafluorophenyl substituents were obtained by copper-promoted perfluoroarylation of their iodine-containing macrobicyclic precursors and characterized by analytical and spectral methods and X-ray diffraction.
New mixed-valence CuI–CuII 1D coordination polymers of the structure [CuI2CuIIX2(Pip-dtc)2(CH3CN)2]n [Pip-dtc = piperidine-1-carbodithioate; X = Br (1a), I (1b)] containing a dithiocarbamate derivative have been synthesized and structurally characterized by X-ray diffraction. The 1D infinite chains were formed from mononuclear copper units [Cu(Pip-dtc)2] connected by bromido- or iodido-bridged copper dinuclear units that include acetonitrile ligands {i.e., [Cu2X2(CH3CN)2]}. Evaluation of the magnetic properties of 1a and 1b revealed that these complexes displayed relatively strong antiferromagnetic interactions [J = –20.4 cm–1 (1a) and J = –18.8 cm–1 (1b)] between unpaired electrons of the copper(II) ions through the dinuclear halido–copper(I) units. Impedance spectroscopy revealed that complexes 1a and 1b exhibit intriguing semiconducting properties at activation energies of Ea = 0.78 eV (1a) and Ea = 0.62 eV (1b). Coordination polymers 1a and 1b were then adopted as the sensitizing material in dye-sensitized solar cells (DSSCs).
New halido-bridged mixed-valence CuI–CuII coordination polymers with 1D infinite chain structures have been synthesized and structurally characterized The complexes show a relatively strong antiferromagnetic interaction and interesting semiconducting behavior. These coordination polymers were applied as sensitizing materials for DSSCs.
5-Cyanotetrazole readily forms from (CN)2 and HN3. The coordination abilities of the 5-cyanotetrazolate anion N4CCN– (ctz) towards CuII ions were examined and a series of complexes and coordination polymers were synthesized and characterized by single-crystal structure analyses: PPh4[Cu(ctz)3] (1), [Cu(ctz)2(bipy)] (2, bipy = 2,2?-bipyridine), [CuCl(py)4](ctz)·2py (3, py = pyridine), [Cu2(ctz)6Cu(CH3CN)2(H2O)2]·2CH3CN (4a), [Cu2(ctz)6Cu(H2O)3{(CH3)2CO}]·3(CH3)2CO (4b), [Cu(ctz)2(py)4] (5), [Cu2(ctz)4(bipy)2] (6) and [Cu2(ctz)2(tpm)2(NO3)]NO3 [7, tpm = tris(pyrazol-1-yl)methane]. As ctz is a multidentate linker, additional neutral coligands such as monodentate py, bidentate bipy and tridentate tpm ligands were used to avoid the formation of noncrystalline polymers. The structures of 1–7 reflect the versatile coordination abilities of ctz in the various types of coordination environments of the CuII ions and dimensionalities of the linkages. The structures represent 1D chain motifs (1, 2 and 3), 2D layered structures (4a and 4b), mononuclear (5) and dinuclear complexes (6 and 7). Magnetic coupling phenomena were detected by susceptibility measurements of 1, 4a, 6 and 7, which were fitted to the magnetic models according to antiferromagnetic spin-pairing of two S = 1/2 systems (Bleaney–Bowers) for 6 (J = –0.53 cm–1) and 7 (J = –2.91 cm–1), to the ferromagnetic high-temperature series expansion based on the Baker 1D (S = 1/2) chain model for 1 (J = +14.4 cm–1) and to the Néel model of ferrimagnetism for 4a. The diverse magnetic interactions between the Cu2+ sites are communicated by the bridging ctz anions.
Cyanotetrazolate (ctz) is a versatile ligand towards CuII ions and allows different kinds of linkage. Eight complexes and coordination polymers are presented with structures representing 1D chain motifs, 2D layered structures, mononuclear and dinuclear complexes. The complexes show different magnetic coupling phenomena at low temperatures.
Donor–acceptor interactions play a dominant role in descriptions of various chemical systems. The interactions of main-group Lewis bases with main-group Lewis acids has attracted interest for many years. In this article, donor–acceptor interactions in NHC–EX3 (NHC = normal and abnormal N-heterocyclic carbene; E = B, Al, Ga; X = H, F, Cl, OH, NH2, CH3, CF3) adducts have been investigated within the realms of DFT and atoms-in-molecules (AIM) theory. Substituents attached to the E atom have a profound effect on the strength and dissociation energies of the NHC–E bond. AIM analysis suggests that these donor–acceptor bonds have significant covalent character, which follows the order Al < Ga < B.
Donor–acceptor bonds in the complexes of normal and abnormal N-heterocyclic carbenes with tricoordinate group 13 elements (B, Al and Ga) have been studied by quantum chemistry. The substituents attached to the group 13 atoms are found to have a profound effect on the strengths of the donor–acceptor bonds.
The syntheses of several cobalt diglyoximate complexes connected by one or two aluminum bridges are described. The aluminum centers are supported by tunable tetradentate diamine bisphenoxide ligands. Electrochemical investigations revealed that the number of aluminum bridges and the nature of the substituents on the phenoxide ligands significantly affect the cobalt reduction potentials. The present aluminum–cobalt compounds are electrocatalysts for proton reduction to hydrogen at potentials negative relative to those of the boron- and proton-bridged analogs. The reported synthetic strategies allow modulation of the reduction potentials and the secondary coordination sphere interactions by tuning the ancillary ligands bound to aluminum.
Cobalt diglyoximate complexes connected by aluminum bridges were synthesized. The redox chemistry of these species is dependent on the number of aluminum centers and the nature of the ancillary ligand coordinated to aluminum. Proton reduction to hydrogen was observed and compared to BF2- and proton-bridged analogs.
N-(Quinoline-8-yl-aryl)benzenesulfonamides 1–6 were successfully synthesized by the reaction of 8-aminoquinoline and various benzenesulfonyl chlorides. Then, half-sandwich ruthenium complexes 7–12 were prepared from the reactions of 1–6 with [RuCl2(p-cymene)]2. The synthesized compounds were characterized by NMR and FTIR spectroscopy and elemental analysis, and compounds 8 and 9 were further analyzed by X-ray diffraction. The complexes were screened for their efficiency as catalysts in the transfer hydrogenation of acetophenone derivatives to phenylethanols in the presence of KOH with 2-propanol (as hydrogen source) at 82 °C, and they all showed good activity. Complexes 10 and 12 were the most active (turnover frequency values: 703 and 734 h–1, respectively).
A series of new half-sandwich RuII complexes containing sulfonamide ligands were synthesized and characterized by NMR and FTIR spectroscopy and elemental analysis, and two of the complexes were further analyzed by X-ray diffraction. We investigated the catalytic activity of these complexes in the transfer hydrogenation of a few acetophenone derivatives with the use of 2-propanol in the presence of base.
Six MnIII complexes of general formula [Mn(L)XY], in which L is a dideprotonated Schiff base ligand N,N?-bis(pyridoxylidene)ethylenediamine (L1H2 or pydxen) or N,N?-bis(pyridoxylidene)-1,3-propanediamine (L2H2 or pydxpn), X = Cl, N3, NCS, and Y = H2O, MeOH, EtOH, and another MnIII compound [Mn(L1)(H2O)2]Cl have been synthesized. The structures of five of the complexes were determined by single-crystal X-ray diffraction studies. The compounds show a quasireversible MnIII/MnII couple at ca. 0 V (vs. Ag/AgCl) and two to three overlapping oxidations at 1.0–1.3 V, which are assigned to MnIII/MnIV oxidation and ligand (phenolate) oxidation. The redox potential of the phenolate moiety reported here is very similar to the Yz/Yz·+ potential of photosystem II (PS II, Yz = tyrosine). Spectrochemical studies and DFT calculations support this assignment. The DFT calculations also show that there is considerable covalence in the metal–ligand bonds and the covalence increases with the oxidation state of the central metal ion. The geometry of the metal ion is found to be dependent on the oxidation state as well as spin state of the metal ion, the nature of the N,O-donor ligand used as model, and solvation effects. In silico stepwise one and two electron oxidation of a model pydxen-type complex shows strengthening of the metal–ligands interactions, but three-electron oxidation could significantly weaken one of the Mn–O bonds, which might trigger splitting into a diphenoxyl diradical species and a transient MnIV complex, in agreement with the experimental results.
MnIII compounds of N,N?-bis(pyridoxylidene)ethylenediamine and N,N?-bis(pyridoxylidene)-1,3-propanediamine show a quasireversible MnIII/MnII couple at ca. 0 V (vs. Ag/AgCl) and two to three overlapping oxidations at 1.0–1.3 V, which are assigned to MnIII/MnIV and phenolate oxidations.
Recently, it has been demonstrated that the insertion of CO2 into iridium hydrides is a crucial step in the catalytic conversion of CO2 and H2 into formic acid. We and others have elucidated the mechanism by which CO2 inserts into six-coordinate iridium(III) trihydrides supported by pincer ligands; these complexes are very active catalysts for CO2 hydrogenation. However, it has also been demonstrated that five-coordinate iridium(III) dihydrides can react with CO2 and catalyze both thermal and electrochemical CO2 hydrogenation. In this work, we study the mechanism of CO2 insertion into pincer-supported five-coordinate iridium(III) dihydrides and four-coordinate iridium(I) hydrides using density functional theory. The mechanisms differ slightly between the two cases. Insertion into the five-coordinate species is a multistep process involving initial CO2 precoordination, whereas insertion into the four-coordinate species proceeds via a single step with no prior CO2 coordination. Both of these mechanisms are different from the pathway that was recently proposed for CO2 insertion into six-coordinate iridium(III) trihydrides. In addition, a complete pathway for catalytic CO2 hydrogenation using a five-coordinate iridium(III) dihydride has been calculated.
The insertion of CO2 into iridium hydrides has been proposed as a crucial step in the iridium-catalyzed hydrogenation of CO2. We used DFT to explore the mechanism of CO2 insertion into five-coordinate iridium(III) dihydrides and four-coordinate iridium(I) monohydrides with pincer ligands, and also calculated the catalytic cycle for thermal CO2 hydrogenation starting from an iridium(III) dihydride.
A nitride complex [K(thf)2]2[{(O3)Nb}2(?-N)2] (2), prepared from [K(DME)]2[{(O3)Nb}2(?-H)4] (1) and N2, was protonated with 2,6-lutidinium chloride to yield ammonia and [(O3)NbCl3]– (3), where H3[O3] = tris(3,5-di-tert-butyl-2-hydroxy phenyl)methane. The reaction of 3 with KBHEt3 regenerated [K(DME)]2[{(O3)Nb}2(?-H)4] (1), thereby completing a synthetic cycle for the conversion of N2 to NH3. Alkylation of 2 with methyl iodide led to formation of [K(thf)][{(O3)Nb}2(?-N)(?-NMe)] (4) and [{(O3)Nb}2(?-NMe)2] (5). Treatment of 5 with pyridine afforded a terminal imide complex [(O3)Nb=NMe(py)2] (6). The imide monomer 6 reacted with CO2 to give [(O3)Nb{(MeN)2CO}(py)] (7) and [{(O3)Nb}2(?-O)2] (8) in a 2:1 ratio, while the reaction of 6 with p-TolNCO gave an asymmetric ureate complex [(O3)Nb{p-TolNC(O)NMe}(py)] (9).
The niobium nitride complex prepared from N2 was protonated to generate NH3, while the reaction with methyl iodide gave the methyl imide complex. Exposure of the imide complex to CO2 gave the ureate complex along with the oxo-bridged dinuclear complex.
An attempt to prepare Tmp-C(NDipp)2Li by treatment of lithium tetramethylpiperidide (Li-Tmp) with N,N?-bis(2,6-diisopropylphenyl)carbodiimide (Dipp-N=C=N-Dipp) failed, and ether degradation occurred instead, allowing the isolation of a few crystals of O=CH–CH=C(NH-Dipp)2 (1) after hydrolytic work-up. We then investigated calcium and strontium compounds. Metalation of PrisoH [Priso = iPr2N–C(N-Dipp)2] with [(thf)2Ca{N(SiMe3)2}2] in refluxing hexane for 18 h yielded [{(Me3Si)2N}(thf)Ca(Priso)] (2). At room temperature, very few crystals of [Ca(Priso)2]·hexane (3) precipitated after several months from a saturated hexane solution of 2. KN(SiMe3)2 was added to a THF solution of [(thf)4CaI2] and PrisoH and heated to 60 °C for several hours yielding [(thf)Ca(Priso)(?-I)]2 (4). Metalation of PrisoH with [(thf)2Sr{N(SiMe3)2}2] led to formation of [Sr(Priso)2] (5) regardless of the applied stoichiometry. The reaction of N,N?-bis(2,6-diisopropylphenyl)benzamidine with KN(SiMe3)2 and [(thf)4CaI2] in THF followed by recrystallization from 1,2-dimethoxyethane (dme) solution yielded [(dme)Ca{(Dipp-N)2C–Ph}2] (6). The molecular structures of these compounds are discussed and compared with those of other encumbered complexes of divalent metal ions.
In N,N?-bis(diisopropylphenyl)amidinates and guanidinates of calcium the metal center is effectively shielded. Therefore drastic reaction conditions are required, with the disadvantage that side reactions such as ether cleavage and subsequent reactions also occur.
The synthesis of the classical, neutral donor–acceptor adducts Ph2MeP–/Ph3P–/Ph3As–Al(ORF)3 and H2O–Al(ORF)3 [1, 2, 3, 4, ORF = OC(CF3)3] is reported. The intermediate H2O–Al(ORF)3 (4) was generated by substitution of PhF in PhF–Al(ORF)3 with H2O and was analyzed in a long-term NMR study over 22 days. This Brønsted acidic system was used in orienting experiments to protonate phosphanes such as PMePh2, PPh3, PCy3, P(tBu)3, and PCy2[2,4,6-(iPr)3C6H2]. Depending on the use of one or two equivalents of PhF–Al(ORF)3, the new weakly coordinating anions [(RFO)3Al(?-OH)Al(ORF)3]– or [HOAl(ORF)3]– were obtained. However, in dependence of the steric bulk of the phosphanes, stable and unreactive R3P–Al(ORF)3 adducts were also observed in the NMR experiments. The absolute acidity of the key H2O–Al(ORF)3 adduct was evaluated by the relaxed COSMO cluster-continuum (rCCC, COSMO = conductor-like screening model) model in fluorobenzene solution. For a 0.001 M solution of H2O–Al(ORF)3, the medium acidity resulted as –986 kJ?mol–1 or a pHabs value of 173. Long-term hydrolysis of H2O–Al(ORF)3 (4), probably to give HORF and HOAl(ORF)2 followed by trimerization, gave [HOAl(ORF)2]3 (10), which was identified by X-ray diffraction.
Small donor ligands such as Ph2MeP, Ph3P, Ph3As, or even H2O form classical donor–acceptor adducts with the Lewis superacid Al(ORF)3 [RF = C(CF3)3]. FLP-like (FLP = frustrated Lewis pair) combinations of this Lewis acid, phosphanes, and water then lead to [HPR3]+ and two new weakly coordinating anions [HOAl(ORF)3]– and [(FRO)3Al(?-OH)Al(ORF)3]–. The absolute acidity of H2O–Al(ORF)3 is evaluated.
Properties of the EuIII/EuII redox couple, in the presence of one of a group of different ligands of ligands, were investigated using several electrochemical methods. Ligands used in this study included cyclodextrins, polyazamacrocycles and poly(aminocarboxylates). The poly(aminocarboxylate) containing ligands currently used as MRI contrast agents (DTPA, DOTA) as well as newly developed ligands [1,4-DOTA(GAC12)2, 1,7-DOTA(GAC12)2] with potential use as MRI contrast agents were studied. Cyclic voltammetry, phase sensitive AC voltammetry, DC polarography and highly effective electrochemical impedance spectroscopy were utilised to elucidate the mechanism of the reduction/oxidation of the Eu ion in the presence of these compounds. Stability constants of the EuIII and/or EuII complexes and heterogeneous rate constants of the charge transfer were determined. Theoretical calculations of molecular volumes and diffusion coefficients were performed as well.
CV, AC voltammetry, DC polarography and impedance spectroscopy were utilized to elucidate the mechanism, stability constants and heterogeneous rate constants of the charge transfer of the reduction/oxidation of the EuIII/EuII ion pair in the presence the newly developed ligands 1,4-DOTA(GAC12)2 and 1,7-DOTA(GAC12)2 with potential use as MRI contrast agents.
The symmetry-forbidden cyclometalation of (silox)2W=NtBu (1, silox = OSitBu3) to (silox)(tBuN)W(H)(?O,?C-OSitBu2CMe2CH2) (2) was investigated by kinetics [?H‡ = 19.2(9) kcal/mol; ?S‡ = –23(3) eu; ?G‡(25 °C) = 26.1(10) kcal/mol], isotopic labeling {[D54]1 ? [D54]2; kH/kD = 2.7(4)}, and equilibrium studies [?H° = –6.7(3) kcal/mol; ?S° = –12.1(8) eu; ?G°(25 °C) = –3.1(4) kcal/mol]. The crystal structure of 2 reveals a pseudo-square-pyramidal structure that can be viewed as a distorted tetrahedron with the W–H and W–C bonds occupying one site. The addition of H2 (or D2) to 1 proceeds similarly to afford (silox)2(tBuN=)WH2 (3), and the addition of H2 to 2 also affords 3, but labeling experiments show that it proceeds via 1. Phosphane bases with cone angles < 160° trigger the cyclometalation of 1 to 2 in < 5 min, and PMe3 catalyzed the dihydrogen addition to 1. Quantum mechanics/molecular mechanics (QM/MM) calculations support the experimental findings and show that Lewis bases promote ?/? mixing. The experimentally observed intermediate (silox)2(tBuN=)WPMe3 (1-PMe3) has a (dyz)2 (i.e., ?2) ground state in contrast to the (d?z?2)2 (i.e., ?2) configuration of 1. The ?/? mixing circumvents the constraints of orbital symmetry for both cyclometalation and dihydrogen addition.
The symmetry-forbidden cyclometalation of (silox)2W=NtBu (1, silox = OSitBu3) to (silox)(tBuN)W(H)(?O,?C-OSitBu2CMe2CH2) (2) and the oxidative addition of dihydrogen to give (silox)2(tBuN=)WH2 (3) are catalyzed by phosphane bases with cone angles < 160°. Quantum mechanics/molecular mechanics (QM/MM) calculations support the experimental findings and show that Lewis bases promote ?/? mixing.
The structural organization and magnetic properties of MnIII complexes with meso-tetraphenylporphyrin (TPP), bis(3,5-di-tert-butylsalicylidene)ethylenediamine (tBuSalen), and bis(salicylidene)ethylenediamine (Salen) capping ligands assembled with phosphinate ligands such as H2PO2–, PhHPO2– and Ph2PO2– have been investigated. The structural organization and, thus, the magnetic properties in this series depends on the nature of both the capping and bridging ligands. The hypophosphite ion (H2PO2–) and the diphenylphosphinate ion (Ph2PO2–) act as bridging ligands to form 1D polymeric structures [{Mn(TPP)O2PH2}2·H2O·EtOH]n and [Mn(Salen)O2PPh2]n, among which only the former presents single chain magnet behaviour; the pronounced nonalignment of the anisotropy axes explains the absence of such behaviour in the latter. The phenylphosphinate ion (PhHPO2–) and the diphenylphosphinate ion (Ph2PO2–) act as monodentate ligands in the complexes with tBuSalen and TPP as capping ligands, respectively. The diphenylphosphinate ion acts as both a bidentate ligand and charge-compensating anion in [Mn2(tBuSalen)2(O2PPh2)(EtOH)2+(Ph2PO2–)·H2O].
The synthesis of MnIII complexes capped by tetradentate ligands and assembled by phosphinate ligands is reported. The phosphinate coordination mode is influenced by the steric hindrance of both the phosphinate and the tetradentate ligands. Two 1D polymeric structures have been obtained, one of which presents single chain magnet (SCM) behaviour.
A new pyridine-substituted dithiolene complex, PPh4[Au(4-pdddt)2] (3), was prepared and characterised. Cyclic voltammetry shows three redox processes corresponding to the interconversion between dianionic, monoanionic, neutral and cationic states, as often presented by this type of bis(dithiolene) complexes. However, the last oxidation process in this compound leads to a polymerised species obtained as an electrodeposited film. By potentiostatic electrodeposition, thin films of either the neutral gold complex, [Au(4-pdddt)2] (4), or the polymerised cationic species can be obtained. Both films absorb strongly in the NIR region and have properties consistent with the incorporation of the intact metal bis(dithiolene) complex. A mechanism for polymerisation through formation of S–S interligand bonds is proposed.
Pyridine-substituted dithiolene gold complex [Au(4-pdddt)2] shows three redox processes corresponding to the interconversion between dianionic, monoanionic, neutral and cationic states, the last one corresponding to a polymerised species obtained as an electrodeposited film.
For the first time, single crystals of KPbBP2O8 with sizes up to 18?×?13?×?6 mm have been grown from a stoichiometric mixture of its components by the top seed growth method. The crystal structure was determined from single-crystal X-ray data: tetragonal, space group I$\bar {4}$2d, a = 7.1464(7) Å, c = 13.8917(16) Å, Z = 4. It exhibits an isolated [BP2O8]3– unit that is built from nearly ideal tetrahedral BO4 and PO4 groups, which are connected to each other alternatively by corner-sharing O atoms to make a 12-membered ring. Transmission spectroscopy illustrates that the UV cutoff edge is at approximately 235 nm. Furthermore, IR spectroscopy, thermal analysis, and second-harmonic generation (SHG) measurements were also performed on the reported material.
KPbBP2O8 is synthesized and its structure is determined by single-crystal X-ray diffraction. Thermal and XRD analysis show that KPbBP2O8 melts congruently. IR and UV/Vis spectroscopy and second-harmonic generation measurements are also performed on the reported material.
The evaluation of a new azacrown ether ligand bis{[3-(pyridin-4-yl)-1H-pyrazol-1-yl]methyl}diaza-18-crown-6 (b3pd), which contains pendant p-pyridylpyrazole arms connected by diaminomethane linkers, identified a tendency to undergo retro-Mannich fragmentation in the presence of transition-metal ions. However, treatment of b3pd with potassium perchlorate or potassium iodide prior to complexation with transition-metal ions imparted a resistance to fragmentation, such that crystallisation of coordination polymers from concentrated solutions after several weeks was possible. Four solid-state structures containing Kb3pd were isolated: a perchlorate salt (1), a divalent manganese 1D coordination polymer [Mn(Kb3pd)(DMF)4]·2ClO4·I3 (2, DMF = N,N-dimethylformamide), a cuprous 2D coordination network [Cu2(Kb3pd)2(I3)(I)3]·3H2O (3) and a cuprous 1D coordination polymer [Cu(Kb3pd)(I)2] (4). Additionally, the retro-Mannich process was investigated by in situ FTIR spectroscopy, mass spectrometry, crystallography and by the isolation of a cobalt complex ligated by a partially fragmented ligand, mono{[3-(pyridin-4-yl)-1H-pyrazol-1-yl]methyl}diaza-18-crown-6 (m3pd). The composition of the cobalt complex was found to be [CoCl3(Hm3pd)]·H2O (5).
Diaza-18-crown-6 ligands functionalised with diaminomethane linkers are unstable in the presence of selected divalent transition-metal ions. Pretreatment of the ligands with potassium salts prevents degradation by blocking the central coordination region. Iodide redox chemistry also affects the coordination-polymer motif.
The ambiphilic and small-bite-angle diphosphanylborane ligands Ph2PCH(PPh2)CH2B(C8H14) (2) and Ph2PCH2CH[B(C8H14)]PPh2 (3) containing the Lewis acidic 9-boranorbornyl group B(C8H14) have been prepared in one step by regioselective anti-Markovnikov hydroborations of 1,1-bis(diphenylphosphanyl)ethylene and 1,2-bis(diphenylphosphanyl)ethylene with 9-borabicyclo[3.3.1]nonane (9-BBN) under relatively drastic reaction condition. The coordination properties of Ph2PCH2CH2B(C8H14) (1) and the newly prepared 2 and 3 towards the tungsten nitrosyl fragment {WNO}6 have been studied structurally and spectroscopically. Herein, we report the cis and trans tungsten nitrosyl complexes cis-[W(CO)2(1)2(NO)(Cl)] (cis-4a), cis-[W(CO)2(1)2(NO)(H)] (cis-4b), trans-[W(CO)2(1)2(NO)(Cl)] (trans-4a), trans-[W(CO)2(1)2(NO)(H)] (trans-4b), cis-[W(CO)2(2)(NO)(Cl)] (cis-5a), cis-[W(CO)2(2)(NO)(H)] (cis-5b), cis-[W(CO)2(3)(NO)(Cl)] (cis-6a), cis-[W(CO)2(3)(NO)(H)] (cis-6b), which were readily obtained from straightforward ligand-substitution reactions of the tungsten carbonyl nitrosyl precursor [W(NO)(CO)4(ClAlCl3)] in tetrahydrofuran. The crystal structures of the tungsten chloride complexes cis-4a, trans-4a, and cis-5a revealed that the trialkyl boron centers are free pendants in the secondary coordination spheres, whereas in the hydride complexes trans-4b, cis-5b, and cis-6b the hydride ligand trans to the nitrosyl ligand is ? coordinated to the tethered B(C8H14) group and form three-center, two-electron (3c–2e) W–H–B bonds, which were observed in their crystal structures. The authenticity of the 3c–2e W–H–B bond in the tungsten hydride complex cis-5b was further checked by a DFT structural optimization and natural bond order (NBO) analysis.
The coordination properties of phosphanylborane ligands in newly synthesized tungsten carbonyl nitrosyl complexes are explored by multinuclear NMR and IR spectroscopy, single-crystal X-ray structure analyses, and DFT calculations.
The new carbodiimide compound La3Cl(CN2)O3 was obtained by a solid-state metathesis reaction from LaOCl and Li2(CN2) at 750 °C in a fused tube. Differential scanning calorimetry of the reaction mixture was performed. The crystal structure of La3Cl(CN2)O3 was determined by single-crystal X-ray diffraction studies (space group Cmcm, No. 63). The luminescent properties of the Eu3+- and Tb3+-doped compounds are reported.
The new luminescent material La3Cl(CN2)O3:Ln 5 mol-% (Ln = Eu3+ or Tb3+) was successfully synthesized by a simple reaction of LaOCl with Li2CN2 (+ LnCl3).
Binding NiII to the terminal amine of a peptide depresses totally its nucleophilic character as measured by the rate constant of the reaction of the peptide with 4-nitrophenyl acetate. The structure of NiII(GGGGG) in aqueous solutions was determined by this technique. The results indicate that the ratio of complexes in which the nickel is bound to four deprotonated peptide nitrogen atoms to those in which the nickel is bound to the terminal amine and three deprotonated peptide nitrogen atoms increases as the pH increases. At pH 9.0, this ratio is approximately 1.
We measured the nucleophilic properties of the terminal amine of a Ni(peptide) complex as a tool to elucidate the ligation sites of the cation.
The facile two-electron reduction of the phosphaalkyne tBuC?P by the UIII cyclopentadienyl–pentalene mixed-sandwich complex [U(?5-C5Me5){?8-C8H4(SiiPr3)2}] is reported. A single-crystal X-ray structural analysis of the diuranium(IV) product [(U{?5-C5Me5}{?8-C8H4(SiiPr3)2})2(?-tBuCP)] shows that it contains a slightly unsymmetrical, bridging ?-?2:?1-ligated phosphaalkene dianion.
The two-electron reduction of the phosphaalkyne tBuC?P by the UIII mixed-sandwich complex [U(?5-C5Me5){?8-C8H4(SiiPr3)2}] yields the diuranium(IV) product [(U{?5-C5Me5}{?8-C8H4(SiiPr3)2})2(?-tBuCP)], which contains a ?-?2:?1-ligated phosphaalkene dianion.
Hydrolysis of half-sandwich-type platinum metal cations with the general formula [M(?6-arene)(H2O)3]2+ {M = Ru, Os; ?6-arene = benzene, toluene, 1-methyl-4-isopropylbenzene (p-cym), or 1,3,5-triisopropylbenzene (tri-iPr)} or [Ir(?5-Cp*)(H2O)3]2+ (Cp* = pentamethylcyclopentadienyl anion) was studied in aqueous solution in the presence of 0.20 M KNO3 or KCl as a background electrolyte to explore the effects of the type of metal ion, the moderately coordinating monodentate chloride ion, and the electron-donating ability of the arene ligand. Replacement of Ru by Os enhances the formation of the biologically less-active, triple hydroxido-bridged dimer, [{M(?6-arene)}2(?2-OH)3]+, whereas in the presence of Cl– complete hydrolysis is suppressed owing to the formation of various chlorido and mixed chlorido/hydroxido species as intermediates. A linear relationship was found between the stability constants of the [{Ru(?6-arene)}2(?2-OH)3]+ complexes in the presence of arenes with different electron-donating abilities and various atomic and molecular parameters of the corresponding [Ru(?6-arene)(H2O)3]2+ cations; the triisopropylbenzene derivative was the most resistant to hydrolysis. The results of this study may help in rationalizing the bioactivity of anticancer half-sandwich metal complexes and can contribute to the rational design of metal compounds with increased biological activity.
The hydrolytic properties of half-sandwich [M(?6-arene)(H2O)3]2+ (M = Ru, Os; ?6-arene = benzene, toluene, 1-methyl-4-isopropylbenzene, 1,3,5-triisopropylbenzene) or [Ir(?5-Cp*)(H2O)3]2+ (Cp* = pentamethylcyclopentadienyl) cations can be tuned by the proper selection of the arene system and by modification of the metal ion to make them more resistant to hydrolysis.
The ?-lactamase activity of two previously reported dinuclear cobalt(II) complexes is described. The two complexes, [Co2(CO2EtH2L1)(CH3COO)2](PF6) (CO2EtH3L1 = ethyl 4-hydroxy-3,5-bis{[(2-hydroxyethyl)(pyridin-2-ylmethyl)amino]methyl}benzoate) and [Co2(CO2EtL2)(CH3COO)2](PF6) (CO2EtHL2 = ethyl 4-hydroxy-3,5-bis{[(2-methoxyethyl)(pyridin-2-ylmethyl)amino]methyl}benzoate), differ in that the latter has methyl ether donors in contrast to potentially nucleophilic alkoxide donors in the former. They thus offer a direct comparison of potential ligand-centered nucleophiles. The complexes were treated with the antibiotic penicillin G and the commonly used lactamase substrate nitrocefin. On the basis of mass spectrometry, UV/Vis, and infrared spectroscopy measurements in solution, it was shown that only [Co2(CO2EtH2L1)(CH3COO)2](PF6) was capable of hydrolyzing both penicillin and nitrocefin, and that the hydrolysis-initiating nucleophile was an alkoxide donor. Analysis of kinetic data showed that nitrocefin binding occurs more rapidly {k1 = [(2.5?×?103)?±?(1.9?×?101)] M–1?min–1} than its subsequent hydrolysis {k2 = [(1.6?×?10–1)?±?(8.1?×?10–4)] min–1}. The pH dependence of nitrocefin hydrolysis by [Co2(CO2EtH2L1)(CH3COO)2]+ displays two pKa values (6.88?±?0.74; 8.45?±?0.68), the first of which is attributed to the deprotonation of a CoII alcohol, and the second of which is proposed to arise from CoII–OH2. For [Co2(CO2EtL2)(CH3COO)2]+, only one relevant pKa1 (8.47?±?0.14) is evident, assigned to a terminal water molecule. By using variable-temperature/variable-field magnetic circular dichroism (VTVH MCD), it was demonstrated that the sign of the magnetic exchange coupling parameter (J) for the parent dinuclear cobalt(II) complexes changes upon binding of the substrate. This work presents one of the few cobalt(II) ?-lactamase model complexes that is capable of facile hydrolysis of ?-lactam substrates, an outcome that provides a good benchmark to investigate the reaction mechanism(s) applicable to the enzyme systems.
Two dinuclear CoII complexes were tested for their ability to hydrolyze ?-lactam substrates. The [Co2(CO2EtH2L1)(CH3COO)2]+ complex is reactive towards nitrocefin and penicillin, whereas [Co2(CO2EtL2)(CH3COO)2]+ is unreactive. The difference between the two complexes is due to the presence of an alkoxide in the former.
The essential but also toxic gaseous signaling molecule nitric oxide is scavenged by the reduced vitamin B12 complex cob(II)alamin. The resulting complex, nitroxylcobalamin [NO–-Cbl(III)], is rapidly oxidized to nitrocobalamin (NO2Cbl) in the presence of oxygen; however, it is unlikely that nitrocobalamin is itself stable in biological systems. Kinetic studies on the reaction between NO2Cbl and the important intracellular antioxidant, glutathione (GSH), are reported. In this study, a reaction pathway is proposed in which the ?-axial ligand of NO2Cbl is first substituted by water to give aquacobalamin (H2OCbl+), which then reacts further with GSH to form glutathionylcobalamin (GSCbl). Independent measurements of the four associated rate constants k1, k–1, k2, and k–2 support the proposed mechanism. These findings provide insight into the fundamental mechanism of ligand substitution reactions of cob(III)alamins with inorganic ligands at the ?-axial site.
Kinetic studies on the reaction of nitrocobalamin (NO2Cbl) with glutathione show that glutathionylcobalamin (GSCbl) is formed via an aquacobalamin (H2OCbl+) intermediate. This reaction pathway is demonstrated by independently determining individual rate constants for each step.
A bis(?-diketone), 1,3-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenyl (BTP), which contains a trifluorinated alkyl group, has been exploited to obtain three series of visible-light sensitive dinuclear rare-earth complexes with the general formula [Ln2(BTP)3L2] [Ln = Nd, L = DME (1), bpy (2), and phen (3); Ln = Yb, L = DME (4), bpy (5), and phen (6); Ln = Er, L = DME (7); DME = ethylene glycol dimethyl ether, bpy = 2,2?-bipyridine, phen = 1,10-phenanthroline]. An X-ray crystallographic analysis revealed that complexes 1, 2, 4, 5, and 7 are triple-stranded helical dinuclear structures that are formed by three bis(bidentate) ligands with two lanthanide ions. The room-temperature near-IR luminescent properties of complexes 1–6 show that this bis(?-diketone) can effectively sensitize rare earths (Nd3+, Yb3+) and produce typical near-infrared luminescence upon excitation with visible light of the corresponding Nd3+ and Yb3+ ions. Additionally, two bidentate nitrogen ancillary ligands, 2,2-bipydine (bpy) and 1,10-phenanthroline (phen), have been applied to enhance the NIR luminescent properties.
A bis(?-diketone), 1,3-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenyl (BTP), has been designed and employed for the synthesis of three series of new BTP lanthanide complexes that featured promising NIR luminescence.
Hydrogenation of the neutral bis(allyl) complexes of the early lanthanides [Ln(Me3TACD)(?3-C3H5)2] [(Me3TACD)H = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, Me3[12]aneN4] with phenylsilane gave the tetranuclear octahydrido complexes [Ln(Me3TACD)(?-H)2]4 [Ln = Ce (1-Ce), Pr (2-Pr)] or the dinuclear allyl/hydrido complexes [Ln(Me3TACD)(?3-C3H5)(?-H)]2 [Ln = Nd (3-Nd), Sm (4-Sm)], which were isolated and characterized. The structures of 1-Ce and 2-Pr are constructed of a tetrahedral Ln4H8 core. Single-crystal X-ray diffraction analyses of 3-Nd and 4-Sm revealed a C2 symmetric planar Ln2H2 core. The experimental structures agreed with the results of DFT calculations, which predict that the nuclearity of the dihydrido complexes depend on the ionic radius of the metal. Compounds 1-Ce, 2-Pr, 3-Nd and 4-Sm were tested as catalysts in the copolymerization of cyclohexene oxide with CO2 to give highly carbonate-linked copolymers with moderate activities.
Tetranuclear [Ln(Me3TACD)(?-H)2]4 [Ln = Ce (1-Ce), Pr (2-Pr)] and dinuclear [Ln(Me3TACD)(?3-C3H5)(?-H)]2 [Ln = Nd (3-Nd), Sm (4-Sm)] have been obtained by treatment of the corresponding bis(allyl) Me3TACD complexes with phenylsilane and were tested as catalysts in the copolymerization of cyclohexene oxide with CO2.
In this microreview, we focus on our work on the development of group 5 imido and bis(imido) semihydrogenation catalysts in the context of previous stoichiometric studies on d0 metal–ligand multiple-bond activations of strong ? bonds and both stoichiometric and catalytic studies on H2 activation and hydrogenation by d2 group 5 complexes. These studies develop electronic structure models and mechanistic analyses necessary for the application of catalytic reactions involving 1,2-addition reactions of ?-bonded substrates across early transition metal–ligand multiple bonds. Extension of these studies to the second and third row group 5 imido complexes has led to the development of mechanistically distinct hydrogenation catalysts with product selectivities not readily obtainable with traditional late transition-metal catalysts that employ H2 as the reductant.
The selective, catalytic semihydrogenation of alkynes by group 5 imido and bis(imido) complexes is presented from synthetic and mechanistic perspectives in the context of previous stoichiometric studies on the d0 metal–ligand multiple-bond activation of strong ? bonds and both stoichiometric and catalytic studies on H2 activation and hydrogenation by d2 group 5 complexes.
The utility of the fac-[RuH3(PR3)3]– anion (R = Ph, C6H4-4-Me) for the preparation of new oligonuclear transition metal polyhydrides has been examined. The lithium salts [Li(thf)x{Ru(?-H)3(PPh3)3}] {1: R = Ph, x = 3; 1?: R = C6H4-4-Me (Tol), x = 2.5} react with [Cp*RuCl]4 (Cp* = C5Me5), ZnCl2, and CuCl(SMe2) to form new oligonuclear polyhydrido complexes. The compounds [Cp*Ru(?-H)3Ru(PR3)3] (2: R = Ph, 2?: R = Tol), [Zn{Ru(?-H)3(PPh3)3}2] (3), and [Cu2{Ru(?-H)3(PPh3)3}2] (4) were synthesized and characterized by multinuclear NMR and IR spectroscopy, and microanalysis. The molecular structures were determined by X-ray crystallography. Density functional theory calculations at the PBE-D3/def2-TZVP level support the proposed structures of the new polyhydride complexes. The impact of intramolecular London dispersion interactions on the optimized geometries is discussed.
Di-, tri-, and tetranuclear polyhydride complexes with a fac-[RuH3(PPh3)3]– anion are accessible by salt metathesis of [Li(thf)3{Ru(?-H)3(PPh3)3}] (1) with [Cp*RuCl]4, ZnCl2, and CuCl(SMe2). Complexes 2–4 have been characterized by X-ray crystallography and spectroscopic techniques. DFT calculations support the structural analyses and examine the influence of the London dispersion interactions.
N,N-Diethylcarbamates [NbE(O2CNEt2)3] (E = O, S) have been prepared in high yields by treating NbOCl3 or [NbSCl3(CH3CN)2] with CO2/NHEt2 in toluene at approximately –10 °C. The products were characterized by spectroscopic techniques, elemental analysis and X-ray diffractometry in the case of [NbO(O2CNEt2)3]. The molecular structure of the latter consists of a niobium centre coordinated to the oxido moiety and six O atoms belonging to bridging and bidentate carbamates, in a slightly distorted pentagonal-bipyramidal arrangement. The structures of both [NbE(O2CNEt2)3] compounds were reproduced by DFT calculations, which show substantial similarity despite the different nature of the chalcogen atoms.
N,N-Diethylcarbamates [NbE(O2CNEt2)3] (E = O, S) have been prepared from NbECl3 and fully characterized. The structures of both products have been optimized by DFT calculations.
This paper reports a new approach towards the construction of a multifunctional periodic mesoporous organosilica (PMO), which integrates a range of advantages, such as mesoporous structural order, selective nucleobase-recognition properties, stimuli-responsive site-specific delivery of anticancer agents to cancer tissues, and Cu2+ adsorption, into a single entity. First, the appropriate organic-functional-receptor precursor was synthesized by a chemical process and used to fabricate a multifunctional pyridine-containing PMO material (DMPy-PMO) by a hydrolysis and condensation route. The designed organic–inorganic hybrid mesoporous silica chemosensor showed an intrinsic selective recognition of nucleobase, specifically thymidine, through multipoint hydrogen-bonding interactions with suitably arrayed receptor sites loaded into the rigid silica framework. An in vitro cytotoxicity test showed that the designed chemosensor materials have good biocompatibility and, therefore, could be promising candidates for the delivery of a range of therapeutic agents. Confocal laser scanning microscopy (CLSM) confirmed that the material can be internalized effectively by cancer cells (MCF-7 cells). In addition, the DMPy-PMOs showed efficient Cu2+ ion removal capacity at pH 5.0 with significantly high levels of adsorption (0.95 mmol?g–1). These results suggest that the prepared multifunctional PMO hybrid has potential use as a smart material for a range of applications, such as biomolecule recognition, biomedical applications, and as an efficient adsorbent for the removal of metal ions.
A multifunctional mesoporous silica hybrid is presented, in which the receptor site plays a key role in nucleobase recognition, pH-induced delivery of anticancer agents, and as a metal binding site for Cu2+ ions. The pyridine-containing material selectively recognizes thymidine, is an effective potential drug-carrier system in cancer therapy, and is an efficient adsorbent for Cu2+ removal.
Dinuclear rhodium complexes have attracted considerable attention as a result of their chemical and biological reactivity. We report herein the synthesis and structural elucidation by combined spectroscopic methods of a new rhodium complex containing N-methyl-D-phenylalaninate (NMfO–) as a chiral ligand. It has been demonstrated that the structure of the chiral complex formed in water is independent of the ligand/metal molar ratio, the type of solvent, and reaction time, as shown by HPLC and ESI-MS analyses. The steric structure of the isolated and identified [Rh2(OAc)2(OfMN)2] complex was determined by chiroptical (VCD, ECD) and NMR spectroscopy supported by DFT calculations. By this combined analysis, our studies have shown that the complex formed has two chiral ligands chelated through the O and N atoms of their carboxylate and sec-amino groups, respectively, in the vicinity of the two bridging acetate ligands.
The steric structure and binding mode of the isolated new chiral dirhodium complex [Rh2(OAc)2(OfMN)2] have been determined by chiroptical (VCD, ECD) and NMR spectroscopy supported by DFT calculations.
Metalloligands L1 and L2 consisting of directional bis(terpyridine)ruthenium(II) units and bipyridine moieties were constructed by amide formation. From these metalloligands two Ru–Pt heterobimetallic complexes 1 and 2 were derived by a building-block method by means of platination with [PtCl2(dmso)2]. Both bimetallic complexes 1 and 2 feature metal-to-ligand charge transfer (MLCT) absorptions, and emission occurs at room temperature in fluid solution from 3MLCT(Ru) states in all cases. Energy transfer from platinum to ruthenium is observed in 2 but not in 1 (light harvesting). The one-electron-reduced species [1]– and [2]– were prepared by reduction of 1 and 2 with decamethylcobaltocene. EPR spectra and DFT calculations reveal that the spin density is localized at the tpy–CO/Ru (tpy = terpyridine) site in [1]–, whereas it is centered at bpy–CO/Pt (bpy = 2,2?-bipyridine) in [2]–. Efficient photoinduced electron transfer from triethanolamine to 1 and 2 is feasible by excitation at 500 nm [MLCT(Ru)].
Heterobimetallic complexes Pt–Ru (1) and Ru–Pt (2) were constructed from directional bis(terpyridine) ruthenium(II) and bipyridinedichloroplatinum(II) moieties. The photophysical properties of 1 and 2 as well as their responses to one-electron reduction (thermal and photochemical) were elucidated by EPR spectroscopy, DFT calculations, and Stern–Volmer plots.
The connection of flexible protodendritic wedges to the bis-tridentate rigid polyaromatic ligand L1 provides amphiphilic receptors L5 and L6; their reduced affinities for complexing trivalent lanthanides (Ln = La, Y, Lu) in organic solvent (by fifteen orders of magnitude!) prevent the formation of the expected dinuclear triple-stranded helicates [Ln2(Lk)3]6+. This limitation could be turned into an advantage because L1 or L6 can be treated with [Ln(hfac)3] (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione) to give neutral single-stranded [Ln2(Lk)(hfac)6] complexes with no trace of higher-order helicates. Whereas ligands L1 and L5 are not liquid crystals, L6 can be melted above room temperature (41 °C) to give a nematic mesophase, and its associated dinuclear helical complex [Y2(L6)(hfac)6] self-organises at the same temperature into a fluidic smectic mesophase.
The lipophilic dendritic ligand L6 selectively reacts with trivalent yttrium hexafluoroacetylacetonate (hfac) to give the liquid-crystalline single-stranded dinuclear helicate [Y2(L6)(hfac)6], which self-organises into an SmA mesophase.
A mixed-ligand 3D metal–organic framework, [Ni(1,2-cpd)(bpe)(H2O)]n (1) [1,2-cpd = cis-cyclopentane-1,2-dicarboxylate, bpe = 1,2-di(4-pyridyl)ethylene], has been constructed. Topological analysis revealed that the structure is a 3-c uninodal 2D + 2D ? 3D polycatenated net with the Schläfli symbol 63. The compound is catalytically active towards the epoxidation reaction in heterogeneous media. It catalyses almost all types of olefinic substrates with equal efficiency. After reaction it can be recovered quite easily and can be used for further reaction without any loss of activity for several cycles. Variable-temperature magnetic susceptibility measurement reveals the presence of a weak antiferromagnetic interaction in compound 1.
A mixed-ligand nickel–organic framework has been made that has a 3-c uninodal 2D + 2D ? 3D polycatenated net. It can catalyse almost all types of olefinic substrates with equal efficiency and be used for several cycles without loss of any catalytic activity.
CdV2O6 and Cd2V2O7 were successfully synthesized by a simple hydrothermal process. The effects of the hydrothermal temperature and pH on the phase transition between CdV2O6 and Cd2V2O7 were investigated in detail. That the Cd2V2O7 phase could transform into CdV2O6 was attributed to polymerization of vanadate in an acidic environment as the V/O ratio increased as the pH decreased. V2O74– was stable in a neutral or alkaline environment at an identical hydrothermal temperature, therefore, the Cd2V2O7 phase was obtained after hydrothermal treatment for 24 h. Because the degree of hydrolysis of NH4Cl increased with increasing temperature in the solution, the increased temperature accelerated the speed of the pH decrease. Therefore, the hydrothermal temperature played an important part in the phase transition between CdV2O6 and Cd2V2O7. CdV2O6 and Cd2V2O7 showed high photocatalytic activity for the degradation of methylene blue under visible-light irradiation.
CdV2O6 and Cd2V2O7 are controllably synthesized by a simple hydrothermal method. The influence of the reaction parameters (pH, hydrothermal temperature) on the phase transition between CdV2O6 and Cd2V2O7 and the relationship between the phases and photocatalytic activities are investigated.
Four azide–copper coordination polymers, [Cu2L1(N3)4]n, [Cu2L2(N3)4]n, [Cu2L3R(N3)4]n, and [Cu2L3S(N3)4]n, were synthesized by using pybox [pyridine-2,6-bis(oxazolines)] as coligands {L1: 2,6-bis(4,5-dihydrooxazol-2-yl)pyridine; L2: 2,6-bis(5,6-dihydro-4H-1,3-oxazin-2-yl)pyridine; L3R or 3S: 2,6-bis[(R or S)-4-benzyl-4,5-dihydrooxazol-2-yl]pyridine}. Compounds 1 and 2 possess similar 1D infinite azide–copper hexagonal tapes with three types of N3 bridges (two single end-on N3 bridges and one double end-on N3 bridge). Compounds 3R and 3S possess an azide–copper 2D honeycomb layer with two types of N3 bridges (a single end-to-end N3 bridge and a double end-on N3 bridge). The chirality of these enantiopure layered structures is controlled by the addition of the chiral pybox ligand in the synthesis, which is very rare for the reported azide–copper coordination polymers. The double end-on N3 bridge transfers mainly ferromagnetic exchange coupling interactions in these four compounds. Owing to the steric hindrance of the pybox ligands, the interchain and interlayer separations are broadened, which weakens the magnetic interactions between them. Thus, no long-range ferromagnetic ordering was observed above 1.8 K. A magnetostructural correlation was also discussed in detail.
A series of pybox ligands were used as effective coligands to construct four azide–copper low-dimensional coordination polymers. Two of these polymers possess similar 1D infinite azide–copper hexagonal tapes and the other two possess a very interesting enantiopure 2D honeycomb layer structure. Magnetic studies revealed the weak ferromagnetic characters of these complexes.
The useful optoelectronic properties of cationic iridium(III) complexes have been exploited in diverse applications, from visual displays to biological probes to analytical sensors. It is thus not surprising to note the increased recent efforts to document, understand, and ultimately control the photophysical and electrochemical properties of the archetypal cationic iridium(III) complex [(ppy)2Ir(bpy)]+, in which ppyH = 2-phenylpyridine and bpy = 2,2?-bipyridine, and decorated versions thereof. Of the ligand architectures explored, the greatest attention has been devoted to ligands that incorporate the common pyridine unit. In this Microreview, we survey the salient emission and electrochemical properties of cationic iridium(III) complexes of the form [(C?N)2Ir(L?X)]+, in which C?N is a cyclometalating ligand and L?X is a bidentate neutral ancillary ligand, with at least one heterocyclic ligand other than pyridine. We contrast their properties to that of [(ppy)2Ir(bpy)]+ and highlight recent exploits in materials applications.
This Microreview summarizes the optoelectronic properties of luminescent cationic iridium complexes bearing nontraditional ligand motifs with generalized structure [(C?N)2Ir(L?X)]+, in which C?N is a cyclometalating ligand and L?X is a bidentate neutral ancillary ligand, with the goal of elucidating structure–property trends. Their use in applications such as photosensitizers for solar fuels and as luminophores in light-emitting electrochemical cells is also discussed.
A new Ru2 azido complex, [Ru2(chp)4N3] (4, chp = 2-chloro-6-hydroxypyridinate), was investigated under photolytic conditions to study the chemical reactivity of the corresponding Ru2 nitride species, [Ru2(chp)4N] (6), towards intermolecular N atom transfer to triphenylphosphane (PPh3). Photolysis of a dichloromethane solution of 4 at ? > 350 nm leads to a characteristic color change from purple to magenta. Upon acidic workup, triphenylphosphanamine chloride ([H2NPPh3]Cl) is produced and [Ru2(chp)4Cl] (5), the precursor to 4, is regenerated. The first stoichiometric cycle for intermolecular N atom transfer from a Ru2 nitride is thus presented.
The new Ru2 azido complex [Ru2(chp)4N3] (chp = 2-chloro-6-hydroxypyridinate) reacts with PPh3 under photolytic conditions to form [H2NPPh3]+Cl– and [Ru2(chp)4Cl], from which the azide complex can be regenerated.
Addition of TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) to a toluene slurry of AlBr3 results in rapid formation of AlBr3(?1-TEMPO) (1), which can be isolated in 65?% yield. In contrast, addition of TEMPO to a hexanes solution of BBr3 results in formation of [TEMPO][BBr4] (2) and (TEMPO)2BBr (3), the products of TEMPO disproportionation. Complexes 1–3 have been fully characterized, including analysis by X-ray crystallography. The divergent reactivity is likely dictated by the Lewis acidity of the group 13 halide, and in the case of the stronger Lewis acid BBr3, coordination of TEMPO to the boron center generates an adduct that is capable of oxidizing free TEMPO.
The outcome of the reaction between TEMPO and MBr3 (M = B, Al) was found to depend on the Lewis acidity of the group 13 element. Addition of TEMPO to AlBr3 results in formation of the 1:1 adduct, AlBr3(?1-TEMPO). In contrast, addition of TEMPO to BBr3 results in TEMPO disproportionation and formation of [TEMPO][BBr4] and (TEMPO)2BBr.
A novel synthetic route based on [4+2] cycloaddition for dibromobenzobarrelene derivatives starting from in situ generated 3,5-dibromo-1,2-didehydrobenzene and mesitylene, 1,2,4,5-tetramethylbenzene, 1,2,3,5-tetramethylbenzene, pentamethylbenzene, 1,3-dimethoxybenzene, and 2,4,6-trimethylbromobenzene, respectively, was developed. Thus, six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework including chiral derivatives are reported. The benzobarrelene 6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene (1a) was functionalized at the annulated benzene ring to give three novel carboxylic acids and two novel phosphonic acid esters. Selected benzobarrelene complexes with RhICl were tested for their catalytic activity in the 1,4-addition of phenylboronic acid towards cyclohex-2-enone. Turnover frequencies up to 3405 h–1 were observed, which are among the highest reported so far for Rh–diene complexes in this type of C–C coupling reaction.
The synthesis by means of a [4+2] cycloaddition approach of six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework, including chiral derivatives, is reported as well as the functionalization of 6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene to give carboxylic acid and phosphonic acid ester derivatives.
Although phosphonous acid ligands have recently become of interest for use in transition metal complex catalysts for organic reactions such as alkene hydroformylations, the factors that affect the steric and electronic properties of these ligands have not been studied in detail. To gain insight into the electronic and steric properties of phosphonous acid ligands, we have prepared tungsten(0) pentacarbonyl complexes with chlorophosphite ligands derived from either 2,2?-biphenol or (±)-1,1?-bi-2-naphthol and have then hydrolyzed the coordinated ligands to generate tungsten(0) pentacarbonyl complexes with the corresponding phosphonous acid ligands. NMR measurements of the W–P coupling constants demonstrate that changing the biaryl groups from biphenyl to binaphthyl does not affect the electron-donor ability of the ligand, whereas changing the third substituent from chloro to oxo has a significant effect. Estimation of cone angles of the ligands from X-ray crystallographic data have shown that neither changing the biaryl group nor changing the third substituent have a significant effect on their cone angles. Further, these studies have identified important intra- and intermolecular interactions that favor certain ligand conformations. The data could be useful for the development of catalytic structure–activity relationships that could be used in the rational design of catalysts.
Steric and electronic properties of chlorophosphite ligands derived from 2,2?-biphenol or (±)-1,1?-bi-2-naphthol and their corresponding phosphonous acid ligands in tungsten(0) pentacarbonyl have been studied by using multinuclear NMR spectroscopy and X-ray crystallography. The identity of the biaryl group does not affect either the steric or the electronic properties of the ligands.
[Fe]-hydrogenase, one of three types of hydrogenases, activates molecular hydrogen. Here, using DFT computations, we examine the electronic elements governing the binding of small ligands to a recently synthesized [Fe]-hydrogenase biomimic. Computed reaction free energies indicate that anionic species, such as CN– and H–, and ? acceptors, such as CO, bind favourably with the Fe centre. Ligands such as H2O, CH3CN, and H2, however, do not bind iron. Protonation of an adjacent thiolate ligand on the mimic significantly increases the energies of ligand binding. Additional computational analysis reveals that the degree of electron donation from the ligand to the mimic correlates strongly with overall binding ability. The results give insights into the electronic elements of iron–small-molecule interaction in these model complexes.
The electronic effects that dictate the binding of small molecules to a [Fe]-hydrogenase mimic are examined by DFT computations. Analysis reveals that a ligand's ability to donate electron density to the Fe centre determines the overall reaction free energy.
The first two lanthanum selenide chlorides, LaSeCl and La3Se4Cl, both crystallize orthorhombically in space group Pnma (no. 62). They emerged from reactions of LaCl3 with lanthanum and selenium in appropriate molar ratios at 800–900 °C. Single crystals of the yellow LaSeCl adopt the cotunnite-type structure of PbCl2 with a = 760.63(5), b = 433.52(3) and c = 910.07(6) pm (Z = 4). The tricapped trigonal prisms [LaSe5Cl4]11– share their triangular faces to form chains that run parallel to the [010] direction and are condensed through caps and common edges to give a complete crystal structure in accord with ?3{LaSe5/5Cl4/4}. Dark-red La3Se4Cl exhibits the U3S5-type structure with a = 1271.98(5), b = 855.84(3) and c = 795.05(2) pm (Z = 4). The chloride anions are located at the Wyckoff position 8d together with selenium showing site occupation factors of 0.5 for both anion types. Bicapped trigonal prisms [LaSe7Cl]12– with (La2)3+ are connected through common faces and corners to form a three-dimensional framework suited to the embedding of chains of fused tricapped trigonal prisms [LaSe5+1Cl2]11– with (La1)3+ running parallel to [010]. The absorption edge energy of approximately 1.75 eV indicates a wide band-gap semiconductor that is stable towards air, water and some aqueous bases at different concentrations.
The crystal structures of the first lanthanum selenide chlorides, LaSeCl and La3Se4Cl, are described in terms of condensed bi- and tricapped trigonal prisms [LaSenClm]11/12– (n = 5, 5+1, 7; m = 1, 2, 4). A phase-pure sample of La3Se4Cl displays an optical band gap of 1.75 eV. Both show high stability towards air, water and inorganic bases, but decompose upon contact with acids.
Novel phosphors, Ca2YF4PO4:Eu2+,Mn2+, have been prepared by high-temperature solid-state reactions. XRD and XPS techniques were used to investigate the purity and composition of the as-prepared samples. The Ca2YF4PO4:Eu2+,Mn2+ phosphors exhibit broad excitation spectra ranging from 275–420 nm and the emission spectra show a broad blue emission band centered at 455 nm and a yellow emission band centered at 570 nm, which originate from the Eu2+ and Mn2+ ions, respectively. Energy transfer from the Eu2+ to Mn2+ ions in the Ca2YF4PO4 host matrix was observed and studied by luminescence spectrosccopy as well as the lifetime of the Eu2+ ions. The emission color of the Ca2YF4PO4:Eu2+,Mn2+ samples can be adjusted from blue to yellow under excitation by UV radiation of 375 nm by adjusting the Eu2+ and Mn2+ concentrations, and white-light emission with chromaticity coordinates (0.327, 0.312) was obtained with the Ca2YF4PO4:0.015Eu2+,0.015Mn2+ sample. In addition, the temperature-dependent photoluminescence of the as-prepared phosphors has been investigated in detail. The results revealed that the Ca2YF4PO4 host has good thermal stability. The stable structure of the host and tunable luminescence suggest that Ca2YF4PO4:Eu2+,Mn2+ could be regarded as a good candidate for UV LED-based white-light emitting diodes.
The tunable luminescence and energy-transfer properties of Ca2YF4PO4:Eu2+,Mn2+ phosphors with potential application in LEDs have been investigated.
1,10-Diaza-18-crown-6 and 4,4?-trimethylenedipiperidine were transformed into bis-dithiocarbamate ligands, which were then reacted in situ with different di- and triorganotin(IV) chlorides to generate dinuclear monomeric or macrocyclic products. The identity of the compounds was established by elemental analysis, multinuclear NMR spectroscopy (1H, 13C, and 119Sn), IR spectroscopy, mass spectrometry, and for representative examples additionally by single-crystal X-ray diffraction analysis. In combination with DFT calculations, the structural characterization showed that diaryltin and dialkyltin fragments give macrocycles of different conformation owing to changes in the coordination stereochemistry (cis vs. trans isomers). The macrocycle cavities are suitable for the inclusion of guest molecules. At the supramolecular level, the Sn complex molecules are linked through intermolecular C–H···S and C–H···Cl interactions in the solid state.
Dinuclear monomeric and macrocyclic complexes derived from diorganotin dithiocarbamates are prepared by using ligands with azacrown and dipiperidine spacers. The macrocyclic structures have different conformations depending on the R2Sn group, which also changes the size of the cavity suitable for guest inclusion. The structures show supramolecular arrays through C–H···S and C–H···Cl interactions.
9-Hydroxy-2-methyl-phenalenone (MHPO) was synthesized and modified with 3-(triethoxysilyl)propyl isocyanate (TEPIC) through a hydrogen atom addition reaction to achieve a new chemical linkage (named as MHPOSi). SBA-15 mesoporous silica organically functionalized with MHPOSi was synthesized. The MHPOSi was linked to tetraethoxysilane (TEOS) through a condensation process in the presence of Pluronic P123 surfactant as a template. New Ln3+ (Eu3+, Nd3+, Yb3+) organic–inorganic mesoporous hybrid materials were prepared, in which the Ln3+ complexes are covalently attached to SBA-15 and have 1,10-phenanthroline (phen) as a second ligand. The resultant mesoporous hybrids were characterized by FTIR spectroscopy, small-angle X-ray diffraction, N2 adsorption–desorption measurements, thermal analysis, and UV/Vis spectroscopy. They all have high surface areas, uniform mesostructures, and good crystallinity. The photophysical properties of the functionalized mesoporous SBA-15 networks are discussed in detail and they still present excitation capability in the visible region despite the modification of the organic silane. Subsequently, they exhibit characteristic visible (Eu3+) and near-infrared (NIR) luminescence (Nd+ and Yb3+).
Ln3+ (Eu3+, Nd3+, Yb3+) organic–inorganic mesoporous hybrid materials are prepared. The hybrids contain lanthanide complexes covalently grafted to 2-methyl-9-hydroxyphenalenone (MHPO) functionalized ordered mesoporous SBA-15 and with 1,10-phenanthroline as a second ligand. The materials exhibit the characteristic visible (Eu3+) and near-infrared (NIR) luminescence (Nd+ and Yb3+) of lanthanides.
The reaction of H2C(PCl2)2 with four equivalents of iPrMgCl produces H2C(PiPr2)2, which was treated with tellurium in boiling toluene, or selenium in toluene at room temperature, to give the monochalcogenides EPiPr2CH2PiPr2 (E = Te, 4a; E = Se, 4b) in high yields. X-ray structural determinations show that 4a and 4b exist as the CH2 tautomers in the solid state with E–P–C–P dihedral angles of 56.1(2)° and 56.7(1)°, respectively. DFT calculations were carried out for the isolectronic series EPR2CH2PR2 and EPR2NHPR2 (E = Se, Te; R = Me, iPr, tBu, Ph) and for their non-chalcogenated precursors in order to elucidate the factors that determine the preference for PH tautomers in some PNP-bridged systems. Compounds 4a and 4b were also characterized by multinuclear (1H, 13C, 31P, 77Se, 125Te) NMR spectroscopy. In solution, 4a exhibits fluxional behavior, which has been investigated by variable-temperature and variable-concentration multinuclear NMR spectroscopy. The observed behavior is consistent with an intermolecular tellurium transfer with an activation energy of 21.9?±?3.2 kJ?mol–1; consideration of selenium exchange in 4b indicates a much higher energetic barrier. DFT calculations provide insights into the pathway for the chalcogen exchange process in 4a (?E = 20.4 kJ?mol–1). The outcome of reactions of 4a with selenium and nBuLi reflects the lability of the P-Te functionality.
The monochalcogenides EPiPr2CH2PiPr2 (E = Se, Te) exist as CH2 tautomers in the solid state; the contrast in this finding with that of the preferential formation of PH tautomers by PNP-bridged analogues is addressed through DFT calculations. In solution, the PCP-bridged tellurium derivative undergoes rapid intermolecular tellurium exchange with an activation energy of 21.9?±?3.2 kJ?mol–1.
To date, only a few nanosystems have been investigated as T1 MRI-CT dual contrast agents. The T1 MRI-CT dual functionality of a material depends on its longitudinal water-proton relaxivity (r1) and X-ray absorption strength. We explored Gd(IO3)3·2H2O nanomaterial because Gd is the most powerful element for T1 MRI contrast agents, and both Gd and I absorb X-ray radiation; Gd absorbs X-ray radiation ca. 2.5 times more strongly than I. D-Glucuronic acid coated Gd(IO3)3·2H2O nanomaterial showed a very large r1 of 52.3 s–1?mM–1 (r2/r1 = 1.21), which could be ascribed to hydrated water molecules in the lattice. Its X-ray absorption intensity was also stronger than those of commercial molecular iodine CT contrast agents. This result clearly suggests that D-glucuronic acid coated Gd(IO3)3·2H2O nanomaterial is a potential T1 MRI-CT dual contrast agent.
D-Glucuronic acid coated Gd(IO3)3·2H2O nanomaterial is synthesized in one-pot and its T1 MRI-CT dual imaging properties are investigated. It has a very large r1 and strong X-ray absorption, which are prerequisites for high-performance T1 MRI-CT dual contrast agents.
The incorporation of europium polyoxometalates into silica nanoparticles can lead to a biocompatible nanomaterial with luminescent properties suitable for applications in biosensors, biological probes, and imaging. Keggin-type europium polyoxometalates Eu(PW11)x (x = 1 and 2) with different europium coordination environments were prepared by using simple methodologies and no expensive reactants. These luminescent compounds were then encapsulated into silica nanoparticles for the first time through the water-in-oil microemulsion methodology with a nonionic surfactant. The europium polyoxometalates and the nanoparticles were characterized by using several techniques [FTIR, FT-Raman, 31P magic angle spinning (MAS) NMR, and TEM/energy-dispersive X-ray spectroscopy (TEM-EDS), AFM, dynamic light scattering (DLS), and inductively coupled plasma MS (ICP-MS) analysis]. The stability of the material and the integrity of the europium compounds incorporated were also examined. Furthermore, the photoluminescence properties of the Eu(PW11)x@SiO2 nanomaterials were evaluated and compared with those of the free europium polyoxometalates. The silica surface of the most stable nanoparticles was successfully functionalized with appropriate organosilanes to enable the covalent binding of oligonucleotides.
Europium polyoxometalates with distinct europium coordination are encapsulated in silica nanoparticles by a microemulsion methodology. Their surface is further functionalized with appropriate organic groups to originate biocompatible nanomaterials with suitable photoluminescent properties.
Nanocrystalline Li[Li0.2Mn0.54Ni0.13Co0.13]O2 was prepared by a layered-template method and was tested as a high-capacity and high-power cathode for Li-ion batteries. Structural characterization demonstrates that the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 nanoparticles have a high crystallinity with a monoclinic (C/2m) structure. This material exhibits an initial discharge capacity of 277.4 mAh?g–1 and a high coulombic efficiency of 87.3?%, with a very small capacity fade of 0.046?% per cycle over 100 cycles. Such excellent electrochemical performance is likely to result from its monoclinic structure that enables a stable solid solution structure and reversible structural changes during cycling. Therefore, monoclinic Li[Li0.2Mn0.54Ni0.13Co0.13]O2 may meet the high-capacity and high-rate requirements for an alternative cathode for a new generation of Li-ion batteries.
A layered-template method was used to synthesis the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 nanoparticles with a monoclinic structure. Due to the presence of the monoclinic structure, the cycling stability and rate capability of the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 electrode are excellent.
The treatment of [Ru(CO)2Cl2]x with 4,4?,4?-tri-tert-butyl-2,2?:6?,6?-terpyridyl (tbtpy) in tetrahydrofuran at reflux afforded trans-[Ru(tbtpy)Cl2(CO)] (1). The alkylation of complex 1 with excess Me3SiCH2MgCl afforded a mixture of trans-[Ru(tbtpy)(CH2SiMe3)2(CO)] (2) and trans-[Ru(tbtpy)(CH2SiMe3)Cl(CO)] (3), whereas complex 3 could be obtained in good yield by the alkylation of complex 1 with 1 equiv. of Me3SiCH2MgCl. On the other hand, the alkylation of 1 with MeLi and PhCH2MgBr afforded the monoalkyl complexes [Ru(tbtpy)(Me)Cl(CO)] (4) and [Ru(tbtpy)(CH2Ph)Cl0.5Br0.5(CO)] (5), respectively. The crystal structure of complex 5 was determined. Complex 2 and the previously prepared mer-[Ru(dtbpy)(CH2SiMe3)3(NO)] (dtbpy = 4,4?-di-tert-butyl-2,2?-bipyridyl) were immobilized on SBA-15 by treating the Ru complexes with SBA-15 in benzene at room temperature. 1H NMR spectroscopy indicated that the reaction of complex 2 and [Ru(dtbpy)(CH2SiMe3)3(NO)] with SBA-15 in C6D6 resulted in the formation of approximately 1 equiv. of SiMe4, which suggests the grafted species are possibly (?SiO)Ru(tbtpy)(CH2SiMe3)(CO) and (?SiO)Ru(dtbpy)(CH2SiMe3)2(NO), respectively. The Ru-grafted SBA-15 materials were characterized by IR, reflectance UV/Vis, and X-ray photoelectron spectroscopy as well as transmission electronic microscopy, and their catalytic performance in the oxidation of benzyl alcohol with tert-butyl hydroperoxide was examined.
The alkylation of [Ru(tbtpy)(CO)Cl2] (tbtpy = 4,4?,4?-tri-tert-butyl-2,2?:6?,6?-terpyridyl) with Me3SiCH2MgCl afforded a mixture of trans-[Ru(tbtpy)(CH2SiMe3)2(CO)] and trans-[Ru(tbtpy)(CH2SiMe3)Cl(CO)]. trans-[Ru(tbtpy)(CH2SiMe3)2(CO)] and mer-[Ru(dtbpy)(CH2SiMe3)3(NO)] were immobilized on SBA-15 by elimination of SiMe4 and the grafted species showed catalytic behavior.
Reactivity studies of aluminoxane hydroxide and hydrogensulfide [{MeLAl(EH)}2(?-O)] {MeL = CH[CMe(NAr)]2– (Ar = 2,4,6-Me3C6H2); E = O (1), S (2)} with Group 4 amides led to the molecular heterobimetallic aluminoxanes [(MeLAlO)2(?-O){M(NR2)2}] [M = Ti, R = Me (3); M = Zr, R = Me (4), Et (5); M = Hf, R = Me (6), Et (7)] and aluminoxane sulfides [(MeLAlS)2(?-O){M(NR2)2}] [M = Ti, R = Me (8), Et (9); M = Zr, R = Me (10), Et (11); M = Hf, R = Me (12), Et (13)], respectively. The structural analyses of these compounds reveal six-membered inorganic cores that exhibit Al–E–M (E = O, S; M = Ti, Zr, Hf) moieties. Compounds 10–13 exhibit strong O···M (M = Zr, Hf) transannular bonding, whereas 8 and 9 exhibit relatively short Ti–S bond lengths. DFT calculations performed on 8–13 at the B3LYP/LANL2DZ level of theory indicate that the titanium atoms in 8 and 9, despite having the lowest transannular bond index, have the highest total Wiberg bond indexes. This can be rationalized in terms of the high Ti–S bond indexes, which indicate an important degree of electron density delocalized from the sulfur atoms to the titanium atom.
A series of Group 4 heterobimetallic aluminoxanes and aluminoxane sulfides have been prepared. The aluminoxane sulfides exhibit unprecedented Al–S–M (M = Zr, Hf) moieties. The structural and electronic features of these compounds were investigated by DFT calculations.
The multinuclear silicon complexes [{H2ClSi(?-pz*)2}2SiH2] (1) and [Cl2Si(?-pzRR)2SiCl2] (2, R = Me; 3, R = Ph) were formed by the reaction of dichlorosilane (for 1) or hexachlorodisilane with 1-trimethylsilyl-3,5-dimethylpyrazole (for 1 and 2) and the 3,5-diphenyl analogue (for 3). The reaction of trichlorosilane with 3,5-dimethylpyrazole (Hpz*) in MeCN resulted in the formation of two MeCN insertion products of 2 (4, 5). From different samples of synthesis products of this work a preferred hydrolysis product was obtained: [{(?-pz*)2SiH}3–?3-O]+Cl– (6). The structural and electronic features of the compounds synthesised in this work were analysed with single-crystal X-ray diffraction and 29Si cross-polarisation (CP)/magic-angle spinning (MAS) NMR spectroscopy combined with quantum chemical computations to investigate their 29Si chemical-shift anisotropy principal tensor components.
The reaction of trichlorosilane with 3,5-dimethylpyrazole (Hpz*) in acetonitrile afforded dinuclear silicon compounds. Their outstanding feature is the formal insertion of one or two molecules of MeCN into the former N–Si bond of a Sipz* moiety. These compounds were examined with single-crystal X-ray diffraction, 29Si cross-polarisation (CP)/magic-angle spinning (MAS) NMR spectroscopy and quantum chemical calculations.
The guanidine proligands {2-[4-(tert-butyl)phenyl]-1,3-diisopropylguanidine} (1), [2-(4-methoxyphenyl)-1,3-diisopropylguanidine] (2) and [2-(4-bromophenyl)-1,3-diisopropylguanidine] (3) have been prepared by guanylation of anilines with diisopropylcarbodiimide, using [MgBz2(thf)2] as the catalyst at room temperature. These proligands react with the complex {[Nb(CH2SiMe3)3(CH3CN)]2(?-1,4-NC6H4N)} (4) to afford new guanidinate-supported dialkyl niobium dinuclear complexes [{Nb(CH2SiMe3)2[(4-tBuC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (5), [{Nb(CH2SiMe3)2[(4-MeOC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (6) and [{Nb(CH2SiMe3)2[(4-BrC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (7). Treatment of compounds 5–7 with 2 equiv. of 2,6-dimethylphenyl isocyanide gave the imido bis(iminoacyl) compounds [{Nb(Me3SiCH2C=Nxylyl)2[(4-tBuC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (8), [{Nb(Me3SiCH2C=Nxylyl)2[(4-MeOC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (9) and [{Nb(Me3SiCH2C=Nxylyl)2[(4-BrC6H4)N=C(NiPr)(NHiPr)]}2(?-1,4-NC6H4N)] (10). The molecular structures of compound 2 and complex 9 have been determined.
Dinuclear alkyl diimidoniobium complexes reacted with catalytically obtained guanidines to yield guanidinate complexes. Double bis(iminoacyl) derivatives were obtained by a migratory insertion reaction of 2,6-dimethylphenyl isocyanide.
A (?-diketiminato)nickel(II) hydrazido(1–) complex [LtBuNi(?2-N2H3)], {1, LtBu = [HC(CtBuNC6H3{iPr}2)2]–} has been obtained by treatment of [LtBuNiBr] with hydrazine. In a reaction of 1 with two equivalents of the azo compound diisopropyl azodicarboxylic ester (adc–OiPr) the Ni(N2H3) entity acts as both a hydrogenating and a reducing agent: diisopropyl hydrazidodicarboxylate (hdc–OiPr) is formed, and more adc–OiPr is reduced by two electrons. The resulting (adc–OiPr)2– is found as a ligand in the ultimate nickel product complex, the trinuclear nickel(II) compound [LtBuNi(?-adc–OiPr)Ni(?-adc–OiPr)NiLtBu] (2), in which two LtBuNi+ units are linked by a [NiII(adc–OiPr)2]2– moiety. The hypothesis that LtBuNiI species are acting as intermediates was supported by the independent finding that 2 can also be obtained by reaction of [LtBuNi(OEt2)] with adc–OiPr.
A (?-diketiminato)nickel hydrazido(1–) complex has been synthesized that acts as a four-electron reductant towards a diazene: The corresponding hydrazine is formed, as well as a novel trinuclear complex with bridging hydrazido(2–) ligands, which can also be obtained through activation of the diazene at nickel(I) precursors.
Energy storage and conversion schemes based on environmentally benign chemical fuels will require the discovery of faster, cheaper, and more robust catalysts for the oxygen-evolution reaction (OER). Although the incorporation of pendant bases into molecular catalysts for hydrogen production and utilization has led to enhanced turnover frequencies, the analogous incorporation of pendant bases into molecular catalysts for water oxidation has received little attention. Herein, the syntheses, structures, and catalytic activities of new iron complexes with pendant bases are reported. Of these new complexes, [Fe(L1)]2+ {L1 = N,N?-dimethyl-N,N?-bis(pyridazin-3-ylmethyl)ethane-1,2-diamine} is the most active catalyst. Initial turnover frequencies of 141 and 24 h–1 were measured by using ceric ammonium nitrate at pH 0.7 and sodium periodate at pH 4.7, respectively. These results suggest that the incorporation of pendant bases into molecular catalysts for water oxidation might be an effective strategy that can be considered in the development of new catalysts for the OER, but will require the careful balance of many factors.
The structural, electrochemical, and catalytic properties of a family of iron-containing homogeneous water oxidation catalysts with pendant heteroatoms are studied. Slightly faster O2 evolution relative to a parent compound is observed when the solvent pH is matched to the pKa of the pendant nitrogen base, which might be attributable to interactions with substrate water.
Reaction of [2-{(CH2O)2CH}C6H4]Li with SnCl4 in a 4:1 molar ratio afforded [2-{(CH2O)2CH}C6H4]4Sn (1), which was deprotected to give [2-(O=CH)C6H4]4Sn (2). Homoleptic [2-(RN=CH)C6H4]4Sn [R = Me2NCH2CH2 (3), 2,4,6-Me3C6H2 (4), PhCH2 (5)] were obtained by condensation of 2 with the corresponding amine either in solution or by using a green, solvent-free procedure for (imino)arylmetal species. All compounds were characterised by multinuclear NMR spectroscopy and mass spectrometry, and their molecular structures were determined by single-crystal X-ray diffraction. In all cases, the C4Sn core is distorted tetrahedral as a result of the combined effects of the intramolecular coordination of the heteroatoms from the organic ligands and the steric impediments imposed by the ligands. The overall coordination around tin was found to be different, that is, coordination numbers from six for 1 and 4, to seven for 3 and 5 and eight for 2. Compound 2 is the first example of a mononuclear tetraorganotin(IV) compound that contains an octacoordinated metal centre with a double helicate topology in the solid state. Multinuclear NMR spectroscopy studies in solutions of CDCl3 are consistent with equivalent organic groups attached to a tetracoordinate tin atom.
Homoleptic tetraorganotin(IV) compounds with hexa-, hepta- and octacoordinated metal centres were prepared. A solvent- and catalyst-free green synthetic method was used to obtain three (imino)aryltin derivatives. A mononuclear, octacoordinated, double helical tetraorganotin(IV) compound is reported.
Direct metalation reactions of diphenylamine and carbazole by using an amido-bridged dinuclear Al2 complex proceeded across two aluminum atoms while maintaining the dinuclear structure. In contrast, an aryloxido-bridged dinuclear aluminium complex was inert to the C–H metalation reaction. Such different reactivity of the alkylaluminum complexes with an [Al2O2] or [Al2N2] core was attributed to the space available for the secondary amine substrates to approach the Al–Me moiety: the flexibility provided by the bridging amido ligand forms an Al2N2 core with both a planar and butterfly shape, which creates enough space for the Al–Me moiety to activate the amines.
Direct metalation reactions of diphenylamine and carbazole were achieved by using amido-bridged dinuclear Al2 complexes. By comparing the inertness of the aryloxido-bridged dinuclear aluminum complexes for the C–H metalation reaction, we found that the Al2N2 core created enough space for the secondary amine substrates to approach the Al–alkyl moiety due to the flexibility of the bridging amido ligand, which allows the Al2N2 core to form both a planar and butterfly shape.
Over the last 15 years or so, it has been shown that low-valent, electron-rich uranium(III) complexes exhibit a wide variety of reactivity towards small molecules. As a result, the field of uranium-mediated small-molecule activation chemistry has undergone significant development in recent years. The classical organometallic reactivity patterns of oxidative addition and reductive elimination that dominate the chemistry of transition-metal complexes are much less common for uranium. Owing to the invocation of the 5f orbitals for bonding and the highly polarising nature of the actinide centre, the prevalent reactivity observed for non-aqueous uranium compounds is that of migratory insertion, ?-bond metathesis and redox activity, and this can account for the often unexpected chemistry encountered with these species. This microreview focuses on the activation chemistry of trivalent uranium complexes towards the important small molecules dinitrogen (N2), nitric oxide (NO), azide (N3–), carbon monoxide (CO) and carbon dioxide (CO2).
Low-valent, electron-rich UIII complexes have the ability to access a wide range of novel reactivity patterns with small molecules. This microreview focuses on the activation chemistry of trivalent uranium complexes towards the industrially relevant small molecules N2, NO, N3–, CO and CO2, outlining the often unexpected chemistry observed for these reactive UIII centres.
Borylation of hafno- and zirconocene complexes [(?5-C5H2-1,2,4-Me3)2M]2(?2,?2,?2-N2), containing strongly activated dinitrogen ligands, with pinacolborane (HBPin) resulted in N–B and M–H bond formation. Treatment of the borylated products with carbon monoxide triggered N–N bond scission with concomitant N–C bond formation to produce ?-borylimido and ?-formamidido fragments. Conversely, addition of tBuNC resulted in insertion of the isocyanide ligand into the M–H bonds and furnished the corresponding ?2-iminoacylhafnocene complexes.
Use of pinacolborane to borylate a hafnocene complex with a highly activated, side-on bound dinitrogen ligand resulted in N–B and M–H bond formation. Carbonylation of the functionalized hafnocene product triggers N–N cleavage to borylimido and formamidido ligands, thereby expanding the scope of CO-induced N2 bond cleavage.
Aryl amido iridium complexes supported by a tridentate phosphanyl–carbene–phosphanyl pincer ligand [(PC?sp?2P)Ir–N(H)Ar, Ar = C6H5, 1a; Ar = 2,6-iPr2C6H3, 1b] react with acetonitrile to afford the dimeric complex 2, in which two (PC?sp?2P)Ir fragments are bridged by a diiminato ligand derived from two molecules of CH3CN. Metrical parameters obtained from X-ray structural determination of 2 confirm that the bridging ligand is a diiminato species rather than an enediamido moiety, which indicates that the reductive coupling is mediated by one electron per iridium center. Experiments suggest that the reaction proceeds by heterolytic cleavage of the Ir–N(H)Ar bond followed by one-electron reduction of the resulting IrI–NCCH3 cation by the amido anion. The resulting anilino radical rapidly abstracts a hydrogen atom from the solvent. The reductive coupling of acetonitrile at a late transition metal center is unusual and in this instance occurs as a result of the highly ?-donating, electron-rich nature of the PC?sp?2P ligand.
Electron-rich IrI aryl amido complexes undergo heterolytic bond cleavage and one-electron reduction to effect coupling of a coordinated acetonitrile ligand. The dimeric product features a bridging diiminato ligand. The ability to mediate this coupling with a late transition metal attests to the highly donating nature of the PC?sp?2P pincer ligand environment.
A half-sandwich, coordinatively unsaturated N-heterocyclic carbene complex of iron with a metallacycle was found to cleave the Si–H bonds of hydrosilanes to give 16-electron iron–silyl complexes. The reactions of silyl complexes with H2 led to the formation of dihydride complexes, in which hydride ligands weakly interact with the silicon atom. The molecular structures of these new complexes have been determined by means of X-ray crystallography.
A half-sandwich, 16-electron iron complex with a cyclometalated N-heterocyclic carbene ligand was found to activate the Si–H bonds of hydrosilanes, thus giving rise to coordinatively unsaturated iron–silyl complexes. The silyl complexes interact with H2 to form 18-electron dihydride complexes.
Benzimidazolium salts N,N?-disubstituted with 9-alkylfluorenyl groups (3a–e, alkyl = methyl, ethyl, propyl, butyl, benzyl) have been synthesised in high yields in three steps from o-phenylenediamine. This amine was treated with fluorenone in the presence of TiCl4 and tetramethylethylenediamine (TMEDA) to form N,N?-bis(9H-fluoren-9-ylidene)benzene-1,2-diamine (1) in 91?% yield. Diamines 2a–e were then obtained in yields superior or equal to 77?% by reacting diimine 1 with the appropriate organolithium reagent. In the final step, diamines 2a–e were treated with ethylorthoformate under acidic conditions to afford benzimidazolium salts 3a–e. These were readily converted into the PEPPSI palladium complexes 4a–e (PEPPSI = pyridine-enhanced precatalyst preparation stabilisation and initiation). NMR and X-ray diffraction studies revealed that the flat fluorenylidene moiety orientates the alkyl groups towards the metal centre and because of its restricted rotational freedom makes the ligand bulkiness time independent. Thus, the metal centre is permanently confined between the two alkyl groups, and thereby forms a monoligating clamp with the carbenic centre. The CH2 groups close to the palladium ion give rise to anagostic C–H···Pd interactions. Catalytic tests revealed that the palladium complexes 4a–e are highly efficient in Suzuki–Miyaura cross-coupling reactions; their activity is equal or superior to the best PEPPSI catalysts reported to date.
N-Heterocyclic carbene ligands act as clamps with Pd centres to form highly active Suzuki–Miyaura cross-coupling catalysts. The remarkable performance displayed by these ligands relies on the presence of expanded 9-alkylfluorenyl substituents with a restricted rotational freedom, which results in a permanent, meridional confinement of the metal centre.
The phosphanylbipyridine ligands 6-(diphenylphosphanyl)-4,4?-dimethyl-2,2?-bipyridine (PPh2-Me2-bipy, a), 4,4?-di-tert-butyl-6-(diphenylphosphanyl)-2,2?-bipyridine (PPh2-tBu2-bipy, b), and 6-(diisopropylphosphanyl)-2,2?-bipyridine (PiPr2bipy, c) and the corresponding dinuclear copper complexes [Cu2(?-PPh2-Me2-bipy)2(NCCH3)2](PF6)2 (1), [Cu2(?-PPh2-tBu2-bipy)2(NCCH3)2](PF6)2 (2), [Cu2(?-PiPr2bipy)2(?-NCCH3)](PF6)2 (3), and [Cu2(?-PiPr2bipy)2{?-CNCH(CH3)2}](PF6)2 (4) were synthesized. The X-ray structures of 1–4 show that the complexes are dinuclear with the bidentate bipyridine coordinating to one copper atom and the phosphane moiety coordinating the other copper center. Complexes 3 and 4 possess short Cu–Cu distances with bridging acetonitrile and isocyanide ligands. The cyclic voltammograms of 1–4 were examined under N2 and CO2. Under N2, 1–3 show four quasi-reversible 1e– reductions, and under CO2, they show current enhancement at the second reduction. In comparison, complex 4 shows four irreversible reductions under N2 and no current enhancement under CO2.
Three phosphanylbipyridine ligands that react with CuI to form dimeric complexes have been synthesized and structurally characterized. The Cu–Cu distance can be controlled by ligand substitution, and electrochemical studies of the dimers suggest that four sequential 1e– reductions of the bipyridine ligands occur. Catalytic behavior is observed under CO2.
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