Coordination of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzimMe)]2MCl2 complexes (M = Zn, Cd, Hg).

The reactions of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzimMe), towards the zinc and cadmium halides, MX2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzimMe)]2MX2, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzimMe)]2ZnX2 and [H(sebenzimMe)]2CdX2 (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzimMe)]2ZnI2 and [H(sebenzimMe)]2CdI2, exhibit only one intramolecular N-H•••I interaction. Comparison of the M-Se and M-Cl bond lengths of the chloride series, [H(sebenzimMe)]2MCl2 (M = Zn, Cd, Hg), indicates that while the average M-Cl bond lengths progressively increase as the metal becomes heavier, the variation in M-Se bond length exhibits a non-monotonic trend, with the Cd-Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzimMe)]2CdCl2, [H(sebenzimMe)]3,CdCl2•[H(sebenzim)Me]4CdCl2, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI2 and H(sebenzimMe) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzimMe)]-[H(benzimMe)]CdI2, a transformation that is associated with cleavage of the C-Se bond.

Reactivity of the carbodiphosphorane, (Ph3P)2C, towards main group metal alkyl compounds: coordination and cyclometalation.

The carbodiphosphorane, (Ph3P)2C, reacts with Me3Al and Me3Ga to afford the adducts, [(Ph3P)2C]AlMe3 and [(Ph3P)2C]GaMe3, which have been structurally characterized by X-ray diffraction. (Ph3P)2C also reacts with Me2Zn and Me2Cd to generate an adduct but the formation is reversible on the NMR time scale. At elevated temperatures, however, elimination of methane and cyclometalation occurs to afford [κ2-Ph3PC{PPh2(C6H4)}]ZnMe and [κ2-Ph3PC{PPh2(C6H4)}]CdMe. Analogous cyclometalated products, [κ2-Ph3P{CPPh2(C6H4)}]ZnN(SiMe3)2 and [κ2-Ph3P{CPPh2(C6H4)}]CdN(SiMe3)2, are also obtained upon reaction of (Ph3P)2C with Zn[N(SiMe3)2]2 and Cd[N(SiMe3)2]2. The magnesium compounds, Me2Mg and {Mg[N(SiMe3)2]2}2, likewise react with (Ph3P)2C to afford cyclometalated derivatives, namely [κ2-Ph3PC{PPh2(C6H4)}]MgN(SiMe3)2 and {[κ2-Ph3PC{PPh2(C6H4)}]MgMe}2. While this reactivity is similar to the zinc system, the magnesium methyl complex is a dimer with bridging methyl groups, whereas the zinc complex is a monomer. The greater tendency of the methyl groups to bridge magnesium centers rather than zinc centers is supported by density functional theory calculations.

Zerovalent Nickel Compounds Supported by 1,2-Bis(diphenylphosphino)benzene: Synthesis, Structures, and Catalytic Properties.

Zerovalent nickel compounds which feature 1,2-bis(diphenylphosphino)benzene (dppbz) were obtained via the reactivity of dppbz towards Ni(PMe3)4, which affords sequentially (dppbz)Ni(PMe3)2 and Ni(dppbz)2. Furthermore, the carbonyl derivatives (dppbz)Ni(PMe3)(CO) and (dppbz)Ni(CO)2 may be obtained via the reaction of CO with (dppbz)Ni(PMe3)2. Other methods for the synthesis of these carbonyl compounds include (i) the formation of (dppbz)Ni(CO)2 by the reaction of Ni(PPh3)2(CO)2 with dppbz and (ii) the formation of (dppbz)Ni(PMe3)(CO) by the reaction of (dppbz)Ni(CO)2 with PMe3. Comparison of the ν(CO) IR spectroscopic data for (dppbz)Ni(CO)2 with other (diphosphine)Ni(CO)2 compounds provides a means to evaluate the electronic nature of dppbz. Specifically, comparison with (dppe)Ni(CO)2 indicates that the o-phenylene linker creates a slightly less electron donating ligand than does an ethylene linker. The steric impact of the dppbz ligand in relation to other diphosphine ligands has also been evaluated in terms of its buried volume (%Vbur) and steric maps. The nickel center of (dppbz)Ni(PMe3)2 may be protonated by formic acid at room temperature to afford [(dppbz)Ni(PMe3)2H]+, but at elevated temperatures, effects catalytic release of H2 from formic acid. Analogous studies with Ni(dppbz)2 and Ni(PMe3)4 indicate that the ability to protonate the nickel centers in these compounds increases in the sequence Ni(dppbz)2 < (dppbz)Ni(PMe3)2 < Ni(PMe3)4; correspondingly, the pKa values of the protonated derivatives increase in the sequence [Ni(dppbz)2H]+ < [(dppbz)Ni(PMe3)2H]+ < [Ni(PMe3)4H]+. (dppbz)Ni(PMe3)2 and Ni(PMe3)4 also serve as catalysts for the formation of alkoxysilanes by (i) hydrosilylation of PhCHO by PhSiH3 and Ph2SiH2 and (ii) dehydrocoupling of PhCH2OH with PhSiH3 and Ph2SiH2.

Flexibility of the Carbodiphosphorane, (Ph3P)2C: Structural Characterization of a Linear Form.

X-ray diffraction studies demonstrate that crystals of the carbodiphosphorane, (Ph3P)2C, obtained from solutions in benzene, exhibit a linear P-C-P interaction. This observation is in contrast to the highly bent structures that have been previously reported for this molecule, thereby providing experimental evidence that the coordination geometry at zerovalent carbon may be very flexible. Density functional theory calculations support the experimental observations by demonstrating that the energy of (Ph3P)2C varies relatively little over the range 130-180°.

Tris(2-mercaptoimidazolyl)hydroborato Cadmium Thiolate Complexes, [TmBut]CdSAr: Thiolate Exchange at Cadmium in a Sulfur-Rich Coordination Environment.

A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [TmBut]CdSAr, have been synthesized by the reactions of [TmBut]CdMe with ArSH (Ar = C6H4-4-F, C6H4-4-But, C6H4-4-OMe, and C6H4-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [TmBut]CdSPy and [TmBut]CdSePy have been obtained via the respective reactions of [TmBut]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [TmBut]CdSAr and [TmBut]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS4] motif is distorted tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [TmBut]CdSPy and [TmBut]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms. The ability of the thiolate ligands to participate in exchange was probed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopic studies of the reactions of [TmBut]CdSC6H4-4-F with ArSH (Ar = C6H4-4-But or C6H4-4-OMe), which demonstrate that (i) exchange is facile and (ii) coordination of thiolate to cadmium is most favored for the p-fluorophenyl derivative. Furthermore, a two-dimensional EXSY experiment involving [TmBut]CdSC6H4-4-F and 4-fluorothiophenol demonstrates that degenerate thiolate ligand exchange is also facile on the NMR time scale.

Crystal structure of di-µ-chlorido-bis-[chlorido-bis-(1,2-dimethyl-5-nitro-1H-imidazole-κN3)copper(II)] acetonitrile disolvate.

1,2-Dimethyl-5-nitro-imidazole (dimetridazole, dimet) is a compound that belongs to a class of nitro-imidazole drugs that are effective at inhibiting the activity of certain parasites and bacteria. However, there are few reports that describe structures of compounds that feature metals complexed by dimet. Therefore, we report here that dimet reacts with CuCl2·H2O to yield a chloride-bridged copper(II) dimer, [Cu2Cl4(C5H7N3O2)4] or [Cu(µ-Cl)Cl(dimet)2]2. In this mol-ecule, the CuII ions are coordinated in an approximately trigonal-bipyramidal manner, and the mol-ecule lies across an inversion center. The dihedral angle between the imidazole rings in the asymmetric unit is 4.28 (7)°. Compared to metronidazole, dimetridazole lacks the hy-droxy-ethyl group, and thus cannot form inter-molecular O⋯H hydrogen-bonding inter-actions. Instead, [Cu(µ-Cl)Cl(dimet)2]2 exhibits weak inter-molecular inter-actions between the hydrogen atoms of C-H groups and (i) oxygen in the nitro groups, and (ii) the terminal and bridging chloride ligands. The unit cell contains four disordered aceto-nitrile mol-ecules. These were modeled as providing a diffuse contribution to the overall scattering by SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18], which identified two voids, each with a volume of 163 Å3 and a count of 46 electrons, indicative of a total of four aceto-nitrile mol-ecules. These aceto-nitrile mol-ecules are included in the chemical formula to give the expected calculated density and F(000).

Synthesis, structure and reactivity of [Tm(Bu(t))]ZnH, a monomeric terminal zinc hydride compound in a sulfur-rich coordination environment: access to a heterobimetallic compound.

The first terminal zinc hydride complex that features a sulfur-rich coordination environment, namely the tris(2-mercapto-1-tert-butylimidazolyl)hydroborato compound, [Tm(Bu(t))]ZnH, has been synthesized via the reaction of [Tm(Bu(t))]ZnOPh with PhSiH3. The Zn-H bond of [Tm(Bu(t))]ZnH is subject to insertion of CO2 and facile protolytic cleavage, of which the latter provides access to heterobimetallic [Tm(Bu(t))]ZnMo(CO)3Cp.

Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg-C Bond Cleavage and Phenylselenolate Exchange.

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg-C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg-C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg-SePh/Hg-X groups rather than metathesis of the Hg-R/Hg-R groups.

Crystal structure of metronidazolium tetra-chlorido-aurate(III).

Metronidazole (MET) [systematic names: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole and 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol] is a medication that is used to treat infections from a variety of anaerobic organisms. As with other imidazole derivatives, metronidazole is also susceptible to protonation. However, there are few reports of the structures of metronidazolium derivatives. In the title compound, (C6H10N3O3)[AuCl4] [systematic name: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazol-3-ium tetra-chlorido-aur-ate(III)], the asymmetric unit consists of a metronidazolium cation, [H(MET)](+), and a tetra-chlorido-aurate(III) anion, [AuCl4](-), in which the Au(III) ion is in a slightly distorted square-planar coordination environment. In the cation, the nitro group is essentially coplanar with the imidazole ring, as indicated by an O N-C=C torsion angle of -0.2 (4)°, while the hy-droxy-ethyl group is in a coiled conformation, with an O(H)-C-C-N torsion angle of 62.3 (3)°. In the crystal, the anion and cation are linked by an inter-molecular O-H⋯Cl hydrogen bond. In addition, the N-H group of the metronidazolium ion serves as a hydrogen-bond donor to the O atom of the hy-droxy-ethyl group of a symmetry-related mol-ecule, leading to the formation of chains along [010].

Exchange of Alkyl and Tris(2-mercapto-1-t-butylimidazolyl)hydroborato Ligands Between Zinc, Cadmium and Mercury.

The tris(2-mercaptoimidazolyl)hydroborato ligand, [TmBut ], has been used to investigate the exchange of alkyl and sulfur donor ligands between the Group 12 metals, Zn, Cd and Hg. For example, [TmBut ]2Zn reacts with Me2Zn to yield [TmBut ]ZnMe, while [TmBut ]CdMe is obtained readily upon reaction of [TmBut ]2Cd with Me2Cd. Ligand exchange is also observed between different metal centers. For example, [TmBut ]CdMe reacts with Me2Zn to afford [TmBut ]ZnMe and Me2Cd. Likewise, [TmBut ]HgMe reacts with Me2Zn to afford [TmBut ]ZnMe and Me2Hg. However, whereas the [TmBut ] ligand transfers from mercury to zinc in the methyl system, [TmBut ]HgMe/Me2Zn, transfer of the [TmBut ] ligand from zinc to mercury is observed upon treatment of [TmBut ]2Zn with HgI2 to afford [TmBut ]HgI and [TmBut ]ZnI. These observations demonstrate that the phenomenological preference for the [TmBut ] ligand to bind one metal rather than another is strongly influenced by the nature of the co-ligands.

Synthesis and structures of cadmium carboxylate and thiocarboxylate compounds with a sulfur-rich coordination environment: carboxylate exchange kinetics involving tris(2-mercapto-1-t-butylimidazolyl)hydroborato cadmium complexes, [Tm(Bu(t))]Cd(O2CR).

A series of cadmium carboxylate compounds in a sulfur-rich environment provided by the tris(2-tert-butylmercaptoimidazolyl)hydroborato ligand, namely, [Tm(Bu(t))]CdO2CR, has been synthesized via the reactions of the cadmium methyl derivative [Tm(Bu(t))]CdMe with RCO2H. Such compounds mimic aspects of cadmium-substituted zinc enzymes and also the surface atoms of cadmium chalcogenide crystals, and have therefore been employed to model relevant ligand exchange processes. Significantly, both (1)H and (19)F NMR spectroscopy demonstrate that the exchange of carboxylate groups between [Tm(Bu(t))]Cd(κ(2)-O2CR) and the carboxylic acid RCO2H is facile on the NMR time scale, even at low temperature. Analysis of the rate of exchange as a function of concentration of RCO2H indicates that reaction occurs via an associative rather than dissociative pathway. In addition to carboxylate compounds, the thiocarboxylate derivative [Tm(Bu(t))]Cd[κ(1)-SC(O)Ph] has also been synthesized via the reaction of [Tm(Bu(t))]CdMe with thiobenzoic acid. The molecular structure of [Tm(Bu(t))]Cd[κ(1)-SC(O)Ph] has been determined by X-ray diffraction, and an interesting feature is that, in contrast to the carboxylate derivatives [Tm(Bu(t))]Cd(κ(2)-O2CR), the thiocarboxylate ligand binds in a κ(1) manner via only the sulfur atom.