Syntheses and characterizations of group 6 metal cyanotrihydroborate complexes

The anions, [M(CO)_6-n(NCBH₃)_n]ⁿ⁻ (n=2, M=Cr(1); n=3, M=Cr(2), Mo(3), W(4)), were prepared either from the reactions of sodium cyanotrihydroborate with group 6 transition metal hexacarbonyls, M(CO)₆ (M=Cr, Mo, W), or through the reactions of M(CO)₃(CH₃CN)₃ (M=Cr, W) with sodium cyanotrihydroborate. The cyanotrihydroborate ligand bonds to the metal through a nitrogen atom, which was confirmed by the Infrared, proton and boron NMR spectroscopies. Crystal structures of the above complexes were determined by single crystal X-ray diffraction analyses. A cis configuration is found in 1. Molecular structures of 2, 3, and 4 are similar and a facial configuration is observed.     

Isolable, gold carbonyl complexes supported by N-heterocyclic carbenes

Cationic gold carbonyl complexes supported by N-heterocyclic carbene ligands, SIDipp and IDipp, have been synthesized. [(SIDipp)Au(CO)][SbF(6)] has a linear, two-coordinate gold center. [(SIDipp)Au(CO)][SbF(6)] and [(IDipp)Au(CO)][SbF(6)] display ?ν(CO) values at 2197 and 2193 cm(-1), respectively. Computational studies on [(SIMe)Au(CO)](+) indicate the presence of a strong Au(I)-CO bond.     

Syntheses and spectroscopic studies on group IIB metal 1,4-benzodiazepine complexes

Summary The preparation and characterization of some zinc(II) and cadmium(II) halide complexes with 1,3-dihydro-7-nitro-5-phenyl-2H-1,4-benzodiazepin-2-one and 7-chloro-l-methyl-5-phenyl-3H-1,4-benzodiazepin-2-one are reported. The complexes have been studied by means of magnetic susceptibility measurements, i.r. and far-i.r. spectra and conductivity measurements. Assignments for metalligand and metal-halide modes have been made. The evidence suggests that the complexes, which contain 1 : 1.5, 1 : 1, 1 : 2 and 1 : 4 metal : ligand stoichiometric ratios, have a pseudotetrahedral symmetry, with the exception of Zn(Mog)₄Br₂ ·₂H₂O which is octahedral.     

Facile synthesis of metal N-heterocyclic carbene complexes

A novel electrochemical procedure for the preparation of metal complexes of N-heterocyclic carbenes using imidazolium salts or corresponding silver-NHC complexes as carbene sources and electrolytes, and metal plates as the sacrificial anodes is described. The procedure is simple and good yielding without the use of expensive or air-sensitive reagents.     

Synthesis of N-heterocyclic carbene rhenium(I) carbonyl complexes

Reaction of aminophosphinimine [RHN(CH(2))(2)N[double bond, length as m-dash]PPh(3)] (R = H, Et) with Re(2)(CO)(10) provided the NH-functionalized carbene rhenium complex [Re(2)(CNHCH(2)CH(2)NR)(CO)(9)] (3a, R = H, 3b, R = Et). Treatment of 3 with Br(2) provided the mono nuclear [Re(CNHCH(2)CH(2)NR)(CO)(4)Br] (1, R = H, 2, R = Et). However, NH-functionalized carbene complexes 1-3 did not undergo N-alkylation with alkyl halides to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)(5)Br] with a carbene donor was employed to prepare [Re(IMes(2))(CO)(4)Br] (6a, IMes(2) = 1,3-di-mesitylimidazol-2-ylidene; 6b, IMes(2) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated NHCs have similar bonding with Re(I) metal centers. Reduction of 6a and 6b with LiEt(3)BH yielded the corresponding hydrido complexes 7a-b [ReH(CO)(4)(IMes(2))], but not 1 and 2. Ligand substitution of 1, 6a and 6b toward 2,2'-bipyridine (bipy) was investigated. Crystal structures of 1, 3a-b, 6a-b and 7b were determined for characterization and comparison.     

Homo- and heteroleptic complexes of four-membered group 13 metal(I) N-heterocyclic carbene analogues with group 10 metal(0) fragments

A series of complexes between recently developed four-membered group 13 metal(I) heterocycles and group 10 metal(0) fragments have been prepared and structurally characterized. One prepared complex, [Pt{Ga[N(Ar)]2CNCy2}3] (Ar = C6H3Pri2-2,6; Cy = cyclohexyl), possesses the shortest Pt-Ga bonds yet reported, the covalent components of which are suggested by theoretical studies to have significant pi character.     

Palladium carbonyl complexes with anions of N-heterocyclic carboxylic and pyridine-2-sulfonic acids

Synthesis, spectral characteristics, and structure of palladium(I) carbonyl complexes containing anions of N-heterocyclic carboxylic acids and pyridine-2-sulfonic acid of the general formula [Pd(CO)(NHC-CO₂)]n/[Pd(CO)(NHC-SO₃)]n, where NHC is an N-heterocycle, were described. The resulting complexes can be attributed to a binuclear structure with bridging or terminal coordination of carbonyl ligands depending on the nature of the substituents in the heterocycle.

     

Synthesis of group 6 metal carbonyl complexes containing oxygen- and sulfur-functionalized 1,2,4-triazoles

Reaction of RCOCH₂Tz and PhCOCH(CH₂SPh)Tz with M(CO)₆ or M(CO)₅THF results in RCOCH₂TzM(CO)₅ and PhCOCH(CH₂SPh)TzM(CO)₅ (R = phenyl or ferrocenyl, Tz = 1,2,4-triazol-1-yl and M = Mo or W). X-ray crystal structure analyses show that the triazolyl group acts as a monodentate ligand through the exodentate nitrogen atom in these complexes. The electrochemical behavior of these complexes has been investigated by cyclic voltammetry.     

Dinuclear group VIB metal carbonyl complexes bridged by bis(diphenylphosphino)alkanes

Reactions of the intermediate W(CO)₅THF, generated photochemically from W(CO)₆ in THF, with Ph₂P(CH₂) _n PPh₂ [ = PP; n = 2 (dppe), 4 (dppb), 6 (dpph), 10 (dppd)] at room temperature in THF solutions gave exclusively bimetallic complexes of the (CO)₅WPPW(CO)₅ type. In addition, complexes bridged by diphosphine ligands of the (CO)₄(pip)MPPM(pip)(CO)₄ type (pip = piperidine; M = Mo, W) were prepared by stirring the (CO)₄M(pip)₂ complexes with bis(diphenylphosphino)alkanes in CH₂Cl₂ solution at ambient temperatures. These new bis(diphenylphosphino)alkane-bridged complexes were characterized by i.r., ¹H- and ³¹P-n.m.r. spectroscopies, as well as by elemental analysis.     

Metal formyl complexes. Hydride transfer to group VIII transition metal carbonyl clusters

The reaction of LiBH(C₂H₅)₃ with Os₃(CO)₁₂ or Ir₄(CO)₁₂ leads to the formation of spectroscopically detectable formyl complexes. In the latter case, the complex is smoothly converted to [Ir₄(CO)₁₁H]^?, an expected decompositioFn complex of the corresponding polynuclear formyl complex, [Ir₄(CO)₁₁CHO]^?.     

Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

Donor group functionalized N-heterocyclic carbenes (NHC) are an important class of ligands used in transition metal complex chemistry. Herein, the growing field of sulfur-functionalized NHC compounds and their respective transition metal complexes are described comprehensively. The sulfur-functionalized NHC compounds are categorized by functional groups such as thiolate, thioether, sulfoxide, thiophene, sulfonate and sulfonamide. Chiral compounds and the hemilabile behaviour of sulfur-functionalized NHC compounds are reported.     

Chiral N-heterocyclic carbene-transition metal complexes in asymmetric catalysis

Syntheses and applications of chiral N-heterocyclic carbenes are reviewed. The common features of successful enantioselective catalysts are identified, and the outlook for further investigations is discussed.     

A stable anionic N-heterocyclic carbene and its zwitterionic complexes

Pyrimidinium beta?nes (1), readily accessible via a straightforward modular synthesis from a formamidine and a monosubstituted malonic acid, are readily deprotonated by nBuLi (or KHMDS) to give the stable carbene species [2]Li+ (abbreviated as maloNHC). The latter represents the archetype of a subgroup of N-heterocyclic carbenes incorporating a malonate as remote anionic functional group within their heterocyclic backbone. While playing the dual role of monodentate 2 e- L type donor and noncoordinating charge carrier X, such ligands are seen to provide a rational route to zwitterionic complexes, as illustrated here by three examples (Rh, Fe, Ag). In particular, the reaction of [2]Li+ with [RhCl(1,5-COD)]2 produces the neutral 14 e- complex Rh(maloNHC)(COD) (3) in which coordinative unsaturation at the metal is relieved in the solid state by an uncommon labile bonding interaction between the Cipso of one of the mesityl arms and the Rh center.     

Synthesis,crystal structures and electrochemical properties of group 6 metal carbonyl anion complexes

A series of [M(CO)₅I]⁻ and [M₂(CO)₁₀I]⁻ anion complexes have been synthesized by the photochemical reaction of PhCH₂N(CH₃)₃I or FcCH₂N(CH₃)₃I (Fc=ferrocenyl) with M(CO)₆ (M = Cr, Mo or W), and characterized by elemental analyses, i.r., ¹H-n.m.r. and ¹³C-n.m.r. spectra in the case of the molybdenum and tungsten complexes. These complexes exhibit considerably different electrochemical behavior, when investigated by cyclic voltammetry. The crystal structures of [PhCH₂N(CH₃)₃][Cr(CO)₅I] and [FcCH₂N(CH₃)₃][W₂(CO)₁₀I] have been determined by X-ray diffraction, indicating that only weak contacts maybe exist between anions and cations by the I...H bond in the former, and there are no direct interactions between anions and cations in the latter.     

Polarizability effect in transition metal carbonyl complexes

The literature date on substituent influence on the carbonyl stretching frequencies (ν), CO stretching force constants (k), as well as ¹³C NMR carbonyl chemical shifts (δ) have been analyzed for 19 series of the transition metal carbonyl complexes. It was established for the first time that the ν, k and δ values depend not only on the inductive and resonance effects but also on the polarizability of substituents. The polarizability contribution ranges up to 37%.     

Syntheses and crystal structures of group 6 metal complexes containing allyl and cyanotrihydroborate groups

Compounds M(η³-C₃H₅)(CO)₂(NCCH₃)₂(NCBH₃) and [N(CH₃)₄]₂[M(η³-C₃H₅)(CO)₂(NCBH₃)₃] (M = Mo, W) were prepared and structurally characterized. In the solid state, the allyl group orients its open face to the two carbonyl groups producing an endo form in the above compounds. In solution, an exo form coexists with an endo form in compound Mo(η³-C₃H₅)(CO)₂(NCCH₃)₂(NCBH₃). The cyanotrihydroborate ligand bonds to the metal through a nitrogen atom. Both of the IR and the 11B NMR spectroscopic data suggest the negative charge of the cyanotrihydroborate ligand on the complex is almost localized on the BH₃ and this negative charge only has small effect on the metal-nitrogen interaction.