Hydrido-bridged bimetallic complexes involving gold or silver and chromium, molybdenum, or tungsten: X-ray crystal structure of [AuCr(µ-H)(CO)5(PPh3)]

Abstract

Treatment of tetrahydrofuran solutions of the salts [N(PPh₃)₂][MH(CO)₄L][M = Cr or W, L = CO; M = W, L = P(OMe)₃] with [AuCl(PPh₃)] in the presence of TIPF₆ afforded the compounds [AuM(µ-H)(CO)₄L(PPh₃)]. The gold–molybdenum compound [AuMo(µ-H)(CO)₅(PPh₃)] was similarly prepared from a dichloromethane solution of [N(PPh₃)₂][Mo₂(µ-H)(CO)₁₀]. Reactions between [N(PPh₃)₂][MH(CO)₄L][M = Cr or W, L = CO; M = W, L = P(OMe)₃], [Agl(PMe₃)], and TIPF₆ yielded the hydrido-bridged bimetal compounds [AgM(µ-H)(CO)₄L(PMe₃)]. A single-crystal X-ray diffraction study has been carried out on the complex [AuCr(µ-H)(CO)₅(PPh₃)]. The molecule has a bent Au(µ-H) Cr geometry [Au–Cr 2.770(2), Au–H 1.72(11), and Cr–H 1.64(12)Å; Au–H–Cr 111 (5)°] in accord with the presence of a three-centre two-electron bond. The orientation of the Cr(CO)₅ group is staggered relative to the Au(µ-H)Cr bridge, with the hydrido-ligand lying transoid to the axial carbonyl ligand and the phosphine group. Crystals are triclinic, space group P(no. 2), and the structure has been refined to R 0.047 for 3 401 intensities measured at 210 K in the range 4 ⩽ 2θ⩽ 50°. Proton, ³¹P-{¹H}, and ¹³C-{H} n.m.r. spectroscopic data for the various compounds are reported and show that these species undergo dynamic behaviour in solution involving dissociation of the PPh₃ or PMe₃ groups, site exchange of CO ligands, and, for the silver-containing complexes, dissociation of the MH(CO)₄L fragments.