UNPRECEDENTED TRIMETALLIC CLUSTER WITH AN INPLANE MU-3-HYDRIDE LIGAND - X-RAY CRYSTAL-STRUCTURE OF [MO2(CO)8(MU-DPPM)(MU-3-H)(MU-AUPPH3)]

The salt (NEt4)[Mo2(CO)8(mu-dppm)(mu-H)] [dppm = bis(diphenylphosphino)methane] reacts with XMPPh3 (M = Au, Cu, Ag; X = Cl, I) in tetrahydrofuran to yield [Mo2(CO)8(mu-dppm)(mu3-H)(mu-MPPh3)] (M = Au, 1a; M = Ag, 1b; M = Cu, 1c). The structure of 1a has been determined by X-ray diffraction methods. Crystals are orthorhombic, space group P2(1)2(1)2(1) with Z = 4 in a unit cell of dimensions a = 12.361 (5), b = 15.179 (6), and c = 25.800 (8) angstrom. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 2309 observed reflections to R and R(w) values of 0.0504 and 0.0668, respectively. The structure of 1a is without precedent in that the metal core, consisting of an almost symmetric Mo2Au triangular framework, is held by a hydride ligand located m the same plane defined by the metal atoms. Although an accurate location of this hydride was not possible, there are several lines of evidence in agreement with this position. The Mo-Mo separation is 3.771 (3) angstrom, and the Mo-Au bond lengths are 2.900 (3) and 2.914 (2) angstrom. Reaction of (NEt4)[Mo2(CO)8(mu-dppm)(mu-H)] With (ClAU)2(mu-PP) (PP = dppm, dppe [1,2-bis(diphenylphosphino)ethane], and dppp [1,3-bis(di-phenylphosphino)propane]) leads to the hexametallic complexes [{Mo2(CO)8(mu-dppm)(mu3-H)(mu-Au)}2(PP)] (PP = dppm, 2a; PP = dppe, 2b; PP = dppp, 2c) which contain two metal cluster fragments linked by a bridging diphosphine. The bonding within the Mo2HAu skeleton and the structural differences between 1a and the parent anion [Mo2(CO)8(mu-dppm)(mu-H)]- are explained on the basis of molecular orbital calculations.