Dimolybdenum-tin derivatives of the unsaturated hydride [Mo2(η5-C5H5)2(μ-H)(μ-PCy2)(CO)2] and HSnR3 (R = Ph, Bu):: Bridging versus terminal coordination of the triorganostannyl group

Reaction of the 30-electron hydride [Mo2Cp2(mu-H)(mu-PCy2)(CO)(2)] with HSnR3 (Cp = eta(5)-C5H5; R = Ph, Bu) leads to the unsaturated dimolybdenum-tin derivatives [Mo2Cp2(mu-PCy2)(mu-SnR3)(CO)(2)] (R = Ph, Bu), which display a triorganostannyl ligand unusually bridging two metal atoms, and to the phosphine-hydride complex [Mo2Cp2(mu-H)(SnPh3)(CO)(2)(PCy2H)], which has a formally triple Mo-Mo bond bridged by only one hydride ligand. The structures of the triphenylstannyl compounds were determined by single-crystal X-ray diffraction studies, which revealed the presence of short Mo-Mo separations (< 2.6 angstrom), consistent with the presence of metal-metal multiple bonding in these 30-electron derivatives. The phosphine-hydride complex experiences spontaneous dehydrogenation at room temperature to give [Mo2Cp2(mu-PCy2)(mu-SnPh3)(CO)(2)], whereby the terminal SnPh3 group moves into a bridging position. In contrast, carbonylation of the latter stannyl-bridged compound gives an unstable tricarbonyl derivative, [Mo2Cp2(mu-PCy2)(SnPh3)(CO)(3)], and then the stable tetracarbonyl [Mo2Cp2(mu-PCy2)(SnPh3)(CO)(4)] (Mo-Mo) 3.202(1) angstrom), both of which display a terminal stannyl group.