Chiral hexarhodium carbonyl clusters containing heterobidentate phosphine ligands;: a structural and reactivity study

Some intrinsically chiral [Rh-6(CO)(14)(mu,kappa(2)-PX)] clusters have been synthesized, beginning with reactions of [Rh-6(CO)(16-x)(NCMe)x] (x = 1, 2) with PX, where PX represents the bidentate bridging ligands diphenyl(benzothienyl) phosphine (1), diphenyl(2-thienyl) phosphine (2), di(2-thienyl) phenylphosphine (3), tris(2-thienyl) phosphine (4), diphenyl(2-pyridyl) phosphine (5) and diphenylvinylphosphine (6). The ligand tris(2-furyl) phosphine (7) shows no bridging capability. When x = 1 the initial products are the clusters [Rh-6(CO)(15)(kappa(1)-PX)] which undergo spontaneous CO loss to form [Rh-6(CO)(14)(mu,kappa(2)-PX)]. The structures of the [Rh-6(CO)(15)(kappa(1)-PX)] clusters have been elucidated by IR, NMR spectroscopy and FAB-MS spectrometry, and have been found to involve phosphorus atom coordination to a rhodium atom. In addition, the solid state structures of the [Rh-6(CO)(14)(mu,kappa(2)-Ph2P(2-benzothienyl))] (8), [Rh-6(CO)(14)(mu,kappa(2)-Ph2P(2-thienyl))] (9), [Rh-6(CO)(14)(mu,kappa(2)-PhP(2-thienyl)(2))] (10) and [Rh-6(CO)(14)(mu,kappa(2)-Ph2P(pyridyl))] (12) clusters have been determined by X-ray crystallography. The various types of chirality exhibited by these clusters are discussed. A simple model is proposed to account for the ratios of stereochemical isomers found in the Rh-6(CO)(14)(mu,kappa(2)-PhP(2-thienyl)(2) cluster. The kinetics of formation of the bridged clusters from the monosubstituted [Rh-6(CO)(15)(kappa(1)-PX)] clusters have been studied.