Unsaturated bis(phosphido)-bridged heterobimetallic polyhydrides via dihydrogen activation

Hydrogenation (1 atm) of (PCy2)2Re(μ-PCy2)2M(1,5-COD) (M = Rh, Ir; Cy = cyclohexyl; COD = cyclooctadiene), (PCy2)2Re(μ-PCy2)2Rh(DMPE) (DMPE = [Me2PCH2]2), [(PCy2)2ReH(μ-PCy2)2Rh(DMPE)]BF4 and (PCy2)2ReH(μ-PCy2)2Pd-(PPh3) proceeds stepwise with initial additions of H2 across the Re = P multiple bonds to give ReH(PCy2H) moieties. Further addition of H2 occurs only for M = Rh. The DMPE complex gives the tetrahydride (PCy2H)2ReH3(μ-PCy2)2RhH(DMPE), which loses PCy2H at 80 °C to give (PCy2H)ReH4(μ-PCy2)2Rh(DMPE). Hydrogenation of the COD complex affords the stable hexahydride (PCy2H)ReH5(μ-PCy2)2RhH(PCy2H) via the cyclooctenyl complex. (PCy2)2ReH(μ-PCy2)2Rh(η3-C8H13). While the hexahydride is an active homogeneous catalyst precursor for the hydrogenation of alkenes, dienes, and alkynes, attempts to activate the Re center for C-H bond activation have not yet been successful. 31P and 1H DNMR spectroscopy have been used to investigate the solution dynamics of the heterobimetallic polyhydrides, and several X-ray diffraction studies serve to define the solid state structures.

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