Homogeneous catalysis on metal clusters. The isomerization and selective hydrogenation of dienes, alkenes, and alkynes in the presence of [(η-C5H5)NiOs3(µ-H)3(CO)9] and [(η-C5H5)NiOs3(µ-H)3(CO)8L][L = PPh2H or P(C6H4Me-o)3]. Spectroscopic identification of the reaction intermediates and X-ray structure of [Os3(µ-H)(CO)9(MeCCHCMe)]

Abstract

The complexes [(η-C₅H₅)NiOs₃(µ-H)₃(CO)₉] and [(η-C₅H₅)NiOs₃(µ-H)₃(CO)₈L][L = PPh₂H or P(C₆H₄Me-o)₃] catalyze under homogeneous conditions the hydrogenation of one double bond of dienes and show selectivity in the hydrogenation of triple and double C–C bonds; non-conjugated dienes are isomerized. Experimental evidence suggests that the cluster acts as a catalyst. Complexes [(η-C₅H₅)NiOs₃(µ-H)₃(CO)₈(diene)] and [Os₃(µ-H)(CO)₉(MeCCHCMe)] have been isolated in the reaction solutions. The former complexes have been identified by spectroscopy and the latter by X-ray diffraction methods. A reaction path is proposed. Crystals of [Os₃(µ-H)(CO)₉(MeCCHCMe)] are monoclinic, space group P2₁/n, with unit-cell dimensions a= 10.960(7), b= 17.064(8), c= 10.162(5)Å, β= 106.07(2)°, and Z= 4. The structure was determined from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.048. In the complex an allylic ligand (derived from a pentadiene) co-ordinated to a triangular osmium cluster has been found; although this type of structure has already been reported, this is the first osmium complex obtained by reaction with a diene.