Abstract

The cationic complex [OsH(CO)(NCMe)(2)(PPh3)(2)](+) (4), isolated as its BF4- salt, was synthesized in high yields by reaction of OsHCl(CO)(PPh3)(3) (3) with acetonitrile in the presence of NaBF4. The spectroscopic data are consistent with an octahedral geometry around the osmium atom, with two phosphines mutually trans and the acetonitriles mutually cis. Complex 4 is shown to be an efficient precatalyst for the hydrogenation of benzaldehyde, cyclohexanone, cyclohexene and quinoline. For the hydrogenation of carbonyl compounds to their corresponding alcohols in 2-methoxyethanol, complex 4 showed a catalytic activity somewhat lower than 3 and than their analogous complexes of ruthenium. However, for the hydrogenation of cyclohexene to cyclohexane and for the quinoline reduction to 1,2,3,4-tetrahydroquinoline, in xylene solvent, the activities were higher for the osmium complexes. The results show that the cationic osmium complex is a more efficient precatalyst for the hydrogenation of C=C and C=N bonds than for C=O bonds in selected substrates.