Mechanism of the homogeneous catalytic hydrogenation using anion-promoted metal clusters

The authors recently reported that anions, in particular isocyanate, were effective in converting normally unreactive Ru/sub 3/(CO)/sub 12/ into an active catalyst (5-6 turnovers/min under ambient conditions) for alkene hydrogenation. While both spectroscopic and kinetic evidence supported a catalytic cycle involving an intact ruthenium triangle, no intermediates were isolated. With the hope of isolating such species, they turned to the osmium system and have found a rich chemistry that is reported here. The authors initially synthesized the anionic osmium isocyanato clusters using the same reaction found successful in the ruthenium chemistry. The osmium cluster chemistry presented here provides evidence for the intermediates proposed. While less active than the ruthenium system, these isocyanate-promoted osmium clusters also catalyze the hydrogenation of olefins.