Direct Comparison of Hydrogenation Catalysis by Intact versus Fragmented Triruthenium Clusters

The solvent plays a pivotal role in controlling the selectivity of the catalytic hydrogenation of alkenes and alkynes by [Ru3(CO)12−x(PPh3)x] (x=1 or 2) with the mechanism varying with the solvent polarity. In polar solvents the reaction proceeds via H2 addition products based on [Ru3(H)(μ-H)(CO)9(PPh3)2], as demonstrated by parahydrogen-induced polarization (PHIP). In nonpolar solvents catalysis by [RuH2(CO)2(PPh3)(substrate)], resulting from fragmentation, competes with that by the intact cluster.