The silica-supported cluster Os3(CO)10(μ-H)(μ-OSi⋖) (1) efficiently catalyzes the hydrogenation of ethylene under mild reaction conditions; the reaction is zero order in ethylene and first order in hydrogen. The reaction kinetics as well as volumetric and IR studies of the interaction of 1 with C2H4, H2, and CO indicate a mechanism involving the intact triosmium framework in all the elementary steps conforming the catalytic cycle. The facile 3e-⇄1e- interconversion of surface-oxygen ligands provides the appropriate energy balance for cluster catalysis without fragmentation. The reactivity of the molecular analogue Os3(CO)10(μ-H)(μ-OPh) (2) toward C2H4 and H2 has also been studied by IR and NMR spectroscopy, and the data are in agreement with the proposed hydrogenation cycle for 1. However, in contrast with 1, 2 is quickly transformed in solution under catalytic conditions with loss of phenol and formation of H2Os3(CO)10 and H4Os4(CO)12. This difference of behavior indicates the stabilizing influence of the silica support.
ASJC Scopus subject areas
- Colloid and Surface Chemistry