Addition and elimination of hydrogen and ligand substitution on triosmium clusters. Kinetics and mechanism

Abstract

The kinetics of the reversible reaction HOs 3(μ-COMe)(CO) 10 + H 2 ⇌ H 3Os 3(μ 3-COMe)(CO) 9 + CO has been investigated. The reaction of HOs 3(μ-COMe)(CO) 10 with hydrogen involves dissociation of a CO ligand prior to the rate-determining step, which is proposed to be the oxidative addition of molecular hydrogen. The reaction of H 3Os 3(μ 3-COMe)(CO) 9 with CO involves rate-limiting hydrogen loss. The equilibrium constant and the competition ratio for hydrogen and CO for the unsaturated intermediate were determined. The mechanism of substitution by AsPh 3 on HOs 3(μ-COMe)(CO) 10 also involves a CO dissociative mechanism. Based upon relative rate constants for CO, AsPh 3, and hydrogen addition to HOs 3(COMe)(CO) 9, CO dissociation and hydrogen addition are proposed to occur at different metal sites.