Investigating Pathways of Molecular H2 Exchange in (μ-H)2Os3(CO)10

The occurrence of two pathways responsible for the reaction of (mu -H)(2)Os-3(CO)(10) with molecular hydrogen-has been elucidated by comparing the results obtained from H-2/D-2 isotopic exchange experiments and para-H-2 effects observed in the cluster's H-1 NMR spectrum. The most efficient exchange process is based on an associative mechanism that leads to the formation of the elusive (eta-*H-2)(H)(mu -H)Os-3(CO)(10) species (*H-2 is either a D-2 or a para-H-2 molecule), which undergoes *H-H elimination. The other pathway (whose efficiency increases with temperature) is based on the dissociation of H-2 from (mu -H)(2)Os-3(CO)(10) to form the highly unsaturated "OS3(CO)(10)" moiety, which promptly adds a *H-2 molecule, yielding the asymmetrical *H(mu-*H)Os-3(CO)(10)S intermediate (where S is a stabilizing solvent molecule), which releases the S molecule to re-form (mu-*H)(2)Os-3-(CO)(10).