A mechanistic study of the reaction of H2Os3(CO)10 with terminal alkynes

Crossover expts. using X2Os3(CO)10 and XCCCMe3(X = H or D) were conducted and the effects of deuterium substitution on the product distribution noted. A kinetic isotope effect is obsd. on the rate of formation of (.mu.-H)Os3(CO)10(trans-.sigma.-.pi.-.eta.2-.mu.-CH:CHR) (I) relative to the other two products of the reaction (.mu.-H)Os3(CO)10(.sigma.-.pi.-.eta.2-.mu.-C:CR) (II) and (.mu.-CO)Os3(CO)9(.eta.2-.mu.3-HCCR) (III). The crossover expts. demonstrate that II and III are not formed from I. A mechanism is presented which explains these results as well as the obsd. scrambling of H and D in the formation of I in terms of an extension of the known ligand dynamics of H2Os3(CO)10L complexes.