H/D isotopic exchange on the surface of a triosmium carbonyl cluster

The reactions of both Os-3(CO)(10)(NCCH3)(2) and Os-3(CO)(11)(NCCH3) with HD Or with a mixture of H-2/D-2 in chloroform solution at room temperature afford a mixture of H2Os3(CO)(10) (Ia), HDOs3(CO)(10) (Ib), and D2Os3(CO)(10) (Ic). The three isotopomers are also obtained by reacting H2Os3(CO)(10) with D-2. By measurement of the rates of disappearance of Ia in the latter reaction at four different temperatures, the thermodynamic parameters have been estimated (E(a) = 43.7 kJ/mol, Delta H-double dagger = 41.2 kJ/mol, Delta S-double dagger = -0.17 kJ/(mol K)). No H/D isotopic exchange has been observed after heating Ia and Ic in toluene for several hours. A mechanism involving the reversible oxidative addition and reductive elimination of molecular hydrogen on H2Os3(CO)(10) via the formation of a fluxional tetra(hydrido, deuterio) intermediate is proposed.