Dynamical density functional study of acetylene to vinylidene isomerization in (Cp)(CO)2Mn(HC≡CH)

The acetylene to vinylidene isomerization in (CP)(CO)(2)Mn(HCequivalent toCH) has been investigated by both static and dynamic density functional calculations. The potential energy surface for the conversion of coordinated acetylene to vinylidene has been analyzed by a gradient-corrected DFT approach. The eta(1)-vinylidene complex has been found 9.0 kcal mol(-1) more stable than the acetylene complex and is the thermodynamically most stable species of this reaction system. An unprecedented eta(2)-vinylidene species has been characterized and found 38.4 kcal mol(-1) higher than the corresponding eta(1)-isomer. The direct 1,2 hydrogen shift, proceeding via an agostic intermediate, is the energetically most favorable path, with a free energy barrier of 27.3 kcal mol(-1). The higher barrier computed for the oxidative addition leading to the corresponding alkynylhydrido complex (35.0 kcal mol(-1)) rules out the intermediacy of such a species in the investigated process. Dynamics simulations have also been performed on the (CP)(CO)(2)Mn(HCequivalent toCH) complex in order to study the detailed features of the possible acetylene to vinylidene conversion pathways and show that the isomerization effectively takes place through a direct 1,2 hydrogen shift from the agostic intermediate.