Theoretical Study of the Catalytic Cycle for Ethylene Hydrogenation on a Dipalladium Cluster

A theoretical study of the potential energy surface is carried out for the catalytic cycle of ethylene hydrogenation on a Pd₂cluster using the reaction-path Hamiltonian. The catalytic cycle consists of five related reactions involving ten stationary points. The isomerization of the bridged Pd₂H₂complex into the transcomplex with a maximal barrier of 21.5 kcal/mol rather than the activation of the H–H bond is the most important reaction step. A conclusion is drawn that catalysts based on dipalladium complexes in which the dihydride product readily forms a transform can be active in ethylene hydrogenation.