Understanding metal-free catalytic hydrogenation: A systematic theoretical study of the hydrogenation of ethene

Metal-free catalytic hydrogenation of ethene has been examined using high-level [G3(MP2)-RAD] ab initio molecular orbital theory. The dependence of the catalytic activity on the nature of the catalyst Z-X-H has been explored. We find that the catalytic activity is generally greater as Z-X-H becomes more acidic, both for first- and second-row atoms X. Molecules in which X is a second-row atom generally lead to more effective catalysis than the corresponding first-row analogues. The proton affinity at X of Z-X-H also contributes significantly to the catalysis in some cases (e.g. amines).