Palladium Complexes Comprising C(4)-bound Diimidazolylidene Carbenes

Abstract

Imidazolium-derived palladium dicarbene complexes have been synthesized which feature either normal C(2) carbene bonding or abnormal C(4) bonding. Comparison of the reactivity of these complexes, in particular towards Lewis acids (H+, Ag+), indicate consistently that C(4)-bound carbenes are stronger donors than their C(2)-bound analogs. As a consequence of this electronic impact, palladium complexes comprising C(4)-bound dicarbene ligands were found to be efficient catalysts for olefin hydrogenation under mild conditions.