Cooperative P–H Bond Activation with Ruthenium and Iridium Carbene Complexes

Abstract

The reactivity of nucleophilic ruthenium and iridium carbene complexes toward the P–H bond in secondary phosphines and phosphine oxides was studied. While the reactions of the free phosphines resulted in the formation of product mixtures, the oxidized congeners gave way to fast and selective P–H bond activation reactions by means of metal–ligand cooperation and net addition of the P–H bond across the metal–carbon double bond. The formed phosphoryl complexes were characterized in the solid state and in solution, indicating C–H···O hydrogen bonding as a structural motif. Computational studies to provide insights into the reaction mechanism revealed that—in contrast to other E–H bond activation reactions with carbene complexes—no concerted 1,2-addition across the M═C bond is operative. Instead, the P–H bond activation of the phosphine oxides preferably proceeds via coordination of the phosphinous acid tautomer to the metal, followed by hydrogen transfer to the carbenic carbon atom.