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

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.