New Ruthenium Complexes in the Catalytic Hydrogenation of Alkynes. Study of Structure and Mechanism

The reaction of [(η5-Ph4C4COHOCC4Ph4-η5)(μ-H)[(CO)4Ru2] (1) with several alkynes was studied. Two new types of Ru complexes, [(η5-Ph4C4CO)(CO)2RuC(Ph)=CPh] (6) and [(η5-Ph4C4COH)(CO)2 RuC(CO2Me)=CHCO2Me] (7), were isolated and structurally characterized by single-crystal X-ray crystallography. These complexes were found to be implicated in the hydrogenation of alkynes with 1 as a catalyst precursor. While complex 7 was found to function as a catalyst in the hydrogenation cycle, complex 6 acts as a catalysis poison by virtue of its stability and irreversible formation. A catalytic cycle has been proposed.