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

The reaction of [(η 5 -Ph 4 C 4 COHOCC 4 Ph 4 -η 5 )(μ-H)[(CO) 4 Ru 2 ] ( 1 ) with several alkynes was studied. Two new types of Ru complexes, [(η 5 -Ph 4 C 4 CO)(CO) 2 RuC(Ph)=CPh] ( 6 ) and [(η 5 -Ph 4 C 4 COH)(CO) 2 RuC(CO 2 Me)=CHCO 2 Me] ( 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.