HOMOGENEOUS MULTIMETALLIC CATALYSTS .10. FORMYLATION OF ARYL AND ALKENYL IODIDES BY PALLADIUM RUTHENIUM BIMETALLIC CATALYSTS

The PdCl2(PPh3)2-Ru3(CO)12 bimetallic system exhibited higher catalytic activity for the formylation of aryl and alkenyl iodides than PdCl2(PPh3)2 or Ru3(CO)12 alone. Thus, in the formylation of iodobenzene (at 70-degrees-C for 1.5 h under 50:50 atm of CO:H-2), the yield of benzaldehyde by PdCl2(PPh3)2-Ru3(CO)12 catalyst (Pd:Ru = 1:2) was about four times as high as that by PdCl2(PPh3)2 alone. Carbonyl complexes of other metals, such as Mn2(CO)10, Co(CO)8, Cr(CO)6, Fe(CO)5, Mo(CO)6 and W(CO)6 were ineffective as the second component of the catalyst. To clarify the mechanism of the synergistic effects, the reaction of PdI(CO-p-Tol)(PPh3)2 with [HRu3(CO)11]- or [HRu(CO)4]-, ruthenium hydride species known to be generated under the catalytic formylation conditions, was performed. The reaction rapidly proceeded at 40-degrees-C nuclear reductive elimination to form p-tolualdehyde, although the reaction with molecular hydrogen was very slow. These results strongly suggest that the improved catalytic activity of the Pd-Ru system is attributable to the high hydrogenolysis activity of in-situ-generated ruthenium hydride species.