Organometallic Ruthenium Complexes: Application in the Olefination of Carbonyl Compounds
Ruthenium compounds of general formula Cp‘RuX(PR2R‘)2 (Cp‘ = η5-C5H5 (Cp), η5-C9H7 (Ind), η5-C5(CH3)5 (Cp*); X = Cl, CF3C(O)O; R = C6H5 (Ph), C6H4(CH3) (m-tolyl); R‘ = C6H5, C6H11 (Cy), C6H4(CH3) (m-tolyl, o-tolyl)) are examined as catalysts for the aldehyde olefination starting from diazo compounds, phosphanes, and aldehydes. Cp*RuCl(PPh3)2 is highly active for the olefination of several aldehydes, displaying a very high E-selectivity, as well as for ketone olefination (with benzoic acid as cocatalyst). The reaction's mechanism is substantiated by the isolation of a catalytic active reaction species, namely, a mixed carbene/phosphane ruthenium complex, Cp*RuCl(CHCO2Et)(PPh3) (8). Spectroscopic studies reveal that the latter compound reacts with PPh3 to produce the phosphorus ylide Ph3PCHCO2Et, which further reacts with the aldehyde to produce the olefin.