A comparison of phosphaferrocene and phospharuthenocene ligands in Rh+-catalysed enamide hydrogenation reactions:: Superior performance of the phospharuthenocene
Enantiopure Cp*-substituted 3,4-dimethyl-5-phenylphosphametallo-cene-2-methanols (M=Fe, Ru) have been prepared from the corresponding 2-carboxy-(-)-menthylphospholide anion and elaborated into 2-CH2PPh2 phosphametallocenes (13: M=Fe; 14: M=Ru) and 2-CH2PtBuR substituted phospharuthenocenes (R=tBu, Me). The crystal structures of complexes [Rh(1,5-cod)(eta(2)-L)]+BF4- (L=13, 14) reveal significantly different aryl group configurations. Comparative studies of the hydrogenation of para-substituted N-acetylcinnamate esters with these pre-catalysts show a superior performance for the phospharuthenocene derivative in terms of both rate and enantioselectivity.