Effect of the Para-substituent of the Tridentate Pyridine-based Ru(II) Complex upon the Catalytic Activity in Transfer Hydrogenation

Three stable 4-substituted pyridine-based ruthenium(II) complexes [RuCl2(PPh3)L] (L = 4-R-2,6-bis (diethylaminomethylene)pyridine, R = Br, H or allyloxy) were synthesized. The catalytic activities of the complexes toward transfer hydrogenation from alcohols to ketones were investigated. The electronic effects of the para-substituent in the pyridyl ring were probed and we found that the electron-donating group increased the catalytic activity. The result suggests that an electron-donating group is probably preferential for linking the catalytic ruthenium complex and the chemically inert supporting molecules such as a carbosilane dendrimer.