Cyclometalated Dicarbonyl Ruthenium Catalysts for Transfer Hydrogenation and Hydrogenation of Carbonyl Compounds

摘要

The dicarbonyl complex RuCl2(L)(2)(CO)(2) (l) was easily prepared by reaction of ruthenium chloride hydrate with formic acid and L (L = (2,6-Me2C6H3)PPh2) in ethanol at reflux, via the [RuCl2(CO)(2)](n) intermediate. Alternatively, 1 was obtained from [RuCl2(CO)(3)](2) and L by CO elimination. Reaction of 1 with NEt3 in toluene at reflux afforded the cyclometalated derivative RuCl{(2-CH2-6-MeC6H3)PPh2}-(L)(CO)(2) (2). A simple one-pot synthesis of 2 was achieved by treatment of RuCl3 hydrate with formic acid, L, and NEt3. The cyclometalated dicarbonyl complexes [Ru{(2-CH2-6-MeC6H3)PPh2}(NN)(CO)(2)]Cl (NN = ethylenediamine, 3; 2-(aminomethyl)pyridine, 4; (R,R)-l,2-diphenylethane-l,2-diamine, 5) were isolated by reaction of 2 with the corresponding dinitrogen ligand in methanol at reflux. Complexes 1-4 catalyze the transfer hydrogenation (TH) of acetophenone in 2-propanol at reflux (S/C = 1000 and TOF up to 30 000 h(-1)) with alkali base (l-5 mol %), whereas 5 leads to (S)-1-phenylethanol with 68% ee. The derivatives 1-5 catalyze the hydrogenation (HY) of several ketones (H-2, 30 bar) at 70 degrees C in MeOH and EtOH with KOtBu (2 mol %) (S/C and TOF up to 25 000 and 14 000 h(-1)). Addition of NN ligands to 1 and 2 in situ increases both the TH and HY activity, with ampy displaying the better performance. Heating of the cationic complex 3 in solid state and in solution leads to decarbonylation, affording the neutral monocarbonyl compound RuCl{(2-CH2-6-MeC6H3)PPh2}(en)(CO) (6) which was found active in the ketone HY.