Catalytic transfer hydrogenation of ketones by the use of ruthenium complexes incorporating the new tridentate ligand, bis(2-oxazolin-2-ylmethyl)phenylphosphine

摘要

The new heterofunctional phosphine ligand bis(2-oxazolin-2-ylmethyl)phenylphosphine (N, P, N) has been prepared and has allowed the synthesis of the ruthenium complexes fac-[RuCl_2(DMSO)(N, P, N)]1, fac-[RuCl_2(PPh_3)(N, P, N)] 2, [RuCl(#eta#~6-C_6H_6)(N, P, N)][O_3SCF_3] 3 and [Ru(#eta#~6-C_6H_6)(N, P, N)][O_3SCF_3]_2 4. When tridentate, as in 1, 2, and 4, this ligand co-ordinates in a facial-type mode. In complex 3, it acts as a P, N-chelate with a dangling oxazoline ring. The structures of the ligand, 2 centre dot CH_2Cl_2 centre dot 0.25C_6H_(14) and 3 have been determined by X-ray diffraction. Complexes 1-4 catalyse the transfer hydrogenation reaction between propan-2-ol and ketones. Only small differences in reactivity were observed between 3 and 4, despite the different ligand bonding mode in these complexes. For the best catalyst, 2, yields up to 97% were obtained and turnover frequencies may be as high as 112 000 h~(-1).