Regioselective cycloruthenation of N-(benzylidene)benzylamines: Enantiopure catalysts for transfer hydrogenation

Abstract

The reaction between N-(benzylidene)benzylamines (p-RC6H4CH=NCH2C6H5; R = Cl, H, NO2, F, OMe), [RuCl2(η6-p-cymene)]2 and potassium acetate has cleanly furnished the corresponding cycloruthenated complexes C1–C5. The process is completely regioselective, with the formation in all cases of the endo-derivative, independently of the substituent of the aromatic ring. The five-membered endo-metallacycles C6 and C7 can also be obtained from the enantiopure imines (RC)-p-RC6H4CH=NCHMeC10H7 (R = Cl, H, respectively) working under similar conditions. The crystal structures of the seven metallated compounds have been determined by X-ray diffraction. These complexes are active as catalyst precursors for the reduction of acetophenone and benzophenone by transfer hydrogenation. An enantiomeric excess of up to 77% at room temperature has been obtained with the complex C7 in the reduction of acetophenone.