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.