Catalytic Behavior of Cationic Hydridoruthenium(II) Complex, [RuH(NH3)(PMe3)4]+, in H2-Hydrogenation and Transfer Hydrogenation of Imines

Catalytic hydrogenation under H 2 and transfer hydrogenation of imines by secondary alcohols with hydridoruthenium complexes bearing PMe 3 and PPh 3 ligands have been examined. A cationic hydridoruthenium complex, cis-[RuH-(NH 3 )(PMe 3 ) 4 ]PF 6 (2), derived from cis-[RuH 2 (PMe 3 ) 4 ] (1) and NH 4 PF 6 , showed higher catalytic activity for H 2 -hydrogenation of N-benzylideneaniline than neutral complexes such as 1 and cis-[RuClH(PMe 3 ) 4 ] (6). The effectiveness of cationic hydridoruthenium species for the catalytic H 2 -hydrogenation of benzylideneaniline was also demonstrated by a marked increase in the yield of N-benzylaniline on treatment of 6 with AgPF 6 . The cationic complex 2 was applicable to catalytic transfer hydrogenation of imines with secondary alcohols even in the absence of a base. Isotope labeling experiments using deuterated alcohols revealed that the hydrogen atom bound to the α-carbon of the donor alcohol was transferred exclusively to the imine carbon and alcoholic OD was transferred to the imine nitrogen. A rapid exchange between the alcoholic proton and the hydrido ligand of 2 was also confirmed by NMR investigation using (CH 3 ) 2 CHOD. On the basis of the experimental results the mechanisms of the H 2 -hydrogenation and transfer hydrogenation are discussed.