Catalytic hydrogenation under H2 and transfer hydrogenation of imines by secondary alcohols with hydridoruthenium complexes bearing PMe 3 and PPh3 ligands have been examined. A cationic hydridoruthenium complex, cis-[RuH-(NH3)(PMe3) 4]PF6 (2), derived from cis-[RuH2(PMe 3)4] (1) and NH4PF6, showed higher catalytic activity for H2-hydrogenation of N-benzylideneaniline than neutral complexes such as 1 and cis- [RuClH(PMe3)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 (CH3) 2CHOD. On the basis of the experimental results the mechanisms of the H2-hydrogenation and transfer hydrogenation are discussed.
ASJC Scopus subject areas
- 化学 (全般)