Center of Basic Molecular Science (CBMS), Department of Chemistry, Tsinghua University, Beijing, China.
School of Chemistry and Chemical Engineering, Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing, China.
College of Chemistry and Institute of Green Catalysis, Zhengzhou University, Zhengzhou, Henan, China.
Structure, reactivity and catalytic properties of manganese-hydride amidate complexes
The high efficiency of widely applied Noyori-type hydrogenation catalysts arises from the N–H moiety coordinated to a metal centre, which stabilizes rate-determining transition states through hydrogen-bonding interactions. It was proposed that a higher efficiency could be achieved by substituting an N–M′ group (M′ = alkali metals) for the N–H moiety using a large excess of metal alkoxides (M′OR); however, such a metal-hydride amidate intermediate has not yet been isolated. Here we present the synthesis, isolation and reactivity of a metal-hydride amidate complex (HMn–NLi). Kinetic studies show that the rate of hydride transfer from HMn–NLi to a ketone is 24-fold higher than that of the corresponding amino metal-hydride complex (HMn–NH). Moreover, the hydrogenation of N-alkyl-substituted aldimines was realized using HMn–NLi as the active catalyst, whereas HMn–NH is much less effective. These results highlight the superiority of M/NM′ bifunctional catalysis over the classic M/NH bifunctional catalysis for hydrogenation reactions.