A Nickel‐Diamine/Mesoporous Silica Composite as a Heterogeneous Chiral Catalyst for Asymmetric 1,4‐Addition Reactions

A chiral composite material, derived from the deposition of a chiral nickel–diamine complex via wet impregnation to MCM‐41, was shown to be an efficient heterogeneous catalyst for asymmetric 1,4‐addition reactions of 1,3‐dicarbonyl compounds with nitroalkenes, and of nitromethane with alkylidenemalonates. It was discovered that MCM‐41 enhanced the reactivity and improved the stability of the chiral nickel complex that resides within the mesoporous material.     

Cooperative Catalysis of an Alcohol Dehydrogenase and Rhodium‐Modified Periodic Mesoporous Organosilica

The combined use of a metal‐complex catalyst and an enzyme is attractive, but typically results in mutual inactivation. A rhodium (Rh) complex immobilized in a bipyridine‐based periodic mesoporous organosilica (BPy‐PMO) shows high catalytic activity during transfer hydrogenation, even in the presence of bovine serum albumin (BSA), while a homogeneous Rh complex exhibits reduced activity due to direct interaction with BSA. The use of a smaller protein or an amino acid revealed a clear size‐sieving effect of the BPy‐PMO that protected the Rh catalyst from direct interactions. A combination of Rh‐immobilized BPy‐PMO and an enzyme (horse liver alcohol dehydrogenase; HLADH) promoted sequential reactions involving the transfer hydrogenation of NAD⁺ to give NADH followed by the asymmetric hydrogenation of 4‐phenyl‐2‐butanone with high enantioselectivity. The use of BPy‐PMO as a support for metal complexes could be applied to other systems consisting of a metal‐complex catalyst and an enzyme.