Merging Chiral Diamine and Ni/SiO2 for Heterogeneous Asymmetric 1,4-Addition Reactions

The development of chiral solid catalysts using strategies different from conventional heterogenization methods is of great importance for efficient heterogeneous asymmetric catalysis. Herein, we report the preparation of a chiral solid catalyst, chiral diamine modified Ni/SiO2, for asymmetric Michael addition, a representative carbon-carbon bond-forming reaction. With dimethyl malonate and (E)-(2-nitrovinyl)benzene as model substrates, the Ni/SiO2 modified with chiral diamine affords 93% ee and an apparent turnover frequency of 18.1 h(-1), 3.6-fold that of the corresponding chiral Ni complexes. The experimental results demonstrate that the peripheral Ni sites in close contact with SiO2 support are likely to be the active sites, which are distinct from homogenous complexes. The continuous flow production of chiral compounds for more than 65 h was achieved by packing the solid catalysts in a fixed bed reactor with dimethyl malonate and (E)-(2-nitrovinyl)benzene as substrates.