Functionalized periodic mesoporous organosilica: a highly enantioselective catalyst for the Michael addition of 1,3-dicarbonyl compounds to nitroalkenes.

A functionalized periodic mesoporous organosilica with incorporated chiral bis(cyclohexyldiamine)-based Ni(II) complexes within the silica framework was developed by the co-condensation of (1R,2R)-cyclohexyldiamine-derived silane and ethylene-bridge silane, followed by the complexation of NiBr(2) in the presence of (1R,2R)-N,N'-dibenzylcyclohexyldiamine. Structural characterization by XRD, nitrogen sorption, and TEM disclosed its orderly mesostructure, and FTIR and solid-state NMR spectroscopy demonstrated the incorporation of well-defined single-site bis(cyclohexyldiamine)-based Ni(II) active centers within periodic mesoporous organosilica. As a chiral heterogeneous catalyst, this functionalized periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in the asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroalkenes, comparable to those with homogeneous catalysts. In particular, this heterogeneous catalyst could be recovered easily and reused repeatedly up to nine times without obviously affecting its enantioselectivity, thus showing good potential for industrial applications.