Exploiting mesoporous silica matrixes for aqueous asymmetric transfer hydrogenation: morphology and surface chemistry dominate catalytic performance

Three typical mesoporous silica materials functionalized with chiral N-sulfonylated diamine-based organorhodium complex are developed and their aqueous asymmetric transfer hydrogenations of aromatic ketones are investigated. Structural characterizations of XRD spectra, nitrogen sorption and TEM images disclose their orderly mesostructures, and solid-state NMR spectra demonstrate their well-defined single-site chiral organorhodium active centers incorporated within silicate networks. As heterogeneous chiral catalysts, these functionalized silicas exhibit obvious differences in both catalytic activities and enantioselective performances in aqueous asymmetric transfer hydrogenation. As expected, the special hydrophobicity of periodic mesoporous organorhodium silicate matrix significantly increases reaction rate while the open mesostructural morphology of nanosphere-based silicate matrix can maintain its original chiral microenvironment. In particular, novel immobilized strategy and unique nanocages of mesoporous SBA-16 matrix realize the transfer from heterogeneous catalysis to homogeneous catalysis, presenting a highly catalytic and recyclable efficiency.