Engineering and Sizing Nanoreactors To Confine Metal Complexes for Enhanced Catalytic Performance

Abstract

Homogeneous metal complexes often display superior activity and selectivity in catalysis of chemical transformations. Heterogenization of these complexes by immobilization on solid supports has been used to facilitate recovery, but this is often associated with a decrease in catalytic performance. We here describe a novel approach of sizing and engineering the cavity structure of nanoporous materials as "nanoreactors" to assemble metal complexes by the "ship-in-the-bottle" synthesis to combine the best of homogeneous and heterogeneous catalysts. Catalysis occurred by free metal complexes in confined liquid in these nanoreactors, while the catalysts were recyclable as being heterogeneous at the macroscopic scale. Subnanometer tailoring of window sizes (0.5-3.7 nm) of the cavities (16-22 nm) allowed control over loading (6-70 mg-metal complex/g-support) and a high turnover frequency (40-600 h(-1)) for the hydrolytic kinetic resolution of 1,2-epoxyhexane. Most importantly, the 'heterogeneous homogeneous catalysts' showed enhanced thermal stability and were stable upon reuse approaching excellent turnover numbers of 100,000. We showed this that engineering and sizing of nanoreactors is a powerful approach to control performance of confined catalysts, and method is generally applicable in host guest catalysis.