Facile synthesis of versatile bifunctional photo-organocatalytic metal-organic frameworks for α-alkylation of aldehydes and cross-dehydrogenative coupling reactions

The development of highly efficient and recyclable bifunctional photoredox catalysts is extremely promising for organic synthesis. In this study, a novel kind of bifunctional metal-organic framework (MOF) based catalysts were prepared through the in-situ incorporation of the L -proline moiety into the MOF network and followed by the anchoring of dye molecules via a solvothermal process. These catalysts exhibited versatile catalytic activity in the visible light triggered α -alkylation of aldehydes and cross-dehydrogenative coupling reactions between N -aryl tetrahydroquinolines and ketones. The control experiments revealed enhanced synergy existed between the two kinds of catalytic active centers confined in the porous framework, resulting in significantly enhanced catalytic activities while maintaining comparable enantioselectivities to the corresponding homogeneous catalytic systems. Furthermore, the bifunctional catalysts showed high stability and reusability over five consecutive cycles with only a slight decrease in activity. Based on the experimental results, a plausible reaction mechanism over the present bifunctional catalyst was proposed.