Rh-Functionalized Donor−π–Acceptor Covalent Organic Framework for Efficient Photocatalytic Nicotinamide Cofactor Regeneration

A nicotinamide adenine dinucleotide phosphate (NADPH)-mediated photoenzyme-coupled catalytic system is an attractive and green strategy for chemical conversion. However, artificial photocatalytic NADPH regeneration with low activity and selectivity has posed a challenge when it is coupled with enzyme catalysis. Therefore, we developed a strategy to prepare an "all-in-one" photocatalyst (Rh-sp2c-COF) by immobilizing an electron mediator ([Cp*Rh(bpy)(H2O)]2+) in a covalent organic framework (COF) with a donor−π–acceptor structure for efficient photocatalytic NADPH regeneration. The immobilized [Cp*Rh(bpy)(H2O)]2+ not only achieves specific regeneration of 1,4-NADPH but also improves the efficiency of electron transfer and utilization by constructing intramolecular electron transfer channels and electron buffer tanks. In addition, the donor−π–acceptor structure expands the range of light absorption and promotes effective carrier separation and directional transfer. The turnover frequency of NADPH regeneration by Rh-sp2c-COF reaches 2.17 mmol·gCOF–1·h–1, which is 3.28, 1.99, and 4.5 times higher than those of sp2c-COF, sp2c-COF + free [Cp*Rh(bpy)(H2O)]2+, and imine-COF, respectively. Finally, Rh-sp2c-COF coupled with ene reductase achieves efficient asymmetric hydrogenation of C═C. This work provides an approach for accurate predesign of photocatalysts to achieve efficient conversion and utilization of solar energy.