Dual-Functional Rhodium Photocatalysts for Cofactor Regeneration and Enzymatic CO₂ Reduction

We report a series of Rh(III) complexes bearing N-phenyl-2-pyridinecarboxamide-based ligands that exhibit superior performance in the visible-light-driven photoregeneration of NADH without requiring external photosensitizers. These complexes demonstrate enhanced light absorption, extended visible-region spectral coverage, and significantly improved catalytic turnover compared to the conventional [(Cp*)Rh(bpy)Cl]+ complex. Among them, the para-trifluoromethyl-substituted complex displays the highest reactivity, achieving the fastest NADH regeneration rate under self-photosensitized conditions. Structural analysis reveals that catalytic performance correlates with Rh–Cl bond length, and DFT calculations support a structure–activity relationship tied to HOMO–LUMO gaps and Rh–H bond metrics. Notably, these Rh complexes exhibit negligible NADH photooxidation, unlike systems using eosin Y (EY), leading to higher net NADH yields in the absence of sensitizers. When coupled with formate dehydrogenase, the photoregeneration system enables selective enzymatic reduction of CO2 to formate with a turnover number of up to 42,000, demonstrating the viability of this dual-functional catalyst platform for light-driven biocatalytic CO2 valorization. This study establishes a foundation for designing minimalist and efficient cofactor regeneration systems for artificial photosynthesis and carbon capture technologies.