Aqueous-phase NADH regeneration using Rh(N-heterocyclic carbene) catalyst with enhanced hydride kinetics

초록

Nicotinamide adenine dinucleotide (NADH) serves as a two-electron and one-proton donor in redox biocatalysis, yet its high cost and stoichiometric consumption limit large-scale applications. A [Cp*Rh(N<^>C)Cl]+ complex featuring a mono(NHC-pyridyl) chelating ligand has been developed for the efficient regeneration of NADH in aqueous media. Kinetic investigations demonstrate that this Rh(iii) complex forms the key Rh-H intermediate over ten times faster than its bipyridine-based analogs, owing to the favorable electronic and steric effects of the NHC ligand. Mechanistic analysis indicates that the Rh-H species, rather than Cp*-H, acts as the primary reducing agent, facilitating regioselective conversion of NAD+ to biologically active 1,4-NADH. Under optimized conditions, the catalyst achieves a turnover frequency (TOF) of 7000 h-1, marking the highest reported activity among Rh-based systems for chemical NADH regeneration in aqueous medium. These results highlight a new structure-reactivity relationship in hydride-transfer catalysis and provide a design blueprint for high-performance regeneration systems in biocatalytic and green chemical applications.

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