Viologens for Coenzymes of Biocatalysts with the Function of CO₂ Reduction and Utilization

In this review, the recent studies on 1) the visible-light-induced reduction of CO2 to formic acid catalyzed by formate dehydrogenase (FDH) via the reduction of a 4,4′- or 2,2′-bipyridinium salt (BP2+) by a photosensitizer, 2) the electrochemical properties of BP2+, and 3) the enzymatic kinetic properties of the interaction between the reduced forms of BP2+ and FDH are reviewed. Moreover, visible-light-induced biocatalytic C–C bond formation using CO2 as a feedstock via photoreduction of the phenylviologen derivative is introduced.