Flash Communication: Isolation and Interconversion of a Coenzyme–NAD⁺/NADH Model Pair Based on Regioselective Hydrogenation of the Noninnocent Ligand on Ru Complexes

Constructing an energy system inspired by natural processes to harness chemical energy is key to creating an environmentally benign energy system. A critical yet challenging research area involves the design and development of model compounds that mimic the function of the active site of the coenzyme–nicotinamide adenine dinucleotide (NAD) system. In this study, we synthesized a Ru complex system containing a molecular framework similar to the active site of that system. The molecular structures of the oxidized (NAD+-type complex) and reduced (NADH-type complex) forms were elucidated through spectroscopic measurements and X-ray crystallographic analyses. The hydrogenation of the NAD+-type complex was achieved using molecular hydrogen generated via the water–gas shift reaction of carbon monoxide. Conversely, the NADH-type complex was quantitatively converted to the corresponding NAD+-type complex upon visible-light irradiation. Further, we demonstrated the interconversion between the NAD+- and NADH-type complexes. This Ru-based complex system served as a robust model for the coenzyme–NAD system. In addition, the complex system showed potential as a new “hydrogen carrier”, capable of releasing hydrogen gas under mild conditions.