The visible-light-driven transfer hydrogenation of nicotinamide cofactors with a robust ruthenium complex photocatalyst

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2020-04, Vol.22 (7), p.2279-2287
• Main Authors: Dong, Wenjin, Tang, Jie, Zhao, Lijun, Chen, Fushan, Deng, Li, Xian, Mo
• Format: Article
• Language: English
• Subjects: Amino acids; Cofactors; Crystallography; Decarboxylation; Glutamate dehydrogenase; Glutamic acid; Green chemistry; Hydrogenation; Light effects; Nicotinamide; Photocatalysis; Photocatalysts; Regeneration; Ruthenium; Ruthenium compounds
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d0gc00331j

The highly efficient regeneration of nicotinamide cofactors has been successfully achieved with a quantum yield ( Φ ) of 7.9 × 10 −3 via photocatalytic transfer hydrogenation in the presence of the ruthenium complex Ru(tpy)(biq)Cl 2 (where tpy = 2,2′:6′,2′′-terpyridine and biq = 2,2′-bisquinoline). The photocatalytic system is not only highly efficient but also tolerant to amino acid residues. The combination of this photocatalyst with glutamate dehydrogenase enabled the controllable and efficient synthesis of l -glutamate to be realized. A mechanism involving light-induced ligand exchange, decarboxylation and hydride transfer has been proposed. Kinetic isotope experiments revealed that the decarboxylation of [Ru(tpy)(biq)HCOO] + to [Ru(tpy)(biq)H] + was the rate-determining step with a small apparent activation energy of 3.2 ± 0.4 kcal mol −1 . The hydricity of [Ru(tpy)(biq)H] + was estimated, via reaction equilibrium, to be 40 ± 3 kcal mol −1 . The highly efficient regeneration of nicotinamide cofactors has been successfully achieved via photocatalytic transfer hydrogenation using an amino acid-residue tolerant ruthenium complex.