Efficient Nicotinamide Adenine Dinucleotide Regeneration with a Rhodium–Carbene Catalyst and Isolation of a Hydride Intermediate
Vinothkumar Ganesan, Jennifer Juhyun Kim, Jeongcheol Shin, Kiyoung Park, Sungho Yoon
Abstract
Regeneration of nicotinamide adenine dinucleotide (NADH) has been the primary interest in the field of enzymatic transformation, especially associating oxidoreductases given the stoichiometric consumption. The synthesized carbene-ligated rhodium complex [(η5-Cp*)Rh(MDI)Cl]+ [Cp* = pentamethylcyclopentadienyl; MDI = 1,1′-methylenebis(3,3′-dimethylimidazolium)] acts as an exceptional catalyst in the reduction of NAD+ to NADH with a turnover frequency of 1730 h–1, which is over twice that of the higher catalytic activity of the commercially available catalyst [Cp*Rh(bpy)Cl]+ (bpy = 2,2'-bipyridine). Offsetting the contentious atmosphere currently taking place over the specific intermediate of the NADH regeneration, this study presents pivotal evidence of a metal hydride intermediate with a bis(carbene) ligand: a stable form of the rhodium hydride intermediate, [(η5-Cp*)Rh(MDI)H]+, was isolated and fully characterized. This enables thorough insight into the possible mechanism and exact intermediate structure in the NAD+ reduction process.