Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.
Dalton Trans. 2021 Jan 14;50(2):675-680. doi: 10.1039/d0dt04004e. Epub 2020 Dec 17.
The sequential transfer of an electron, a proton and an electron in a hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) and its analogues has never been separated well. In addition, the effect of acids on hydride transfer from an NADH analogue to a metal-superoxo species has yet to be reported. We report herein the first example of an acid-promoted hydride transfer from an NADH analogue, 10-methyl-9,10-dihydroacridine (AcrH), to a Cr(iii)-superoxo complex, [(TMC)Cr(O)], in the presence of HOTf in MeCN at 233 K. The acid-promoted hydride transfer from AcrH to [(TMC)Cr(O)] occurs via a proton-coupled hydrogen atom transfer from AcrH to [(TMC)Cr(O)] to produce a radical cation (AcrH˙) with an inverse deuterium isotope effect (KIE) of 0.93(5). AcrH˙ decayed via a proton transfer from AcrH˙ to AcrH with a KIE of 2.0(1), followed by the reaction of 10-methylacridinyl radical (AcrH˙) with [(TMC)Cr(HO)] to produce a 10-methylacridinium ion (AcrH) and [(TMC)Cr]. This work provides valuable insights into the mechanism of hydride transfer of NADH analogues by metal-superoxo intermediates, such as the switchover of the reaction mechanism from a one-step to a separated multi-step pathway in the presence of an acid.
从二氢烟酰胺腺嘌呤二核苷酸（NADH）及其类似物中的氢化物转移中，电子、质子和电子的连续转移从未得到很好的分离。此外，还没有报道过酸对NADH 类似物向金属过氧物种的氢化物转移的影响。我们在此报告了首例在酸存在下，在 MeCN 中于 233 K 时，从 NADH 类似物 10-甲基-9,10-二氢吖啶（AcrH）向 Cr(iii)-过氧配合物[(TMC)Cr(O)]的酸促进氢化物转移的实例。在[(TMC)Cr(O)]存在下，AcrH 向[(TMC)Cr(O)]的酸促进氢化物转移通过 AcrH 向[(TMC)Cr(O)]的质子偶联氢原子转移发生，产生带有反氘同位素效应（KIE）为 0.93(5)的自由基阳离子（AcrH˙）。AcrH˙ 通过 AcrH˙向 AcrH 的质子转移衰减，KIE 为 2.0(1)，随后 10-甲基吖啶基自由基（AcrH˙）与[(TMC)Cr(HO)]反应生成 10-甲基吖啶鎓离子（AcrH）和[(TMC)Cr]。这项工作为金属过氧中间体（如在酸存在下从一步反应到分离的多步途径的反应机制的转换）中 NADH 类似物的氢化物转移机制提供了有价值的见解。
