Gary Samuel, Woolley Jack, Goia Sofia, Bloom Steven
Department of Medicinal Chemistry, University of Kansas Lawrence 66045 USA
Department of Physics, University of Warwick Coventry CV4 7AL UK.
Chem Sci. 2024 Jun 18;15(29):11444-11454. doi: 10.1039/d4sc03054k. eCollection 2024 Jul 24.
Molecular flavins are one of the most versatile photocatalysts. They can coordinate single and multiple electron transfer processes, gift hydrogen atoms, form reversible covalent linkages that support group transfer mechanisms, and impart photonic energy to ground state molecules, priming them for downstream reactions. But one mechanism that has not featured extensively is the ability of flavins to act as photoacids. Herein, we disclose our proof-of-concept studies showing that electrophotochemistry can transform fully oxidized flavin quinones to super-oxidized flavinium photoacids that successfully guide proton-transfer and deliver acid-catalyzed products. We also show that these species can adopt a second mechanism wherein they react with water to release hydroxyl radicals that facilitate hydrogen-atom abstraction and spC-H functionalization protocols. Together, this unprecedented bimodal reactivity enables electro-generated flavinium salts to affect synthetic chemistries previously unknown to flavins, greatly expanding their versatility as catalysts.
分子黄素是用途最广泛的光催化剂之一。它们可以协调单电子和多电子转移过程、提供氢原子、形成支持基团转移机制的可逆共价键，并将光子能量赋予基态分子，使其为下游反应做好准备。但黄素作为光酸发挥作用这一机制尚未得到广泛研究。在此，我们披露了我们的概念验证研究，结果表明，光电化学可以将完全氧化的黄素醌转化为超氧化的黄素鎓光酸，成功引导质子转移并产生酸催化产物。我们还表明，这些物质可以采用第二种机制，即它们与水反应释放羟基自由基，促进氢原子提取和spC-H官能化反应。这种前所未有的双峰反应性使电生成的黄素鎓盐能够影响黄素以前未知的合成化学，极大地扩展了它们作为催化剂的用途。
