Co-function Mechanisms of Chlorine and Alkoxy Radicals in Cerium-Catalyzed C-H Functionalization of Alkane Mediated by Visible Light

Identificationof radical intermediates for the catalytic functionalizationof alkanes offers a number of unique challenges and has recently raiseda controversial issue concerning the subtle role of chlorine versusalkoxy radicals in cerium photocatalysis. This study is an attemptto settle the controversy within the theoretical frameworks of Marcuselectron transfer and transition state theory. Co-function mechanismswere proposed together with a scheme of kinetic evaluations to accountfor ternary dynamic competition among photolysis, back electron transfer,and hydrogen atom transfer (HAT). Cl & BULL;-based HAT has been provento initially control the early dynamics of the photocatalytic transformationon the picosecond to nanosecond time scale, which is subsequentlytaken over by a postnanosecond event of alkoxy radical-mediated HAT.The theoretical models developed herein provide a uniform understandingof the continuous time dynamics of photogenerated radicals to addresssome paradoxical arguments in lanthanide photocatalysis.

Automated summary

This study aims to settle the controversy regarding the role of chlorine versus alkoxy radicals in cerium photocatalysis by employing the theoretical frameworks of Marcus electron transfer and transition state theory. Co-function mechanisms and kinetic evaluations are proposed to explain the ternary dynamic competition among photolysis, back electron transfer, and hydrogen atom transfer (HAT). It is discovered that Cl·-based HAT initially controls the early dynamics of the photocatalytic transformation on the picosecond to nanosecond time scale, which is then taken over by alkoxy radical-mediated HAT in a postnanosecond event. The developed theoretical models offer a coherent understanding of the continuous time dynamics of photogenerated radicals in lanthanide photocatalysis and help address paradoxical arguments.