Merging Transition-Metal Catalysis with Photoredox Catalysis: An Environmentally Friendly Strategy for C–H Functionalization

Abstract

Transition-metal-catalyzed C–H functionalization is already a useful tool in organic synthesis, whilst the rapid development of photoredox catalysis provides new pathways for C–H functionalization with high selectivity and efficiency under mild reaction conditions. In this review, recent advances in C–H functionalization through merging transition­-metal catalysis with photoredox catalysis are discussed.1 Introduction2 Merging Nickel Catalysis with Photoredox Catalysis3 Merging Palladium Catalysis with Photoredox Catalysis4 Merging Cobalt Catalysis with Photoredox Catalysis5 Merging Photoredox Catalysis with Other Transition-Metal Catalysis­6 Conclusions

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

“…On the other hand, photoredox catalysis has been mainly employed for electron-transfer reactions and, remarkably, few examples have been reported in which the photoredox process modifies the oxidation state of a catalyst [55,56]. Subsequently, C-H activation protocols benefiting from mild photocatalytic reoxidation have spread rapidly [60][61][62]. In such a case, a photocatalyst (PC) is introduced in the reaction media in order to transfer electrons from the low-valent metal complex formed in situ after reductive elimination of the product (Figure 4, right).…”

“…Accordingly, numerous unprecedented reactions involving photoredox catalysis in synergy with other activation modes including Brønsted/Lewis acid catalysis, organocatalysis, enzymatic biocatalysis, or electrocatalysis, have been achieved recently [53][54][55][56][57][58]. In addition, various transformations merging photoredox catalysis with transition-metal catalysis have been disclosed [59][60][61][62][63][64][65]. Among these different strategies, visible-light photoredox catalysis combined with nickel catalysis is undoubtedly the most thoroughly investigated approach and consequently, the most widely described in the literature [66,67].…”

Recent Advances on Synthetic Methodology Merging C–H Functionalization and C–C Cleavage

“…The past twenty years have witnessed a great evolution in the approach to perform the functionalization of C–H bonds, enhancing its applicability [ 8 ]. Nowadays, there is a growing interest to extend the frontiers of the C–H functionalization field through its merging with other aspects of synthesis, for instance electrochemical [ 9 , 10 , 11 ]; and photochemical processes [ 12 , 13 ], cascade reactions [ 14 , 15 ], or functionalization of remote positions [ 16 , 17 , 18 , 19 ], among others. Parallel to the research on C–H functionalization, the topic of C–C bond cleavage has experienced an exponential development in recent times [ 20 , 21 , 22 , 23 , 24 , 25 ].…”

Metal-supported and -assisted stereoselective cooperative photoredox catalysis

“…Therefore they depend on each other for the formation of new bonds. Recently, some reviews covering the aspects of metals in photocatalysis [22][23][24][25][26][27][28] and another review on enantioselective photoinduced organocatalysis 29 were published. We ask the reader to refer to these reviews for a comprehensive survey regarding dual catalysis via photoirradiation.…”