A practical FeCl3/HCl photocatalyst for versatile aliphatic C–H functionalization

Abstract

The practical and diversified functionalization of ubiquitous C(sp 3 )–H bonds is an economically attractive yet chemically challenging approach to build molecular complexity from abundant chemical raw materials. Herein, we have identified a very robust and practical FeCl 3 /HCl photocatalytic system that enables greatly efficient C–H alkylation, oxidation, chlorination, fluorination, amination, alkynylation, and sulfonylation with total turnover number (TON) of up to 9,900. The aliphatic C–H activation is mediated by chlorine radical, in situ generated from a photoactive tetrahedral [Fe III Cl 4 ] − via ligand-to-metal charge transfer excitation, and the use of HCl as co-catalyst significantly improves the total TON by more than one order of magnitude. • Efficient and cheap photocatalyst generated from FeCl 3 and hydrochloric acid • Practical and diversified functionalization of aliphatic C–H bonds • Detailed mechanistic investigation for photoactive species The aliphatic C–H functionalization has been recognized as an ideal springboard to build molecular complexity from simple molecules with minimal manipulations. In recent years, photoinduced hydrogen atom transfer (HAT) catalysis has emerged as a powerful tool for aliphatic C–H activation by taming the light energy. There has been increasing interest in this prevailing research area, as witnessed by the blowout growth of efficient HAT photocatalysts. Here, we go a step further to report a practical and cheap FeCl 3 /HCl photocatalyst, allowing the diversified functionalization of numerous feedstock chemicals. Notably, the use of HCl as promotor can improve the total turnover number by more than one order of magnitude. Mechanistic investigations shed light on a photoactive tetrahedral [Fe III Cl 4 ] − species that is responsible for generating a chlorine radical via ligand-to-metal charge transfer excitation. The diversified functionalization of aliphatic C–H bonds has been readily established using a practical and economical FeCl 3 /HCl photocatalytic system, in which the use of HCl as promotor can improve the total turnover number by more than one order of magnitude. Mechanistic investigations suggest that this aliphatic C–H functionalization is mediated by a chlorine radical, generated from a photoactive tetrahedral [Fe III Cl 4 ] − species through ligand-to-metal charge transfer (LMCT) excitation.