Overcoming Photochemical Limitations in Metallaphotoredox Catalysis: Red-Light-Driven C-N Cross-Coupling

Abstract

Aryl amination is an essential transformation for medicinal, process, and materials chemistry. In addition to classic Buchwald-Hartwig amination conditions, blue-light-driven metallaphotoredox catalysis has emerged as a valuable tool for C-N cross-coupling. However, blue light suffers from low penetration through reaction media, limiting its scalability for industrial purposes. In addition, blue light enhances unwanted side-product formation in metallaphotoredox catalysis, namely hydrodehalogenation. Low-energy light, such as deep red (DR) or near-infrared (NIR), offers a solution to this problem as it can provide enhanced penetration through reaction media as compared to higher-energy wavelengths. Herein, we show that low-energy light can also enhance the desired reactivity in metallaphotoredox catalysis by suppressing unwanted hydrodehalogenation. We hypothesize that the reduced side product is formed by direct photolysis of the aryl-nickel bond by the high-energy light, leading to the generation of aryl radicals. Using deep-red or near-infrared light and an osmium photocatalyst, we demonstrate an enhanced scope of (hetero)aryl bromides and amine-based nucleophiles with minimal formation of hydrodehalogenation byproducts.