Evolution of manganese low-energy photoredox catalysis from high-energy visible light photocatalysis

Reducing the energy input of light in photocatalytic reactions is desirable yet challenging, as modifying the light-absorbing or catalytic properties of a photocatalyst typically requires tedious preparation, resulting in a lengthy development process. Here, we overcome this limitation by achieving manganese-based low-energy photoredox catalysis through the in-situ assembly of simple Mn salts with inexpensive coordinating chemicals, thereby bypassing the need for complex pre-preparation. Assembling Mn(acac)2, 2,2’-bipyridine-6,6’-diamine, and TMSN3 in-situ forms a visible-light-absorbing system that, upon blue-light irradiation, generates azido radicals to drive an anti-Markovnikov hydroazidation of unactivated alkenes with H2O as the hydrogen source. Building on this assembly strategy, the combination of Mn(acac)3 and TMSN3 in CH3CN/HFIP yields a system with a light-absorption range extended to 850 nm; this feature is further leveraged to unlock the selective aerobic hydroxyazidation of alkenes in a single step. These findings pave the way for the development of in-situ-assembled, 3 d metal-based low-energy photochemistry. Modifying the light-absorbing or catalytic properties of a photocatalyst typically requires tedious preparation, resulting in a lengthy development process. Here, the authors address this limitation by achieving manganese-based low-energy photoredox catalysis through the in-situ assembly of simple Mn salts with inexpensive coordinating chemicals.