Abstract
Designing metal-free catalysts for solar energy conversion is a long-standing challenge in semiconductor photoredox catalysis (SPC). With visible-light-responsive hexagonal boron carbon nitride (h-BCN) as a non-metal photocatalyst, this system affords C-H/N-H coupling products with broad substitution tolerance and high efficiency with molecular oxygen as the terminal oxidant. The catalyst ...
Abstract
Designing metal-free catalysts for solar energy conversion is a long-standing challenge in semiconductor photoredox catalysis (SPC). With visible-light-responsive hexagonal boron carbon nitride (h-BCN) as a non-metal photocatalyst, this system affords C-H/N-H coupling products with broad substitution tolerance and high efficiency with molecular oxygen as the terminal oxidant. The catalyst exhibits remarkable performance for the selective C-H functionalization of electron-rich arenes to C-N products (yields up to 95%) and good stability (6 recycles). Both nitrogen heteroarenes and amine salts are competent coupling nucleophiles. Mechanically, the reactive oxygen species are superoxide anion radical (O-2(-center dot)) and H2O2, which are proved by electron spin resonance (ESR) data, KI-starch, and control experiments. In addition, kinetic isotope effect (KIE) experiments indicate that C-H bond cleavage is not involved in the rate limiting step. This semiconductor-based photoredox system allows for C-H amination free of any metals, ligands, strong oxidants, and additives. It provides a complementary avenue to C-H functionalizations and enables synthetic applications efficiently in a sustainable manner.
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