Synthesis of boron doped polymeric carbon nitride solids and their use as metal-free catalysts for aliphatic C–H bond oxidation

Abstract

Oxidation of hydrocarbons with clean oxidants is a crucial process for the development of products ranging from commodity chemicals to speciality pharmaceuticals. While selective oxidation is commonplace in nature and mainly occurs through a broad variety of cytochrome P450 enzymes, the synthetic catalysts that have been identified so far are relatively inactive with aliphatic C–H bonds. We present here a promising strategy for modifying polymeric graphitic carbon nitride by replacing the carbon atoms in the “melon” network using boron. ¹¹B solid-state MAS NMR and XPS spectral studies confirmed the incorporation of the boron atoms in the polymeric g-C₃N₄ as well as the degree of doping, while X-ray diffraction and IR indicated that the characteristic structural properties of polymeric g-C₃N₄, such as the original graphitic structure, and the C–N heterocycle units were essentially retained. The boron-doped polymeric carbon nitride shows promising catalytic activity and high selectivity (≥87%) in the oxidation of benzylic aromatics. The use of this metal-free, organic, semiconducting polymer as an oxidation catalyst and H₂O₂ or O₂ as oxidants makes the reactions interesting from both an economic and environmental point of view. It is also hoped that our findings will stimulate further investigation and will open new possibilities to form hybrid carbon nitride materials with new and probably exciting applications.