Nanodiamond derived N-doped sp3@sp2 hybrid carbocatalysts for the aerobic oxidative synthesis of 2-substituted benzoxazoles

Abstract

Carbocatalysts, as a member of metal-free catalysts, have shown promising potentials in many catalytic transformations in the past few decades. Nitrogen doping has been identified as an effective way to tailor the properties of carbocatalysts and render their potential use for various applications. It is also important to fabricate unique surface compositions or properties for the N species to enhance their intrinsic catalytic activities. Hybrid sp3@sp2 nanocarbons, from this perspective, could enhance catalytic activity by tuning the electronic structure of the active sites. Herein, N-doped sp3@sp2 hybrids were prepared from nanodiamonds (NDs) and (NH4)2CO3 as starting N precursor to dope the NDs and tune their sp3/sp2. The N-doped sp3@sp2 hybrid nanocarbons were studied in the oxidative catalytic synthesis of a broad series of drug-related compounds (23 examples of 2-substituted benzoxazoles, benzothiazoles and benzimidazoles). These catalysts show high catalytic activity and reusability in mild conditions. Their performances are comparable to homogeneous/heterogeneous metal-based catalysts. The pyridinic N species determine the enhancement in the catalytic performance. The mechanistic results indicate that the N-doped sp3@sp2 hybrid activates oxygen molecules to form O2•- as reactive oxygen species, which abstracts the proton attached on the catalyst's surface. This study provides an attractive and useful methodology for applying ND-derived carbocatalysts to synthesise 2-substituted benzoxazoles and more complex drug targets.