Organic–inorganic hybridization boosts the catalytic performance of Mn-based catalysts in the aerobic oxidation of benzylic and allylic C–H bonds

Abstract

An unprecedented organic–inorganic hybrid material (BA-Ni₂Mg₂Mn) has been contrived using Ni₂Mg₂Mn layered double hydroxide (LDH) and benzoic acid as the precursors. The hybrid exhibited significantly higher catalytic activity than the precursor in the C(sp³)–H bonds oxidation via switching the reaction path of HAT (hydrogen atom transfer) for the Ni₂Mg₂Mn-LDH to PCET (proton-coupled electron transfer) process. The turnover frequency (TOF) value significantly boosted from 27 h⁻¹ for Ni₂Mg₂Mn-LDH to 882 h⁻¹ for the hybrid material in the aerobic oxidation of benzyl methyl ether, which exceeds most reported catalysts. The characterization suggested that metal cations in hybrid coordinated with carboxylic acid in a monodentate manner, which would elevate the positive charge of Mn³⁺ species and the surface basicity probably related to M–O^2– structure. These improved properties facilitated the electron transfer and the proton transfer during the PCET process, respectively, and were responsible for the boosting catalytic performance for the hybrid in the aerobic oxidation of C(sp³)–H bonds. Various substrates can be tolerated by the present catalytic system, allowing the efficient synthesis of some valuable molecules over an extremely convenient reaction system employing molecular oxygen as the sole oxidant.