Facile Fe-Based Hybrid Enables the Efficient Production of <i>N</i>-Oxyl Radical for the Aerobic Oxidation of Alkylarenes under Solvent-Free Conditions

A facile Fe-based organic–inorganic hybrid material (BA-Mg2Fe) has been fabricated by using Mg2Fe layered double hydroxide (LDH) and benzoic acid (BA) as the precursors. The hybrid demonstrated significantly higher catalytic performance than the precursor in activating the N-hydroxyphthalimide molecule to the phthalimide N-oxyl species, predominantly by switching the hydrogen atom transfer to the proton-coupled electron transfer process. The enhancement of activity can be mainly attributed to the elevation of the positive charge of Fe3+, which facilitates electron transfer, and the increased amount of the surface medium strong basic sites, which accelerates proton transfer. In addition, the hybrid BA-Mg2Fe catalyst coated with organic molecules had lower polarity and better compatibility with oxygen molecules and substrates compared to the precursor Mg2Fe-LDH. As a result, the conversion of ethylbenzene reached 74.8% with an excellent 96.1% selectivity of acetophenone in the aerobic oxidation of ethylbenzene under solvent-free conditions; the apparent activation energy (Ea) decreased from 86.9 kJ/mol for Mg2Fe-LDH to 48.3 kJ/mol for BA-Mg2Fe, and the turnover frequency value boosted from 7.7 to 246.0 h–1. The catalytic system also possesses the advantages of catalytical and structural stability, as well as tolerance of various substrates.