Selective Alcohol and Hydrocarbon oxidation using new C-Scorpionate Cu(II) and Fe(III) catalysts: Synthesis, activity, and Mechanistic Insights

The selective oxidation of C–H bonds and alcohols remains one of the central challenges in sustainable synthetic chemistry, as it often requires harsh conditions, including high temperatures and elevated pressures. Developing earth-abundant metal catalysts capable of high activity under mild, environmentally benign conditions is a critical research priority. The C-scorpionate pro-ligands, when combined with first-row transition metals, can act as homogeneous catalysts for several reactions, including the oxidation of cycloalkanes under mild conditions, prompting us to investigate the pro-ligand's versatility. Herein, we report the synthesis and catalytic evaluation of a novel series of C-scorpionate Cu(II) and Fe(III) complexes for the oxidation of toluene, benzyl alcohol, and 1-phenylethanol. The new complexes were fully characterized using several techniques, including IR, XRD, cyclic voltammetry, TGA, magnetic susceptibility, UV-Vis, XPS, and Mössbauer spectroscopy. Under optimized, environmentally friendly conditions, these complexes deliver outstanding performance: TOFs of 5488 h⁻¹ (Cu) and 4925 h⁻¹ (Fe) for secondary alcohol oxidation, and selectivity exceeding 90% for benzaldehyde in primary alcohol transformations. These results were obtained under mild conditions, with a low catalytic load, and over short reaction times. Using CW-EPR spin-trap spectroscopy, we identify the key radical intermediates that intervene in the catalytic cycle, providing mechanistic insight into the reaction pathway for the oxidation of toluene and benzyl alcohol.