Studies on Inert-Alkane Oxidation Systems with Reactive-Oxygen Transition-Metal Complexes

Abstract

This study explores the selective oxidation of inert hydrocarbons employing transition-metal complexes bearing reactive oxygen ligand, inspired by metalloenzyme mechanisms. We developed oxidation systems enabling hydroxylation of unactivated alkanes and arenes under mild conditions, focusing on direct observation of catalytic active species. Using iron-porphyrin complexes, we established a system stabilizing the Compound I model species even near room temperature, overcoming previous limitations from its extreme reactivity. This allowed for quantitative analysis of C–H hydroxylation, revealing new structure–reactivity correlations, including the roles of axial ligand of Compound I and bond “hardness” of the substrate. We also designed redox-active ligand frameworks to facilitate alkane oxidation through a concerted mechanism, and fluorocarbon-phase catalysts that selectively hydroxylate alkanes while suppressing overoxidation of alcohols via product-phase separation. In parallel, we investigated arene hydroxylation catalyzed by nickel complexes supported by multidentate amine ligands, achieving high selectivity and proposing a di(μ-oxido)dinickel(III) complex as the active intermediate. Overall, this research provides new insights into hydrocarbon activation via well-defined high-valent metal–oxido species, with implications for catalyst design.