Spirobifluorene-based conjugated microporous polymer embedded with N-hydroxyphthalimide as a synergistic photocatalyst for selective solvent-dependent aerobic oxidations

Abstract

The ideal catalytic oxidation system that uses the most environmentally benign reactants, such as molecular oxygen and natural light, and features sustainable heterogeneous characteristics, although long sought, has hardly been achieved. Herein, a spirobifluorene-based conjugated microporous polymer (CMP) covalently embedded with N-hydroxyphthalimide (NHPI) as a phthalimido N-oxyl (PINO) radical precursor was designed and synthesized. The as-synthesized porous CMP-NHPI leverages the spirobifluorene-based CMP as an exquisite photoredox platform to activate molecular oxygen for generating reactive oxygen species (ROS) and synergistically convert the embedded NHPI to an active PINO radical, thus establishing a fully green catalytic system. In particular, under visible light irradiation and air at ambient temperature, various primary aromatic alcohols can be highly selectively oxidized to their corresponding aldehydes or acids by switching the reaction solvent from acetonitrile to water. Control experiments and mechanistic studies reveal that the regulation of ROS in different solvents is responsible for the specific solvent-dependent oxidations.