Mixed hetero-/homogeneous TiO2/N-hydroxyimide photocatalysis in visible-light-induced controllable benzylic oxidation by molecular oxygen

Homogeneous and heterogeneous types of catalysis are frequently considered as separate disciplines or even opposed to each other. In the present work, a new type of mixed hetero-/homogeneous catalysis was demonstrated for the case of selective alkylarene oxidation by molecular oxygen. The proposed catalytic system consists of two widely available components: N-hydroxyphthalimide (NHPI, a homogeneous organocatalyst for free-radical chain reactions) and nanosized TiO2 (heterogeneous UV-active photoredox catalyst). The interaction of NHPI with TiO2 allows for a shift from UV to visible light photoredox activity and generation of phthalimide-N-oxyl (PINO) radicals that diffuse into the solution where NHPI/PINO-catalyzed free-radical chain reaction can proceed without the additional light input providing a fundamental increase in energy efficiency. The NHPI/TiO2 ratio controls the selectivity of oxidation affording preferential formation of hydroperoxide or ketone from alkylarene. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

The study demonstrates a new type of mixed heterogeneous/homogeneous catalysis for selective alkylarene oxidation by utilizing the interaction between NHPI and TiO2, leading to an increase in energy efficiency.