Porphyrin-Polyoxotungstate Molecular Hybrid as a Highly Efficient, Durable, Visible-Light-Responsive Photocatalyst for Aerobic Oxidation Reactions.

Abstract

Organic-polyoxometalate (POM) hybrids have recently attracted considerable interest because of their distinctive properties and wide-ranging applications. For the construction of organic-POM hybrids, porphyrins are promising building units owing to their optical properties and reactivity, including strong visible-light absorption and subsequent singlet-oxygen (1O2*) generation. However, the practical utilization of porphyrins as photocatalysts and photosensitizers is often hindered by their own degradation by 1O2*. Therefore, there is a substantial demand for the development of porphyrin-derived photocatalysts with both high efficiency and durability. Herein, we present a porphyrin-polyoxotungstate molecular hybrid featuring a face-to-face stacked porphyrin dimer (I) fastened by four lacunary polyoxotungstates. Hybrid I exhibited remarkable efficiency and durability in photocatalytic aerobic oxidation reactions, and the selective oxidation of various dienes, alkenes, sulfides, and amines proceeded using just 0.003 mol % of the catalyst. Mechanistic investigations suggested that the high activity of I stems from the efficient generation of 1O2*, resulting from the heavy-atom effect of POMs. Furthermore, despite its high efficiency in 1O2* generation compared to free porphyrins, I exhibited superior durability against 1O2*-induced degradation under photoirradiation.