Photochemistry of Polyoxometalates as Homogeneous Photocatalysts for Redox Reactions of Organic Molecules

Abstract

Photoexcitation of the oxygen to metal charge-transfer band for alkylammonium polyoxometalates of Mo and W allows the transfer of a hydrogen-bonded proton from alkylammonium to a bridging oxygen atom at an octahedral site of the polyoxoanion and the subsequent redox reaction with water to yield reduced polyoxoanion and OH. Photoreduced polyoxoanions which exhibit oxidation potentials more negative than the reduction potential of water, lead to hydrogen generation as a result of the reduction of proton coupled with oxidation to original polyoxoanions. The significance of the highly negative oxidation potential for the photoreduced polyoxoanions can be considered in connection with the photocatalytic evolution of hydrogen from a great variety of organic molecules and their net oxidation. The polyoxometalates constitute an interesting family of potential sensitizer and relay species because of their variety of compositions and structure. © 1985, The Society of Synthetic Organic Chemistry, Japan. All rights reserved.