Diaryl-pyrazinoporphyrins – Prospective photocatalysts for efficient sulfoxidation

Abstract

New promising photoactive functionalized pyrazinoporphyrins were prepared and preliminarily tested as homogeneous catalysts in the photooxidation of organic sulfides. An extremely low loading of the catalysts (10−3 mol%) allowed oxidation of thioanizole to the corresponding sulfoxide with the conversion of 98–100%, TON ca. 95060–98000 and TOF ca. 5941–6125, providing the selectivity of the corresponding sulfoxide formation of 97–98%. A survey of the meso-substituents of the porphyrin was performed allowing determination of optimal derivatives providing high catalytic activity together with sufficient stability and solubility under reaction conditions and along the synthetic pathway. The results obtained upon variation of the electronic nature of the substituents at the sulfur atom allowed to reveal promising prospective for further systematic application of pyrazinoporphyrin photosensitizers. The presence of the diethoxyphosphoryl- and methoxycarbonyl-substituents in the prepared compounds allows to consider them as prospective starting materials for further grafting to solid supports and thus as a platform for the development of heterogeneous photocatalysts.