Supremely high turnover numbers with a simple porphyrin photosensitizer: Kinetic and mechanistic insights into the oxidation of sulfides with singlet oxygen

The evaluation of the porphyrin-sensitized photocatalytic sulfoxidation mechanism with kinetic studies and DFT calculations is reported. The precise evaluation of the factors, determining the observed efficiency of the photocatalytic process, namely the photostability of the sensitizer, its loading, origin of the solvent, was performed. The revealed insights into the reaction mechanism allowed the development of the photooxidation protocol exceeding the turnover number (TON) values of typical porphyrin sensitizers by ca. two orders of magnitude reaching values up to830000 using a simple tetrapyrrolic sensitizer (5,10,15,20-tetraphenylporphyrin, TPP). The scope of the developed protocol is proved by preparation of a series of sulfoxides bearing substituents of different electronic nature. The applicability of the developed protocol is a gram-scale sulfoxidation which was also successfully demonstrated.