5 years ago

Photocatalytic Aerobic Thiol Oxidation with a Self-Sensitized Tellurorhodamine Chromophore

Photocatalytic Aerobic Thiol Oxidation with a Self-Sensitized Tellurorhodamine Chromophore
Mathew W. Eskew, Michael R. Detty, Haley E. Irving, Kellie S. Davies, Luke V. Lutkus, Theresa M. McCormick, James E. Lohman, Jacqueline E. Hill
Aerobic oxidation of thiols to disulfides was achieved photocatalytically using a tellurorhodamine chromophore (9-mesityl-3,6-bis(dimethylamino)telluroxanthylium hexafluorophosphate) as both the sensitizer and catalyst. The proposed mechanism, supported experimentally and computationally with DFT, involves the formation of a tellurorhodamine telluroxide from reaction with water and singlet oxygen generated by irradiation of the tellurorhodamine. The oxidation to the telluroxide is accompanied by the formation of hydrogen peroxide. The telluroxide oxidizes thiols to regenerate the tellurorhodamine and the disulfide plus water. Mechanistically, DFT suggests adding two thiols to the telluroxide with the loss of H2O to give a trigonal-bipyramidal Te(IV), which undergoes concerted loss of disulfide to regenerate 1. Oxidation of thiophenol and 2-naphthalenethiol was complete after 2 h of irradiation with visible light under atmospheric conditions. Oxidation of the electron-poor 2,6-dichlorothiophenol, the sterically bulky tert-butylmercaptan, and aliphatic dodecanethiol was slower. The two aliphatic thiols displayed competing catalyst degradation. The corresponding selenorhodamine chromophore (9-mesityl-3,6-bis(dimethylamino)selenoxanthylium hexafluorophosphate) does not form the corresponding selenoxide under similar conditions and photooxidizes thiophenol and 2-naphthalenethiol much more slowly (≤6% conversion after 2–3 h).

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00166

DOI: 10.1021/acs.organomet.7b00166

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