Intermediacy of Copper(I) under Oxidative Conditions in the Aerobic Copper-Catalyzed Decarboxylative Thiolation of Benzoic Acids

Despite the growing importance of oxidative decarboxylative coupling (ODC) reactions, they often require silver salts to serve as both oxidant and decarboxylation mediator. The use of O2 in place of silver would be ideal, yet there are few examples of aerobic variants and they are not well understood mechanistically. Here, we disclose a mechanistic study of the Cu-catalyzed aerobic decarboxylative thiolation reaction, and propose a pathway that involves the intermediacy of Cu(I) species, even under these oxidizing conditions. Decarboxylation from a Cu(I) carboxylate appears to be turn-over-limiting. Cu(II) carboxylates are not competent intermediates, indicating an alternative role for O2. We propose that O2 is responsible for oxidizing a Cu(I) thiolate intermediate to release tightly bound thiolate ligands. To the best of our knowledge, this is the first example of a kinetic study of an ODC reaction and may have implications for the development of related Cu-catalyzed decarboxylation reactions.