Arylthianthrenium Salts\nfor Triplet Energy Transfer\nCatalysis

Sigma bond cleavage\nthrough electronically excited states\nallows\nsynthetically useful transformations with two radical species. Direct\nexcitation of simple aryl halides to form both aryl and halogen radicals\nnecessitates UV-C light, so undesired side reactions are often observed\nand specific equipment is required. Moreover, only aryl halides with\nextended π systems and comparatively low triplet energy are\napplicable to synthetically useful energy transfer catalysis. Here\nwe show the conceptual advantages of arylthianthrenium salts (ArTTs)\nfor energy transfer catalysis with high energy efficiency compared\nto conventional aryl (pseudo)halides and their utility in arylation\nreactions of ethylene. The fundamental advance is enabled by the low\ntriplet energy of ArTTs that may originate in large part from the\nelectronic interplay between the distinct sulfur atoms in the tricyclic\nthianthrene scaffold, which is not accessible in either simple (pseudo)halides\nor other conventional sulfonium salts.