Combining Transition Metal Catalysis with Radical Chemistry: Dramatic Acceleration of Palladium-Catalyzed C-H Arylation with Diaryliodonium Salts

This paper describes a photoredox palladium/iridium-catalyzed C?H arylation with diaryliodonium reagents. Details of the reaction optimization, substrate scope, and mechanism are presented along with a comparison to a related method in which aryldiazonium salts are used in place of diaryliodonium reagents. The unprecedentedly mild reaction conditions (25?degrees C in methanol), the requirement for light and a photocatalyst, the inhibitory effect of radical scavengers, and the observed chemoselectivity trends are all consistent with a radical-mediated mechanism for this transformation. This stands in contrast to the analogous thermal reaction with diaryliodonium reagents that is believed to proceed via an ionic 2e- pathway and requires a much higher reaction temperature (100?degrees C).