Modular and Selective Arylation of Aryl Germanes (C-GeEt3 ) over C-Bpin, C-SiR3 and Halogens Enabled by Light-Activated Gold Catalysis.

Selective C sp 2 -C sp 2 couplings are powerful strategies for the rapid and programmable construction of bi- or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd-catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd0 /PdII catalysis) in the presence of the valuable functionalities C-BPin, C-SiMe3 , C-I, C-Br, C-Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C-Ge with aryl diazonium salts. Contrary to previous light-/gold-catalyzed couplings of Ar-N2 + , which were specialized in Ar-N2 + scope, we present conditions to efficiently couple electron-rich, electron-poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron-poor Ar-N2 + salts are readily activated by gold under blue-light irradiation, there is a competing dissociative deactivation pathway for excited electron-rich Ar-N2 + , which requires an alternative photo-redox approach to enable productive couplings.