Oxidant-free Au(I)/Au(III) catalysis: Rational development of hemilabile proximity-guided N-heterocyclic carbenes.

In the past two decades, oxidant-free, ligand-enabled gold(I)/gold(III) [Au(I)/Au(III)] catalysis has become a potential complement to palladium(0)/palladium(II) [Pd(0)/Pd(II)] catalysis in diverse transformation, yet broadly general ligands for Au(I)/Au(III) catalysis remain lacking. Herein, we report a platform for ligand-enabled Au(I)/Au(III) catalysis through the rational development of hemilabile ImQun N-heterocyclic carbene (NHC) nitrogen (N),carbon (C) ligands (ImQun = imidazo[1,5-a]quinoline). Intriguingly, the best Au catalyst ImQunDippNMe2AuCl features the shortest distances between the chelating N atom and the Au center for oxidant-free reaction paradigms. The excellent activity has been demonstrated in alkene difunctionalization via the oxidant-free Au(I)/Au(III) cycle through C─O, C─N, and C─C bond formation, including highly challenging aromatic olefins (>60 examples) and late-stage modification of complex pharmaceuticals (>15 examples). Comprehensive density functional theory (DFT) studies have provided fundamental insight into the reaction mechanism and highlight the central effect of this NHC on the Au(I)/Au(III) redox cycle. The facile access to hemilabile, closely coordinating NHC will enable accelerated development of Au(I)/Au(III) oxidant-free reactivity paradigms using powerful Au catalysis.