L-Shaped Heterobidentate Imidazo[1,5-a]pyridin-3-ylidene (N,C)-Ligands for Oxidant-Free Au I /Au III Catalysis.

In the last decade, major advances have been made in homogeneous gold catalysis. However, Au I /Au III catalytic cycle remains much less explored due to the reluctance of Au I to undergo oxidative addition and the stability of the Au III intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N-heterocyclic carbene) ligands through the development of a new class of L-shaped heterobidentate ImPy (ImPy=imidazo[1,5-a]pyridin-3-ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ-donation of the carbene center in a rigid conformation, imposed by the ligand architecture. Detailed characterization and control studies reveal key ligand features for Au I /Au III redox cycle, wherein the hemilabile nitrogen is placed at the coordinating position of a rigid framework. Given the tremendous significance of homogeneous gold catalysis, we anticipate that this ligand platform will find widespread application.