Bridged Pyrroloindole‐CAYC‐Gold Complexes: Harnessing Weak Secondary Intramolecular Au···H−C( <i> sp ³ </i> ) Interactions in Gold(I) Catalysis

Abstract

ABSTRACT Gold(I) catalysis has been established as a tremendously powerful tool in organic synthesis and catalysis. Herein, we introduce a new class of electronically‐ and sterically‐hindered N‐heterocyclic carbene ligands, termed as bridged cyclic amino(ylide)carbene ( b CAYC), containing 9H‐pyrrolo[1,2‐a]indoles as the carbene core and diaryl sulfonium as the ylide partner. Highly electron‐rich b CAYC ligands are suitable for synthesizing the corresponding gold(I) complexes, which exhibit a weak intramolecular Au···H−C(sp 3 ) interaction as a secondary interaction where the gold d‐orbitals act as electron donors and the C–H σ* orbitals act as acceptors. Properties and parameters of Au···H−C(sp 3 ) interactions were investigated through X‐ray, NMR, DFT, AIM, and NBO studies. This study reports a remarkably short Au···H−C(sp 3 ) distance of 2.26 Å, as determined through X‐ray crystallographic analysis. DFT and TEP data analysis revealed that b CAYCs are among the most σ‐donating carbene ligands to date, than other widely used NHC ligands. The steric impact of b CAYCs has shown excellent potential for steric shielding, with %V bur reaching up to 42.6%. These unique properties were well‐reflected through the room‐temperature hydroamination and one‐pot C–N and C–C bond‐forming reactions.