Preparation and Metalation of N-Heterocyclic Carbene Ligands with Sterically Tunable 2,6-dialkoxyphenyl Wingtip Groups

Abstract

N-Heterocyclic carbenes (NHCs) featuring 2,6-dialkoxyphenyl wingtip groups are synthesized, and their coordination chemistry and properties are studied. Linear [(NHC)CuCl] complexes composed of ligands synthesized herein were characterized by X-ray crystallography and used to analyze the ligand steric parameters. We demonstrate that the use of different alkyl halides in the preparation of these ligands results in NHCs that are sterically tunable and potentially capable of hemilability. Furthermore, the electronic properties of these ligands are assessed by computational methods, which demonstrate these NHCs to be highly electron donating in nature. Additional metalation of these ligands to sulfur, silver, and palladium is reported, and the resulting palladium complexes are tested in the Suzuki–Miyaura reaction of challenging aryl chlorides to benchmark catalytic activity. A direct correlation between steric impacts and catalytic performance is observed.