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

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.