Exploring the effects of wingtip and linker substituents of the 2,6-dimethyl pyridyl- and 2,6-pyridyl-linked CNC ligands on the coordination chemistry of copper(i) and the solution-phase behavior of the CU-CNC complexes

N-heterocyclic carbenes have recently been used as the supporting ligand of many transition metal complexes that have found their way as catalysts or co-catalysts in assisting various organic reactions. The NHC-containing structures range from centering around the carbene with large heterocycles connected to the backbone or wingtips to using a coordinating group like a pyridine ring linking two carbene units. Recently, we have reported Cu(I) complexes bound to the pyridine-linked bis-NHC ligands (ref 1). Our computational studies have shown a notable contribution from the pyridine moiety to these complexes' frontier orbitals of the Cu(I)-CNC unit. Here, we present the synthesis and characterization of a new class of Cu(I)-CNC complexes bearing para- and meta-substituted pyridine linkers, which appear as binuclear or trinuclear units in the solid state depending on the pyridine derivative. Also, we present the application of these complexes in air-assisted Sonogashira-type and Ullmann-type C-C coupling reactions.