Synthesis and Structural Investigation of Rigid Naphthyridine-Bis(carbene) for Trigonal Planar Coordination of Coinage Metals

Coinage metal complexes, particularly Cu(I) and Au(I), supported by N-heterocyclic carbenes are of broad interest in organometallic synthesis, catalysis, and luminescent materials. The d¹⁰ coinage metals can adopt varied linear, trigonal planar, and tetrahedral geometries. However, two-coordinate, linear Cu(I) and Au(I) complexes supported by sterically demanding monodentate or chelating carbenes are generally observed. In most cases, chelating ligands generate multinuclear species with linear geometries at the corresponding Cu(I) centers rather than mononuclear complexes. In this report, we synthesized two bis(carbene) ligands anchored by a flexible bipyridine and a rigid naphthyridine backbone with tunable proximal and distal steric properties at the wingtips to examine the influence of backbone rigidity and directionality of carbene donors on the formation of trigonal planar coinage metal species. The bipyridine-bis(carbene) (ImPy)₂ ligand exclusively stabilizes dinuclear chloride complexes of Cu(I) and Ag(I), whereas the naphthyridine-bis(carbene) (NBC) stabilizes mononuclear, trigonal planar chloride complexes of Cu(I) and Ag(I) and a dinuclear chloride Au(I) complex.