Luminescent Three-Coordinate Copper(I) Complexes Supported by an 8-Aryl-1-Naphthyl-Substituted “Sandwich” NacNac Ligand

Abstract

Sterically encumbered β-diketiminate (NacNac) ligands are widely used in several contexts, and our group recently showed they are effective at preventing excited-state distortion in copper(I) chromophores and increasing their lifetime. This work introduces compounds based on an 8-aryl-1-naphthyl-substituted “sandwich” NacNac ligand, hypothesized to impart even more steric protection than conventional NacNac ligands. We describe a series of Cu(I) heteroleptic compounds (Cu1–Cu7) where the “sandwich” NacNac ligand is paired with aryl isocyanides. The compounds are characterized spectroscopically and by cyclic voltammetry, with the formal Cu^II/Cu^I redox potential occurring near the ferrocene couple and minimally dependent on the isocyanide. In four crystallographically characterized complexes, we observe percent buried volume (%V_bur) parameters of 67.4–71.6% for the “sandwich” NacNac, exceeding that of the common 2,6-diisopropylphenyl (Dipp) NacNac (%V_bur = 59.0–62.9% in related compounds). Despite the enhanced steric bulk, the compounds are only photoluminescent at 77 K, which we attribute to the photophysical noninnocence of the 8-aryl-1-naphthyl groups, which quench the phosphorescence at room temperature. Despite their photophysical limitations, this work suggests that such “sandwich” NacNac ligands are effective at increasing the steric bulk around the metal center, which could be useful in applications in catalysis and small-molecule activation.