Probing the Steric Limits of Carbon-Gold Bond Formation: (Dialkylbiarylphosphine)gold(I) Aryls

Aryl-group transfer from arylboronic acids to gold has emerged as a functionally tolerant alternative to classical lithiation- and magnesiation-based synthesis of arylgold(I) species. Here, the scope of the reaction is explored with attention to the sterics of the boronic acid starting material and the supporting ligand on gold. Dicyclohexylbiaryl phosphines are selected as supporting ligands on gold(I) because of their substantial bulk. Aryl-group transfer is compatible with steric buildup on either reaction partner. The structural preference of gold(I) for linear, two-coordinate geometries circumvents potential steric clashes. The new organometallics likely gain added stability through dative interactions with the flanking phosphine biaryl arm and, in three cases, through pi-interactions with the aryl ligand sigma-bonded to gold. The new compounds are characterized by multinuclear NMR and optical spectroscopy, X-ray diffraction crystallography, and combustion analysis. All compounds absorb ultraviolet light at wavelengths lambda < 325 nm. Time-dependent density-functional theory calculations find that multiple singlet-singlet transitions account for the absorption profile, which has both intraligand and (ligand-metal)-to-ligand charge-transfer character.