Synthesis and characterization of gold(I) complexes of dibenzotropylidene-functionalized NHC ligands (Trop-NHCs)

Abstract

Gold(I) complexes of dibenzotropylidene-functionalized N-heterocyclic carbene ligands (Trop-NHCs) have been prepared in order to investigate their structural features and to reveal possible interactions of the olefin unit with the metal center. The precursor imidazolium chloride salts (R-1) were generated in a single step using N-substituted imidazoles (R = H, Me, DiPP, Ad) and 1 or 2 equiv of Trop-Cl, generating unsymmetrical and symmetrical NHC-olefin hybrids. The structural parameters of the ligands were determined by synthesis and X-ray diffraction analysis of their corresponding gold(I) chloride complexes, revealing highly flexible steric demands of the Trop unit. Conversion of these complexes with halide-abstracting reagents such as AgNTf2 and NaBArF24 cleanly gave neutral, NTf2-coordinated complexes of the type [(NHC)Au(NTf2)] (R-3) and the cationic bis-NHC-coordinated complexes [(NHC)2Au]BArF24 (R-4), respectively. The Gagosz-type complexes R-3 were further tested in the hydration of diphenylacetylene, showing a clear trend in activity depending on the ligand’s sensitivity to hydrolysis.