Synthesis and Characterization of Gold(I) Complexes of Dibenzotropylidene-Functionalized NHC Ligands (Trop-NHCs)

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 (<b>R-1</b>) were generated in a single step using <i>N</i>-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)] (<b>R-3</b>) and the cationic bis-NHC-coordinated complexes [(NHC)₂Au]­BArF₂₄ (<b>R-4</b>), respectively. The Gagosz-type complexes <b>R-3</b> were further tested in the hydration of diphenylacetylene, showing a clear trend in activity depending on the ligand’s sensitivity to hydrolysis