Synthesis of Propargyl-Functionalized NHC Gold Complexes

A series of propargyl functionalized N-heterocyclic carbene gold­(I) complexes have been synthesized from the corresponding imidazolium salts with tetrabutylammonium acetylacetonate in the presence of a gold­(I) precursor in a one-pot reaction. Several complexes of different stoichiometries are described: [AuBr­(NHC)], [Au­(NHC)2]­Br and [Au­(C6F5) (NHC)], and many of these have been characterized by X-ray diffraction studies. Aurophilic interactions are present in the compounds bearing less sterically hindered carbenes, and secondary interactions such as hydrogen bonds, π–π stacking, or weak contacts of the gold center with the carbon of the propargyl unit have also been found. These complexes possess a high degree of water solubility, which makes them potentially useful for the synthesis of biologically active compounds or as gold catalysts in water. Activation of the propargyl unit in [AuBr­(NHC)] complexes leads to the formation of interesting trimers with bridging bidentate C∧C alkynyl-carbene ligands.