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.