Cationic Gold(I) π-Complexes of Terminal Alkynes and Their Conversion to Dinuclear σ,π-Acetylide Complexes

Treatment of a suspension of (IPr)­AuCl [IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene] and AgSbF6 with terminal arylacetylenes led to the formation of thermally unstable gold π-alkyne complexes of the form [(IPr)­Au­(η2-HCCAr)]+SbF6– in ≥86 ± 5% yield, which were characterized by spectroscopy without isolation. Warming these complexes to 0 °C led to C­(sp)–H bond cleavage and formation of dinuclear gold­(I) σ,π-acetylide complexes of the form {[(IPr)­Au]2(η1,η2-CCAr)}+SbF6–, three of which were isolated in 99% yield and one of which was characterized by X-ray crystallography. 1H NMR analysis of the conversion of gold π-arylacetylene complexes to σ,π-acetylide complexes established protonation of free arylacetylene, indicating the generation of a strong Brønsted acid under reaction conditions.