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 AgSbF 6 with terminal arylacetylenes led to the formation of thermally unstable gold π-alkyne complexes of the form [(IPr)Au(η 2 -HC≡CAr)] + SbF 6 – 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 (η 1,η 2 -C≡CAr)} + SbF 6 –, three of which were isolated in 99% yield and one of which was characterized by X-ray crystallography. 1 H 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.