Role of σ,π-Digold(I) Alkyne Complexes in Reactions of Enynes

Gold­(I) acetylide and σ,π-digold­(I) alkyne complexes derived from one prototypical 1,6-enyne and from 7-ethynyl-1,3,5-cycloheptatriene have been prepared and structurally characterized. Their possible role in gold­(I)-catalyzed cycloisomerizations has been studied by experiment and by DFT calculations. Gold­(I) acetylides are totally unproductive complexes in the absence of Brønsted acids. Similarly, no cyclizations were observed by heating σ,π-digold­(I) alkyne digold­(I) at least up to 130 °C. Theoretical studies provide a rationale for the much lower reactivity of digold species in reactions of enynes.