Rearrangement of a Transient Gold Vinylidene into Gold Carbenes.

The gold acetylide complex 20 endowed with a biaryl backbone provides opportunities for a study on the formation and fate of gold vinylidenes. Although the formyl group in 20 is not sufficiently electrophilic to get attacked by the acetylide in proximity, its activation with TBSOTf (TBSOTf=tert-butyldimethylsilyl trifluoromethanesulfonate) at low temperature triggered instantaneous formation of a gold vinylidene (21). This metastable species evolved into the cationic gold carbene complex 22 bearing a phenanthrene unit and a hydroxyl group at the aurated center; the recorded data suggest that this product might be better viewed as an acylgold species protonated by triflic acid. The use of [Me3 O⋅BF4 ] as the activating agent led to formation of the analogous Fischer-type carbene 24, whereas replacement of gold by the [CpRu(PPh3 )2 ]+ fragment allowed the ruthenium vinylidene 27 to be isolated, which closely resembles the proposed gold intermediate 21. The starting gold complex 20, the derived products 22 and 24, as well as vinylidene 27 were characterized by X-ray diffraction.