Isolation and characterization of gem-diaurated species having two C-Au σ bonds in gold(I)-activated amidiniumation of alkynes

We have investigated the ligand effect on the gold-activated intramolecular amidiniumation of formamidine having a terminal alkyne, and observed the transformation of vinyl gold species into a gem-digold intermediate comprising two C-Au sigma bonds, which represents a new binding mode for gem-digold species in the gold-promoted transformation of alkynes.