Stabilized Carbenium Ions as Latent, Z-type Ligands

Controlling the reactivity of transition metals using secondary, sigma-accepting ligands is an active area of investigation that is impacting molecular catalysis. Herein we describe the phosphine gold complexes [(o-Ph2P(C6H4)Acr)AuCl](+) ([3](+); Acr=9-N-methylacridinium) and [(o-Ph2P(C6H4)Xan)AuCl](+) ([4](+); Xan=9-xanthylium) where the electrophilic carbenium moiety is juxtaposed with the metal atom. While only weak interactions occur between the gold atom and the carbenium moiety of these complexes, the more Lewis acidic complex [4](+) readily reacts with chloride to afford a trivalent phosphine gold dichloride derivative (7) in which the metal atom is covalently bound to the former carbocationic center. This anion-induced Au-I/Au-III oxidation is accompanied by a conversion of the Lewis acidic carbocationic center in [4](+) into an X-type ligand in 7. We conclude that the carbenium moiety of this complex acts as a latent Z-type ligand poised to increase the Lewis acidity of the gold center, a notion supported by the carbophilic reactivity of these complexes.