Structure of a Reactive Gold Carbenoid

A formal gold‐for‐chromium transmetalation allowed the gold carbenoid species [Cy3PAuCAr2]NTf2 (11) (Ar=pMeOC6H4‐) to be obtained in crystalline form. The structure in the solid state suggests that there is only little back donation of electron density from gold to the carbene center of 11 and hence very modest AuC double‐bond character; rather, it is the organic ligand framework that is responsible for stabilizing this species by resonance delocalization of the accumulated positive charge. Because 11 is capable of cyclopropanating p‐methoxystyrene even at low temperature, the discussion of its structure is deemed relevant for a better understanding of the mechanisms of π‐acid catalysis in general. Call me “carbenoid”: No signs of significant AuC double‐bond character, but many indications for charge density at carbon distinguish the structure of an only modestly “stabilized” gold carbenoid in the solid state. Because this species is capable of cyclopropanating a styrene derivative under mild conditions, its structural features are relevant for mechanistic discussions of π‐acid catalysis in general.