1,1-Digoldallylium Complexes: Diaurated Allylic Carbocations Indicate New Prospects of the Coordination Chemistry of Carbon.

Reacting (NHC)(cyclopropenyl)gold(I) complexes with cationic gold complexes [(IPr)AuX] afforded extremely reactive allylium-1,1-diido-bridged digold intermediates. We prove the existence and constitution of this structure with FT-ICR-MS/MS, NMR, and UV-vis-NIR experiments and isolated the nucleophilic addition product [(Me)(Ph)(CCHC){Au(IPr)}(SOMe)]NTf with DMSO. Our computational investigation unveiled that the bonding situation of this μ-allylium-1,1-diido digold domain was best described as a three-center-four-electron bond with a π-backbond. The valence orbitals showed extreme delocalization and strong π-interactions between the three centers Au-C-Au. The bridging carbon atom C was best described as trigonal planar sp-hybridized carbon in this structure. Excitation succeeded in UV-vis-NIR measurements with energies as low as near-IR radiation.