Primary amino-functionalized N-Heterocyclic carbene ligands as support for Au(I)•••Au(I) interactions: structural, electrochemical, spectroscopic and computational studies of the dinuclear [Au2(NH2(CH2)2imMe)2][NO3]2

The N-heterocyclic carbene (NHC) precursor, 1-(2-aminoethyl)-3-methylimidazolium nitrate, [NH2(CH2)2imMe)]NO3 ([3][NO3]) reacted with Ag2CO3 in dimethyl sulfoxide readily yielding a silver Ag(I)-(NHC-NH2) complex presenting limited stability in solution. The in situ carbene transfer reaction of the latter with [Au(tht)Cl] afforded the first example of a dinuclear gold(I) complex [Au2(NH2(CH2)2imMe)2][NO3]2 ([5][NO3]2) bearing a primary amino-functionalized NHC ligand. The complex has been characterized by NMR, mass spectrometry, X-ray crystallography and cyclic voltammetry; the electrochemical behaviour and photophysical properties of [5][NO3]2 have been also investigated and the experimental data have been compared with density functional theory DFT and Time Dependent TDDFT calculations. Single-crystal structural studies showed that the Au(I)-carbene compound contains dinuclear (AuL)2 cations in which pairs of gold(I) centres are linked by a pair of bridging ligands, with a Au•••Au aurophilic contact of 3.2332(17) Ǻ that is maintained in solution as documented by the DFT calculations. Complex [5][NO3]2 is photoluminescent in solution at room temperature and the high energy emission peak at 410 nm is remarkably shifted with respect to the absorption band centred at 260 nm.