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)(2)imMe)]NO3 ([3][NO3]) reacted with Ag2CO3 in dimethyl sulfoxide readily yielding a 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 [Au-2(NH2(CH2)(2)-imMe) (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 center dot center dot center dot Au aurophilic contact of 3.2332(17) angstrom 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 centered at 260 nm.