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, [NH 2(CH 2) 2imMe)] NO 3 ([3][NO 3]) reacted with Ag 2CO 3 in dimethyl sulfoxide readily yielding a Ag(i)-(NHC-NH 2) 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(NH 2(CH 2) 2imMe) 2][NO 3] 2 ([5][NO 3] 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][NO 3] 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) Å that is maintained in solution as documented by the DFT calculations. Complex [5][NO 3] 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.