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

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Abstract
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 Ag(I)-(NHC-NH2) complex presenting limited stability in solution. The in situcarbene 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) Å 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.

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