Gold(I) complexes bearing N-heterocyclic carbenes (NHC) of the type (NHC)AuBr (3a/3b) [NHC = 1-methyl-3-benzylimidazol-2-ylidene (= MeBnIm), and 1,3-dibenzylimidazol-2-ylidene (= Bn 2 Im)] are prepared by transmetallation reactions of (tht)AuBr (tht = tetrahydrothiophene) and (NHC)AgBr (2a/2b). The homoleptic, ionic complexes [(NHC) 2 Au]Br (6a/6b) are synthesized by the reaction with free carbene. Successive oxidation of 3a/3b and 6a/6b with bromine gave the respective (NHC)AuBr 3 (4a/4b) and [(NHC) 2 AuBr 2 ]Br (7a/7b) in good overall yields as yellow powders. All complexes were characterized by NMR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Reactions of the Au(III) complexes towards anionic ligands like carboxylates, phenolates and thiophenolates were investigated and result in a complete or partial reduction to a Au(I) complex. Irradiation of the Au(III) complexes with UV light yield the Au(I) congeners in a clean photo-reaction.

Six examples from a series of complex salts containing bis(1,3-dialkylimidazol-2-ylidene)silver(I) cations (with dialkyl = dimethyl, diethyl, methyl, ethyl, diisopropyl) with [PF 6 ] − , [SbF 6 ] − , [ClO 4 ] − , or [AgBr 2 ] − anions, respectively, were prepared in high yields and characterized by elemental analysis, 1 H and 13 C NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction experiments reveal unprecedentedly large contractions of the metallophilic Ag(I)−Ag(I) distances in the solid-state structures upon cooling. In the salt containing diisopropylsubstituted ligands and [PF 6 ] − anions, a contraction from 3.498(8) to 3.180(2) Å was observed on cooling from 293(1) to 100(1) K. Photochemical measurements show strong hypsochromic shifts of the emission maxima upon cooling, underlining the metallophilic-based nature of the emission bands. Ab initio calculations show that the strong temperature dependence of the observed Ag−Ag distances can be attributed to some extent to both the shallowness and the anharmonicity of the intermetallic interaction potential. The Ag−Ag interaction potentials are found to be attractive only when relativity is accounted for in the calculations.

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