Synthesis and Characterization of Silver(I), Gold(I), and Gold(III) Complexes Bearing Amino-Functionalized N-Heterocyclic Carbenes

Abstract

1-[2-(Dialkylamino)ethyl]-3-methylimidazolium salts (alkyl = Me (1a), i-Pr (1b)) have been prepared and used as precursors for the synthesis of the corresponding [(NHC)2Ag][AgCl2] complexes (NHC = N-heterocyclic carbene, Me (2a), i-Pr (2b)). Upon treatment of 2a with HBF4, crystals of the unprecedented, NHC-stabilized silver cluster [(NHC)4Ag10Cl10] (5) were obtained and characterized by X-ray diffraction. The crystal structure reveals that the carbene carbon atom exists in the rare μ2-coordination pattern, bridging two Ag(I) atoms with further stabilization of the cluster by numerous argentophilic interactions and a coordination of the amino nitrogen donor to one of the silver atoms. Transmetalation of 2a,b with (R2S)AuCl leads to the respective Au(I) complexes 3a,b, which are further oxidized with Br2 to (NHC)AuBr2Cl (4a,b). In red crystals of 4a the gold atom is coordinated in the unusual square-pyramidal geometry with the amine nitrogen atom in the axial position. Upon dissolution in wet organic solvents the amino group is protonated and the color changes to yellow. In square-planar Au(III) halide complexes electronic absorption spectra are dominated by LMCT absorption bands, but in the case of a square-pyramidal coordination sphere the d z 2 orbital is destabilized, becoming the HOMO and causing a low-energy d–d absorption. This interpretation is supported by DFT calculations.

Synthesis and characterization of silver(I), gold(I), and gold(III) complexes bearing a bis-dialkylamino functionalized N-heterocyclic carbene

“…The C2 carbene atom of the Au(III) complex resonates at 173.1 ppm. All chemical shifts of the C2 atoms are in accordance with related dialkylamino-functionalized complexes [12].…”

“…Sharp peaks are obtained when the measurement is performed in D 2 O. A comparable behavior was observed for the related Au(III) complex bearing amino-functionalized 1-[2-(Dialkylamino)ethyl]-3-methylimidazol-2-ylidene ligands [12]: its amino function is partially protonated by solvent moisture also causing broad signals.…”

“…Previously, we reported about acidebase equilibria of solutions of Au(III) complexes bearing 1-[2-(dialkylamino)ethyl]-3-methylimidazol-2-ylidene ligands [12]. The amino-function of these complexes can be reversibly protonated causing a distinct color change from red to yellow which is due to a transition from a squareplanar to a square-pyramidal coordination geometry of the gold atom.…”

Synthesis, Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5‐a]quinolinol Scaffold

“…As observed for other mixed (NHC)AuXY 2 (X, Y = halide) complexes, the more electronegative chloride is in a trans position relative to the carbene carbon atom. [21,23] All Au-C and Au-www.eurjic.org FULL PAPER halide distances are in the expected range. Compared with 5, the Au···O distance decreases significantly to 2.717(1) Å, presumably due to the higher charge of the coordinated metal.…”

“…This is in contrast to a related aminefunctionalized NHC ligand in which a square-pyramidal coordination was observed although the pendant amine was not forced due to the rigidity of the ligand framework. [21] Other examples of a square-pyramidal coordination environment are documented for diimine-type ligands such as phen and 2,2Ј-bipyridine in [(NʝN)AuCl 3 ] complexes. [29] This coordination geometry was also found for the corresponding Au III complex bearing ligand A.…”