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

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• 作者：Christoph Topf ; Christa Hirtenlehner ; Manfred Zabel ; Manuela List ; Michel Fleck ; Uwe Monkowius
• 刊名：Organometallics
• 出版年：2011
• 出版时间：May 23, 2011
• 年：2011
• 卷：30
• 期：10
• 页码：2755-2764
• 全文大小：1085K
• 年卷期：v.30,no.10(May 23, 2011)
• ISSN：1520-6041

文摘

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 渭₂-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_z² orbital is destabilized, becoming the HOMO and causing a low-energy d鈥揹 absorption. This interpretation is supported by DFT calculations.