Synthesis, molecular structures and solution NMR studies of N-heterocyclic carbene–amine silver complexes

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• 作者：Luigi Busetto ; M. Cristina Cassani ; Cristina Femoni ; Alceo Macchioni ; Rita Mazzoni ; Daniele Zuccaccia
• 关键词：Imidazolium salts ; N-Heterocyclic carbene ligands ; Silver complexes ; PGSE ; NOE NMR
• 刊名：Journal of Organometallic Chemistry
• 出版年：2008
• 期刊代码：64_0022328x
• 类别：ch
• 出版时间：15 July 2008
• 卷：693
• 期：15
• 页码：2579-2591
• 文件大小：1097 K

摘要

The synthesis of the Boc-protected 1-(2-aminoethyl)-3-methylimidazolium salts [BocNHCH₂CH₂ImMe]X [2]X (X = I, PF₆) and their straightforward transformation into [NH₂CH₂CH₂ImMe]X [3]X is reported. The reaction between [2]X and Ag₂O leads to the formation in the solid state of three different bonding motifs: a biscarbene salt [(NHC–NHBoc)₂Ag]PF₆ ([4]PF₆, NHC–NHBoc = 1-(2-BocNH-ethyl)-3-methyl-imidazolin-2-ylidene), a tetranuclear complex [Ag(NHC–NHBoc)₂]₂[Ag₂I₄], (5), and a polymeric silver “staircase” [(NHC–NHBoc)₂–Ag₄–I₄]_n, (6) composed of Ag₄I₄ clusters. The same reaction carried out with [3]I showed that a primary silver mono-NHC–NH₂ carbene complex of the type [(NHC–NH₂)AgI] (7) is likely to form but it is unstable in solution. The solid state molecular structures of [4]PF₆, 5 and 6 were determined by X-ray diffraction analysis, whereas PGSE NMR experiments were employed to investigate the hydrodynamic dimension of the imidazolium salts and silver complexes and, consequently, to gain information on the level of aggregation in solution. PGSE NMR studies were complemented by NOE NMR investigations in order to obtain information on anion–cation relative orientation within aggregates.