A Gold Exchange: A Mechanistic Study of a Reversible, Formal Ethylene Insertion into a Gold(III)鈥揙xygen Bond

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• 作者：Eirin Langseth ; Ainara Nova ; Eline Aa. Tr氓seth ; Frode Rise ; Sigurd 脴ien ; Richard H. Heyn ; Mats Tilset
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 16, 2014
• 年：2014
• 卷：136
• 期：28
• 页码：10104-10115
• 全文大小：604K
• ISSN：1520-5126

文摘

The Au(III) complex Au(OAc^F)₂(tpy) (1, OAc^F = OCOCF₃; tpy = 2-p-tolylpyridine) undergoes reversible dissociation of the OAc^F ligand trans to C, as seen by ¹⁹F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between 1 and ethylene produces Au(OAc^F)(CH₂CH₂OAc^F)(tpy) (2). The reaction is a formal insertion of the olefin into the Au鈥揙 bond trans to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au(OAc^F)(CH₂CH₂OCH₂CF₃)(tpy) (3) is formed as the major product. Both 2 and 3 have been characterized by X-ray crystallography. In TFA/TFE mixtures, 2 and 3 are in equilibrium with a slight thermodynamic preference for 2 over 3. Exposure of 2 to ethylene-d₄ in TFA caused exchange of ethylene-d₄ for ethylene at room temperature. The reaction of 1 with cis-1,2-dideuterioethylene furnished Au(OAc^F)(threo-CHDCHDOAc^F)(tpy), consistent with an overall anti addition to ethylene. DFT(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc^F trans to N by ethylene. Addition of free ^{鈥?/sup>OAcF to coordinated ethylene furnishes 2. While substitution of OAcF by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH₂CH₂OAcF trans to C accounts for the selective formation of 2. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH₂Cl₂ arise from stabilization of the 鈥?/sup>OAcF anion lost during the first reaction step.}