Department of Chemistry and ‡Centre for Theoretical and Computational Chemistry (CTCC) Department of Chemistry, University of Oslo , P.O. Box 1033, Blindern, N-0315 Oslo, Norway.
J Am Chem Soc. 2014 Jul 16;136(28):10104-15. doi: 10.1021/ja504554u. Epub 2014 Jul 1.
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 (19)F 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-O 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 (-)OAc(F) to coordinated ethylene furnishes 2. While substitution of OAc(F) by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH2CH2OAc(F) 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 (-)OAc(F) anion lost during the first reaction step.
三价金配合物 Au(OAc(F))2(tpy)（1，OAc(F) = OCOCF3；tpy = 2-对甲苯吡啶）通过（19）F NMR 可见其反式 C 位上的 OAc(F)配体发生可逆解离。在二氯甲烷或三氟乙酸（TFA）中，1 与乙烯反应生成 Au(OAc(F))(CH2CH2OAc(F))(tpy)（2）。该反应是烯烃分子插入 Au-O 键反式 N 的形式。在 TFA 中，该反应在环境温度下不到 5 分钟即可完成，而在二氯甲烷中则需要 1 天。在三氟乙醇（TFE）中，主要产物为 Au(OAc(F))(CH2CH2OCH2CF3)(tpy)（3）。2 和 3 均通过 X 射线晶体学进行了表征。在 TFA/TFE 混合物中，2 和 3 处于平衡状态，热力学上更倾向于 2。在 TFA 中，2 与乙烯-d4 接触导致室温下乙烯-d4 与乙烯交换。1 与顺-1,2-二氘代乙烯反应得到 Au(OAc(F))(threo-CHDCHDOAc(F))(tpy)，与乙烯的整体反式加成一致。密度泛函理论（PBE0-D3）计算表明，该反应的第一步是由乙烯通过反式 N 取代 OAc(F)。向配位的乙烯中加入游离的(-)OAc(F)得到 2。虽然乙烯反式 C 位取代 OAc(F)的势垒较低，但动力学和热力学上更倾向于反式 C 位为 CH2CH2OAc(F)的异构体，这导致了 2 的选择性形成。DFT 计算表明，与二氯甲烷相比，在 TFA 和 TFE 中观察到的更高反应速率是由于在第一个反应步骤中失去的(-)OAc(F)阴离子的稳定化所致。
