Wang Mei-Yan, Chen Li, Li Bing-Wen, Liu Jing-Yao
Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China.
Department of Oral Radiology, School and Hospital of Stomatology, Jilin University, Changchun 130021, People's Republic of China.
Dalton Trans. 2020 Mar 3;49(9):2914-2923. doi: 10.1039/c9dt04362d.
The reaction mechanism of bimetallic Pd-Zn-catalyzed cycloaddition of alkynyl aryl ethers with internal alkynes has been studied theoretically. Besides cycloaddition reaction, the dimerization of alkynyl aryl ethers was also considered. Both C6H5OC[triple bond, length as m-dash]CSiiPr3 and C6H5OC[triple bond, length as m-dash]CSiMe3 were chosen as the substrates. The reactions involve C-H activation of the substrate, acetic acid rotation, H transformation, MeC[triple bond, length as m-dash]CMe or substrate insertion into the Pd-phenyl bond and reductive elimination steps. It is found that cycloaddition is favored for C6H5OC[triple bond, length as m-dash]CSiiPr3, while dimerization is preferred for C6H5OC[triple bond, length as m-dash]CSiMe3, because the steric repulsion between two bulky SiiPr3 groups is relatively large and the steric repulsion between two small SiMe3 groups is relatively small. In addition, besides C6H5OC[triple bond, length as m-dash]CSiiPr3, four other substrates C6H5CH2C[triple bond, length as m-dash]CSiiPr3, C6H5C(O)C[triple bond, length as m-dash]CSiiPr3, C6H5SC[triple bond, length as m-dash]CSiiPr3 and C6H5N(H)C[triple bond, length as m-dash]CSiiPr3 have been calculated as the substrates for cycloaddition reaction with MeC[triple bond, length as m-dash]CMe. Among the five substrates, C6H5OC[triple bond, length as m-dash]CSiiPr3 has the lowest energy barrier (29.9 kcal mol-1), consistent with the experimental observation that C6H5OC[triple bond, length as m-dash]CSiiPr3 is the appropriate substrate for successful cycloaddition.
已从理论上研究了双金属钯锌催化的炔基芳基醚与内炔的环加成反应机理。除了环加成反应外，还考虑了炔基芳基醚的二聚反应。选择C6H5OC≡CSi iPr3和C6H5OC≡CSiMe3作为底物。反应涉及底物的C-H活化、乙酸旋转、H转移、MeC≡CMe或底物插入Pd-苯基键以及还原消除步骤。研究发现，对于C6H5OC≡CSi iPr3，环加成反应更有利，而对于C6H5OC≡CSiMe3，二聚反应更受青睐，这是因为两个庞大的Si iPr3基团之间的空间排斥相对较大，而两个较小的SiMe3基团之间的空间排斥相对较小。此外，除了C6H5OC≡CSi iPr3外，还计算了其他四种底物C6H5CH2C≡CSi iPr3、C6H5C(O)C≡CSi iPr3、C6H5SC≡CSi iPr3和C6H5N(H)C≡CSi iPr3作为与MeC≡CMe发生环加成反应的底物。在这五种底物中，C6H5OC≡CSi iPr3具有最低的能垒（29.9 kcal mol-1），这与C6H5OC≡CSi iPr3是成功进行环加成反应的合适底物这一实验观察结果一致。
