Theoretical Examination of the Plausible Reaction Process for Stereoselective Synthesis of Hexapole Helicene via a Palladium-Catalyzed [2 + 2 + 2] Cyclotrimerization of [5]Helicenyl Aryne
Theoretical Examination of the Plausible Reaction Process for Stereoselective Synthesis of Hexapole Helicene via a Palladium-Catalyzed [2 + 2 + 2] Cyclotrimerization of [5]Helicenyl Aryne
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通过钯催化[2 2 2][5]螺烯基芳炔的环三聚反应立体选择性合成六极螺烯的合理反应过程的理论检验
DOI：
10.1021/acs.jpca.9b09533
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发表时间：
2020
期刊：
影响因子：
2.9
通讯作者：
K.
中科院分区：
文献类型：
--
作者：
Hosokawa;T.; Asadaa;T.; Kamikawa;K.
用理论方法研究了钯催化的[2+2+2]环三聚[5]螺烯基芳烃合成六极螺烯的反应机理。在之前的实验研究中，该反应选择性地生成了C2对称的六极螺烯，尽管D3对称结构在热力学上更稳定。为了阐明该反应的机理，用密度泛函理论(DFT)和过渡态理论计算了初级反应的反应轮廓和动力学速率常数。结果表明，[2+2+2]环三聚反应的第一步不是Diels-Alder反应，而是将螺烯基芳烃插入金属环戊二烯。随后，我们澄清了该反应的高自由能势垒阻止了D3对称产物的形成，而在300K时可以获得C2对称产物，并根据估算的动力学速率常数对异构体摩尔分数的时间演化进行了模拟。模拟结果成功地再现了在300K时生成C2对称产物的实验结果，而在400K时异构化为更稳定的D3六极螺烯结构。
The reaction mechanisms of the plausible reaction process for the synthesis of hexapole helicene via a palladium-catalyzed [2 + 2 + 2] cyclotrimerization of [5]helicenyl aryne were examined using a theoretical approach. In a previous experimental study, this reaction selectively producedC2-symmetrical hexapole helicene, even though theD3-symmetrical structure is thermodynamically more stable. To clarify the mechanism underlying this reaction, density functional theory (DFT) and transition-state-theory calculations were used to evaluate the reaction profile and kinetic rate constants of the primary reactions. The thus obtained results suggest that the first step of the [2 + 2 + 2] cyclotrimerization is not a Diels–Alder reaction but an insertion of the helicenyl aryne into a metallacyclopentadiene. Subsequently, we clarified that the formation of theD3-symmetrical product is precluded by the high free-energy barrier of this reaction, while theC2-symmetrical product can be obtained at 300 K. Simulations of the time evolution of the molar fractions of the isomers were carried out based on the evaluated kinetic rate constants. The experimental result that theC2-symmetrical product is formed predominantly at 300 K was successfully reproduced in the simulations, while the isomerization into the more stableD3hexapole helicene structure is predicted to occur at 400 K.