Pounder Austin, Chen Leanne D, Tam William
Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
ACS Omega. 2020 Dec 18;6(1):900-911. doi: 10.1021/acsomega.0c05499. eCollection 2021 Jan 12.
The ruthenium-catalyzed [2 + 2] and homo Diels-Alder [2 + 2 + 2] cycloadditions of norbornadiene with disubstituted alkynes are investigated using density functional theory (DFT). These DFT calculations provide a mechanistic explanation for observed reactivity trends with different functional groups. Alkynyl phosphonates and norbornadiene form the [2 + 2 + 2] cycloadduct, while other functionalized alkynes afford the respective [2 + 2] cycloadduct, in excellent agreement with experimental results. The computational studies on the potential energy profiles of the cycloadditions show that the rate-determining step for the [2 + 2] cycloaddition is the final reductive elimination step, but the overall rate for the [2 + 2 + 2] cycloaddition is controlled by the initial oxidative cyclization. Two distinct mechanistic pathways for the [2 + 2 + 2] cycloaddition, cationic and neutral, are characterized and reveal that Cp*RuCl(COD) energetically prefers the cationic pathway.
利用密度泛函理论（DFT）研究了钌催化的降冰片二烯与二取代炔烃的[2 + 2]环加成反应和同环狄尔斯-阿尔德[2 + 2 + 2]环加成反应。这些DFT计算为观察到的不同官能团的反应活性趋势提供了机理上的解释。炔基膦酸酯和降冰片二烯形成[2 + 2 + 2]环加成产物，而其他官能化炔烃则分别生成各自的[2 + 2]环加成产物，这与实验结果非常吻合。对环加成反应势能面的计算研究表明，[2 + 2]环加成反应的速率决定步骤是最后的还原消除步骤，但[2 + 2 + 2]环加成反应的总速率由初始的氧化环化控制。[2 + 2 + 2]环加成反应有两种不同的机理途径，即阳离子途径和中性途径，其特征表明Cp*RuCl(COD)在能量上更倾向于阳离子途径。
