Güell Mireia, Martín Nazario, Altable Margarita, Filippone Salvatore, Martín-Domenech Angel, Solà Miquel
Institut de Química Computacional and Departament de Química, Universitat de Girona, Campus Montilivi, E-17071 Girona, Catalonia, Spain.
J Phys Chem A. 2007 Jun 21;111(24):5253-8. doi: 10.1021/jp0705368. Epub 2007 May 25.
Substitution of a H atom by an alkyl group on the terminal carbon of the alkyne moiety of 1,6-fullerenynes has a strong impact on the products of the reaction undergone by this species after thermal treatment. While the reaction of 1,6-fullerenynes bearing an unsubstituted alkyne moiety results in the cycloaddition of the alkyne group to the fullerene double bond leading to cyclobutene-fused derivatives, the presence of an alkyl substituent leads to the formation of allenes. In the present work, we have performed an exhaustive theoretical analysis of all possible reaction mechanisms leading to cyclobutene-fused derivatives and allenes to offer an explanation of the reactivity differences observed. The results obtained show that formation of cyclobutene-fused derivatives occurs through a stepwise diradical reaction mechanism, while allene formation proceeds through a concerted way involving an uncommon intramolecular ene process. For the 1,6-fullerenynes bearing a substituted alkyne, the ene reaction path leading to allenes has an energy barrier somewhat lower than the stepwise diradical mechanism for the cyclobutene-fused derivative formation, thus explaining the outcome of the reaction.
在1,6-富勒烯炔烃的炔烃部分末端碳原子上，用烷基取代氢原子对该物种热处理后所经历反应的产物有很大影响。带有未取代炔烃部分的1,6-富勒烯炔烃反应时，炔烃基团会与富勒烯双键发生环加成反应，生成环丁烯稠合衍生物；而存在烷基取代基时则会生成丙二烯。在本工作中，我们对导致环丁烯稠合衍生物和丙二烯的所有可能反应机理进行了详尽的理论分析，以解释所观察到的反应活性差异。所得结果表明，环丁烯稠合衍生物的形成是通过逐步双自由基反应机理进行的，而丙二烯的形成则是通过涉及不常见分子内烯反应的协同方式进行的。对于带有取代炔烃的1,6-富勒烯炔烃，导致丙二烯生成的烯反应路径的能垒略低于生成环丁烯稠合衍生物的逐步双自由基机理，从而解释了反应的结果。
