Talmazan Radu A, Liedl Klaus R, Kräutler Bernhard, Podewitz Maren
Institute of General, Inorganic and Theoretical Chemistry, and Centre of Molecular Biosciences, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria.
Org Biomol Chem. 2020 Jun 7;18(21):4090-4103. doi: 10.1039/d0ob00520g. Epub 2020 May 19.
Ever since the discovery of fullerenes, their mono- and multi-functionalization by exohedral addition chemistry has been a fundamental topic. A few years ago, a topochemically controlled regiospecific difunctionalization of C fullerene by anthracene in the solid state was discovered. In the present work, we analyse the mechanism of this unique reaction, where an anthracene molecule is transferred from one C mono-adduct to another one, under exclusive formation of equal amounts of C and of the difficult to make, highly useful, antipodal C bis-adduct. Our herein disclosed dispersion corrected DFT studies show the anthracene transfer to take place in a synchronous retro Diels-Alder/Diels-Alder reaction: an anthracene molecule dissociates from one fullerene under formation of an intermediate, while undergoing stabilizing interactions with both neighbouring fullerene molecules, facilitating the reaction kinetically. In the intermediate, a planar anthracene molecule is sandwiched between two neighbouring fullerenes and forms equally strong 'double-decker' type π-π stacking interactions with both of these fullerenes. Analysis with the distortion interaction model shows that the anthracene unit of the intermediate is almost planar with minimal distortion. This analysis highlights the existence of simultaneous noncovalent interactions engaging both faces of a planar polyunsaturated ring and two convex fullerene surfaces in an unprecedented 'inverted sandwich' structure. Hence, it sheds light on new strategies to design functional fullerene based materials.
自从富勒烯被发现以来，通过外表面加成化学对其进行单官能化和多官能化一直是一个基础课题。几年前，人们发现了蒽在固态下对C富勒烯进行的拓扑化学控制的区域特异性双官能化反应。在本工作中，我们分析了这一独特反应的机理，即一个蒽分子从一个C单加合物转移到另一个C单加合物，同时仅生成等量的C以及难以制备但非常有用的对映体C双加合物。我们在此公开的色散校正密度泛函理论（DFT）研究表明，蒽的转移是通过一个同步的逆狄尔斯-阿尔德/狄尔斯-阿尔德反应发生的：一个蒽分子在形成中间体的过程中从一个富勒烯上解离，同时与两个相邻的富勒烯分子发生稳定相互作用，从而在动力学上促进了反应。在中间体中，一个平面的蒽分子夹在两个相邻的富勒烯之间，并与这两个富勒烯形成同样强的“双层”型π-π堆积相互作用。用畸变相互作用模型进行分析表明，中间体中的蒽单元几乎是平面的，畸变最小。这一分析突出了一种前所未有的“反三明治”结构中，平面多不饱和环的两个面与两个凸面富勒烯表面同时存在非共价相互作用。因此，它为设计基于富勒烯的功能材料提供了新策略。
