Computational Chemistry as a Tool for Understanding Non-Covalent Interactions in Organic Reactions and Materials
Sepulveda Camarena, Diana
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Non-covalent interactions (NCIs) play vital roles in many areas of chemistry and materials science. Although there has been a great deal of progress understanding the nature of non-covalent interactions in recent years, many aspects of these phenomena are still unclear. Modern DFT methods have become a valuable tool for organic chemists in studies of systems in which dispersion-driven NCIs are vital. The role of non-covalent interactions in two organocatalyzed reactions and two novel organic materials were studied by means of these and other computational tools. The two organocatalyzed reactions presented are the allylation and propargylation reactions catalyzed by a bipyridine N,N?-dioxide catalyst and a hetero-Diels ? Alder reaction catalyzed by a cage-shaped borate catalyst. In the first case, the reaction was used as an example to benchmark DFT methods against high accuracy ab initio calculations. It was shown that B97-D/TZV(2d,2p) provides the best compromise of accuracy and computational efficiency. Additionally, it was demonstrated that the original transition state model used to explain the stereoselectivity of these reactions is flawed. We developed a simple model based on non-covalent electrostatic interactions that explains the stereoselectivity of these reactions as well as the fact that the propargylation reaction is less stereoselective than the allylation. For the second reaction, preliminary results provide some support that ?-stacking interactions between the substrate and the catalyst are responsible for the selective reaction of aromatic over aliphatic aldehydes, as observed experimentally. In an effort to better control the properties of organic materials based on discotic systems, stacking interactions between contorted hexabenzocoronene (c-HBC) homodimers and complexes of c-HBC with C60 fullerene were studied using DFT methods. It was found that the preference to stack as homo or heterodimers can be tuned by controlling the curvature of the c-HBC. To achieve this, different substituents on the c-HBC were tested. However, only perfluorination imparts sufficient curvature to the c-HBC to lead to tip the balance towards heterodimer formation over homodimer formation. Finally, an additional explanation was provided for the rotational speed difference between the ?OH and ?OMe substituted pillararenes. It is shown that in addition to the hydrogen bond explanation for the ?OH substituted case provided by Ogishi and coworkers (J. Phys.Chem. Lett.,2010, 817), non-covalent CH/? interactions contribute significantly to the TS stabilization of the ?OMe substituted case, enhancing the rotational speed.