Symmetry-adapted perturbation theory for organocatalysis
Bakr, Brandon Wallace
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Functional-group and atomic partitions of symmetry-adapted perturbation theory (SAPT) were used, for the first time, to analyze non-covalent interactions thought to influence the selectivity of the Houk-List mechanism for intermolecular Aldol additions and organoboron catalyzed allyl additions to fluoroketones. For the Houk-List mechanism, functional-group partition of symmetry-adapted perturbation theory (F-SAPT) analysis of non-covalent interactions in the transition states that were thought to engender stereoselectivity were not found to be preferentially stabilizing for the transition states leading to the preferred products. This finding runs counter to the prevailing hypothesis that a NCHδ+···δ-O=C contact determines the stereochemical outcome. For the allyl addition to fluoroketones, F-SAPT and the atomic partition of symmetry-adapted perturbation theory (ASAPT) analyses were used to probe the non-covalent contacts that were thought to result in enantioselectivity. ASAPT confirmed all atom-atom interactions that were implicated in the literature as stabilizing or destabilizing, primarily a stabilizing F···H interaction between a fluorine of the fluoroketone and the ammonium proton of the organoboron catalyst. In addition to these studies, tools for performing F-SAPT analyses are presented, and the possibility of using local correlation approximations in double hybrid density functional theory is introduced. Finally, future studies for SAPT analysis of organocatalysis are discussed.