Mechanistic Study Of Unsaturated Bond Additions

Owing to increasing demands of catalytic functionalization for organic synthesis,numerous new synthetic methodologies and chemo-selectivity are emerging with the development of unsaturated bond additions.Thus,the development of efficient and highly selective unsaturated bond additions would remain the focus of organic synthetic chemistry.Among the catalytic unsaturated bond additions,the activation strategies and selectivity regulations were certified as core contents.Therefore,understanding the mechanism and revealing the origin of selectivity would play a crucial role in the development of catalytic unsaturated bond additions.In this thesis,theoretical calculations were employed to investigate the mechanism and selectivity for unsaturated bond additions,by using different activation strategies.Research results show that these activation strategies can effectively improve the reactivity as well as control the chemical selectivity.Details are as followings:1.Redox condition mediated diverse transformation of CO₂ in unsaturated bond additions.The combined theoretical and experimental investigation was employed to investigate the transition metal-catalyzed functionalization of CO₂ under different redox conditions.We have constructed the catalytic cycle and clarified the origin of selectivity for unsaturated bond additions of CO₂.Based on the understanding of properties and conversion mechanism for CO₂ by theoretical calculation,the catalytic system of CO₂transformation was optimized and designed accordingly.Supported by gains of mechanistic insight,the catalytic reactivity was effectively regulated by adjusting the redox conditions in the catalytic system,which lead to the diverse syntheses of CO₂.Research results show that CO₂ not only could be introduced as-COO-skeleton but also proceed hydroxy-methylation reactions in oxidative and reductive catalytic systems respectively.Particularly,a catalytic O-H/C-H oxidative carbonylation coupling also could be achieved without additional CO source,in which CO₂ simultaneously plays as oxidant and CO source.These findings would provide theoretical support for the development of catalytic CO₂ fixations.2.Ligand effects mediated catalytic hydrogenation of inert N-heterocycles.We mechanistically investigated the ligand effect in Mn-catalyzed hydrogenation reactions by combining experiments with DFT calculations,as exemplified by the hydrogenation of benzanilide.It is demonstrated that NNP-pincer ligands on the Mn complexes are indeed more electron-rich and less sterically hindered than their PNP counterparts,thus leading to higher reactivity in a series of Mn-catalyzed hydrogenation reactions.Inspired by the discovery of this ligand effect,we first developed the Mn-catalyzed hydrogenation of N-heterocycles using NNP-Mn pincer catalysts.Notably,the activity of PNP-Mn pincer catalysts was much lower than that of their NNP counterparts under the same reaction conditions.Further mechanistic studies confirmed that such a ligand effect is generally applicable in the hydrogenation reactions of both carbonyl and imine substrates based on Mn catalysis.Mechanistic insight gained in this study could help to better interpret the catalytic reactivity and contribute to the rational design of new base metal catalysts.3.Mechanism and selectivity study of bifunctional catalyzed unsaturated bond additions.We have evaluated the reactivity for three bifunctional catalyzed unsaturated bond additions.It is proven that the bifunctional catalyst can simultaneously combine two reaction components,which leads to the reduced entropy loss of intermolecular reaction as well as enhanced reactivity.Meanwhile,the origins of enantioselectivity for bifunctional catalytic systems were also clarified prudently,and theoretically predicted enantioselectivity is consistent with experimental observations.Based on the mechanistic understanding of bifunctional catalysis,we have further developed a method for achieving the enantiodivergence in challenging asymmetric transformations.Simple yet strategic modification of bifunctional catalyst while maintaining the same absolute configuration of the catalysts led to a complete reversal of the enantioselectivity through conformation modulation of the catalyst.These results provide a practical theoretical guide for the design of bifunctional catalysis.