Theoretical Study Of Organic Reactions Catalyzed By Supramolecular Metallocages And Transition Metals

Numerous catalysts,particularly metal catalysts,have been demonstrated to efficiently catalyze a number of organic reactions with the advancement of catalytic research.Single transition metal catalyst is one of the most widely used catalysts in the field of organic synthesis.The double transition metal catalyst can provide multiple binding sites and reactive sites through the synergistic interaction between metals.The supramolecular metal coordination cages formed by metal and organic ligands are simple to prepare and have special hydrophobic cavities,so the reaction mechanism is very different from that of traditional metal catalysts.It is worthy that many organic catalytic systems are quit complicated,making the research of reaction mechanism essential for the development of effective catalysts.In this work,three catalytic systems,supramolecular catalysis,transition monometal catalysis and transition bimetal catalysis,were theoretically studied using theoretical calculations,so as to explore the reaction mechanism and explain the main factors affecting the reaction selectivity,in order to provide certain theoretical guidance for the development of the experiment.The tetrahedral metallocage[Ga₄L₆]^12-developed by Raymond’s group has been reported to selectively catalyzed aza-Prins reactions.However,the molecular weight of the supramolecular metallocage is too large,so the research on the mechanism calculation is not mature.We use the ONIOM model to investigate the reaction mechanism and selectivity,and set the cage as the lower layer,which greatly reduced the calculation cost.The results showed that the substrate forms iminium ions by dehydration condensation,which were then encapsulated in cages.Iminium ions tend to adopt vertical conformation under the extrusion of metallocage,and generate piperidine products through cyclization,proton transfer,hydrolysis and guest exchange.The electrostatic environment in the metallocage,the non-covalent interaction between host and guest,the confinement effects and the hydrophobic effects of metallocage are the important factors that determine the reaction selectivity.Electrostatic interaction is the driving force for the binding of host and guest.The host-guest combination is stabilized by non-covalent interactions.The limited space in the cage is selective to the size of guest molecule,and allows iminium ions to react in a tighter conformation to generate products different from those in bulk.Hydrophobic effect affects selectivity in entropy contribution,which is more favorable for vertical conformational reactions.These influencing factors are obviously different from those in traditional metal catalytic systems.The organic reaction catalyzed by transition metal catalyst mainly uses the combination of transition metal to substrate to achieve the construction of covalent bond,and synthesizes various target products through spatial and electronic effects.Kami L.Hull group reported rhodium-catalyzed selective hydroamination of allyl imines and homoallylic amines,achieving selective control over unactivated olefins.The mechanism and selective control factors of this system are still unclear.We explain the mechanism and selectivity of the system by theoretical calculation.The mechanism of rhodium-catalyzed hydroamination includes substrate coordination,amino-rhodation,proton transfer and reduction elimination.Orbital interaction,catalyst deformation and steric hindrance are the main factors affecting the selectivity when the substrate is homoallylic amines.When the substrate is allyl imines,the electronic effect and the substrate-catalyst interaction are the dominant factors.The interaction intensity between substrate and ligand could improve the activity of the reaction.We calculated the effects of different central metals and ligands on the system,and found that changing the radius of the central metals could change the rate-limiting step,and changing the ligands could realize the regulation of the reaction activity.The modification of benzene ring skeleton has always attracted much attention,especially the destruction of aromatic hydrocarbon C-C bond to modify benzene skeleton is facing a great challenge.Double transition metal catalysts balance the charge of the system through the synergistic interaction between metals,which is more favorable to the activation and catalysis of substrates.In cooperate with Wei Hao’s research group,the aim of this work was to reveal the reaction mechanism and selective source of the double rhodium catalyst catalyzed the nitrogen insertion of benzene ring.The reaction paths of singlet state and triplet state were calculated respectively,and the mechanism of C-H insertion reaction and C-C insertion reaction was explored.The analysis of the spin distribution and electron distribution of the reaction showed that double rhodium catalyst was partially oxidized after the substrate was combined with the catalyst,increasing the electrons on the substrate,thus enhancing the reaction activity.The analysis of the transition state of the two paths shows that the interaction between substrate and catalyst（hydrogen bond interaction）is the main factor determining the selectivity.The purpose of this paper is to explore three different types of catalytic systems（supramolecular catalysis,single transition metal catalysis and double transition metal catalysis）and explain the reaction mechanism as well as the influencing factors that control chemo-/regio-selectivity.Through this work,the different functions and influences of various catalysts are revealed,so as to provide certain theoretical guidance for the development of new catalysts.