1,3-Rearrangement Mechanism Of Allyl-ammonium By Light Mediated Supramolecular Catalysis Of [Ga₄L₆]^12-:Theoretical Study

Supramolecular cage compounds have variable and adjustable reaction cavities,so they can be used to catalyze chemical reactions that are usually considered difficult or impossible,and even change the reaction selectivity.This has attracted the attention and extensive research of chemists.Therefore,the use of supramolecular cages to catalyze chemical reactions has become an important area of research in enzyme-mimetic catalysis.The continuous development of this field urgently requires a deeper understanding of the essential role of cages in catalyzing the reactions occurring in the guest molecule.This provides directions for the future design and synthesis of more complex molecular cages.However,the limitations of experimental techniques have led to a lack of clear understanding of the mechanism of supramolecular cages in catalytic chemical reactions,which greatly limits the further application of supramolecular cage catalysis.Modern quantum chemical calculations,which simulate the structural,electronic,and energetic characteristics of molecules in the system through computational chemistry software,have become indispensable tools for revealing the reaction mechanism.In this paper,we systematically explored the reaction mechanism by using the molecular dynamics（MD）simulations and density functional theory（DFT）to select the classical[Ga₄L₆]^12-to catalyze the 1,3-rearrangement reaction of allyl ammonium as a model.Clarifying the nature of[Ga₄L₆]^12-catalytic action and the reasons for the different selectivity produced in the cage compared to that in solution.To provide theoretical support for the development and design of more complex molecular cages and the strategy of[Ga₄L₆]^12-catalyzed chemical reactions.The first chapter of this thesis introduces the basic concepts of catalysts and catalysis,mimetic enzyme catalysis and supramolecular catalysis,and outlines the progress of supramolecular research and the unique catalytic role of metal-organic molecular cages,with emphasis on the application of supramolecular cages[Ga₄L₆]^12-in catalytic chemical reactions.Chapter 2 deals with theoretical foundations and computational methods,including quantum chemical fundamentals,density functional theory,transition state theory,and molecular dynamics simulations.The relevant research work of the author during master’s degree is distributed in Chapters 3 and 4,and the main contents are as follows:1.The MD simulation of the supramolecular cage[Ga₄L₆]^12-in vacuum phase and solution were successfully completed using MD methods to clarify the number of solvent molecules within the cavity of the cage.In addition,the comparative study of the encapsulation of[Ga₄L₆]^12-on H⁺,OH^?,allyl ammonium cation and Br^?showed that the cage has electrostatic attraction for cations and electrostatic repulsion for anions.The analysis of the electrostatic potential of[Ga₄L₆]^12-shows that[Ga₄L₆]^12-shows negative electrical properties inside the cage,which is consistent with the anionic nature of the molecular cage cavity.In addition,we investigated the photophysical properties of[Ga₄L₆]^12-and found that[Ga₄L₆]^12-absorbs strongly in the UV region.It provides a basic model for further exploration of the nature molecular cage catalysis.2.The reaction mechanism of the light-mediated supramolecular cage[Ga₄L₆]^12-catalyzed1,3-rearrangement of allyl-ammonium was explored using DFT.The results show that[Ga₄L₆]^12-photocatalyzed allyl-ammonium proceeds through the electron transfer mechanism rather than the energy transfer mechanism,which in turn catalyzes C-N bonding to obtain 1,3-rearrangement products.Among them,C-N bonding is the critical step of the reaction.The essential reasons for the supramolecular cage[Ga₄L₆]^12-catalyzed 1,3-rearrangement reaction of allyl-ammonium without the[2+2]cycloaddition reaction can be divided into two points:firstly,the generation of active intermediates between the cage and the substrate through the electron transfer mechanism that allows for subsequent reactions;secondly,the anionic environment inside the cage facilitates Br^?overflow out of the cage,which in turn triggers the1,3-rearrangement reaction inside the cage.The exchange of solvent molecules and allyl-ammonium in[Ga₄L₆]^12-was accomplished during the reaction,and the cage had the pre-organized function on the conformation of the reactants.The present work provides theoretical guidance for the design,synthesis and modification of more complex novel and efficient supramolecular cage catalytic systems.