Theoretical View On Stability And Reactivity Of Manganese Dioxygen Adduct Supported By Calix[4] Arene Ligand

Metal-dioxygen ?M-O₂? complexes, as the key intermediates in the activation of dioxygen by metalloenzymes, have been attracting widespread attention. They can efficiently catalyze the oxidation of alkanes, alkenes, phenol and so on. It was found that the binding modes of dioxygen always lead to different electronic structures and reactivities of metal-dioxygen complexes. Therefore, research on the geometric and electronic structures of metal-dioxygen complexes is of great interest in controlable synthesis of novel dioxygen complexes. Due to the complexity of the synthesis conditions and the limitations of experimental technology, it is difficult to study the geometric and electronic structures by only experimental methods. In this work, we take the calix[4]arene ligated Mn-dioxygen adduct as model system and performed spin-unrestricted density functional theory ?DFT? calculations on it. We investigated the coordination modes between dioxygen and center metal and explored the reaction mechanism of epoxidation of olefin by the [MnL?O₂??H₂O?]²⁺. This thesis includes the following parts:1. We reviewed the progresses about the research on metal-dioxygen complexes, including its classification, influencing factors of the geometric structures ?e.g. central metals and ligands? and reactivity, theoretical investigations on metal-dioxygen complexes and so on.2. We gave brief introduction for density functional theory, functional, basis set and the searching method of transition state, and introduction of some quantum chemistry softwares.3. We investigated three different binding modes ?bent end-on, linear end-on and side-on modes? of [MnL?O₂??H₂O?]²⁺. Water solvation effect was considered by combining an explicit water-cluster model and an implicit water solvation model. Influences of differently-sized calix[4]arene ligands were explored. The Mn-O₂ binding interaction of [MnL?O₂??H₂O?]²⁺ in different binding modes were discussed based on natural bond orbital ?NBO? calculation. A reasonable understanding on the experimentally proposed linear Mn-O-O unit was achieved. Our results will shed light on controllable synthesis of more end-on or more bent end-on Mn-dioxygen complexes through solvent polarity perturbations and ligand size adjustment.4. Two possible reaction mechanism of olefin epoxidation reaction with the [MnL?O₂??H₂O?]²⁺ were studied. One is that the dioxygen ligand of [MnL?O₂??H₂O?]²⁺ directly reacts with the olefins. The other is that the acyl radicals are firstly generated duing the activation of [MnL?O₂??H₂O?]²⁺ toward the isobutyraldehyde. Furthermore, the acyl radicals react with the oxygen to generate the acyl peroxy radicals and then olefins are oxidized. The calculated results show that the latter mechanism is more favorable. In addition, the manganese-oxygen complex ([MnL?O??H₂O?]²⁺) is more reactive than the manganese-dioxygen ([MnL?O₂??H₂O?]²⁺).