Design, synthesis and mechanistic studies of iron-TAML catalytic activators of hydrogen peroxide and a new activation chemistry of dioxygen by iron.

摘要

The Collins group has designed, synthesized, and characterized Fe(III)-tetraamido macrocycle (Fe(III)-TAML) catalysts capable of activating hydrogen peroxide for technologically prevalent oxidation chemistry. As discussed in Chapter 2, a new synthetic method has been developed resulting in higher yields, time savings, less environmental impact, and a more economical process.; Chapter 3 describes the chemistry of various Fe(III)-TAML catalysts in aqueous solution. Detailed kinetic studies of the acid-induced demetallation of Fe(III)-TAMLs, their speciation and acid-base equilibria, and binding by anionic ligands such as chloride have been performed using several spectroscopic methods such as EPR, UV/Vis and X-ray crystallography.; Chapter 4 describes a detailed kinetic and mechanistic investigation of the catalase and peroxidase like activity of Fe(III)-TAMLs. The objectives of this study include, understanding the major kinetic features of catalysis by the Fe(III)-TAML activators; estimation of the absolute reactivity of the Fe(III)-TAML activators in order to compare their activity to the relevant catalase and peroxidase enzymes, and to more fully understand the little known catalytic mechanism of the catalase-peroxidase enzymes by studying Fe(III)-TAML activators as their functioning mimetics.; Chapter 5 describes our recent advancements towards the potential activation of dioxygen by Fe(III)-TAMLs. The 5-coordinated tetraphenylphosphonium salts of electron-rich Fe(III)-TAML complexes with an axial aqua ligand react rapidly with O2, under ambient conditions in methylene chloride, or other weakly coordinating solvents, to render mu-oxo-bridged diiron(IV) complexes (2). Isotopic labeling experiments with 18O 2 and H218O have established that the bridging oxygen atom of 2 derives from an O2 molecule. Autoxidation was shown not to be involved in the formation of 2.; Chapter 6 summarizes our initial efforts in the application of Fe(III)-TAMLs for green syntheses such as hydrocarbon hydroxylation and epoxidation of alkenes. The results indicate that Fe(III)-TAMLs are capable of hydroxylating benzene and toluene, along with epoxidize alkenes like styrene, stilbene, and cyclooctene. These results also indicate that the electronic properties of the Fe(III)-TAMLs may play a significant role in controlling the reactivity and selectivity of substrate oxidation. Therefore, various Fe(III)-TAML activators, containing electron-withdrawing and electron-releasing groups, should be tested to achieve higher yields under optimized experimental conditions. (Abstract shortened by UMI.)