Synthesis and bioinorganic applications of manganese corrole and binuclear metallocorrole.

摘要

This thesis is concerned with the synthesis of novel corrole macrocycles and the applications of their metal complexes in mediating epoxidation reactions and hydrogen dismutation. Corrole is a porphyrin analogue capable of stabilizing high-valent metal ions. A series of cofacial biscorroles bearing various spacer groups have been synthesized. The dimanganese biscorroles were found to have a surprisingly high activity in catalyzing the dismutation of H2O 2 to give O2 and H2O, similar to the enzymatic reaction of catalase. An asymmetric Mn(III) Mn(V)-oxo transient intermediate was proposed to account for the elevated reactivity. A series of hetero binuclear biscorroles such as [Mn Al] and monomeric Mn(III) corroles equipped with an intramolecular proton donor were synthesized to show that the catalase-like reactivity may be associated with the presence of a Lewis acid and is consistent with a proton-assisted mechanism during the peroxide bond fission. Also synthesized was a series of sterically encumbered Mn-corroles in which both faces of the corrole ring are shielded to enhance the stability of the high-valent Mn(V)-oxo intermediate. Such Mn-corroles were capable of catalyzing epoxidation of olefins by an oxene-transfer reaction analogous to cytochrome P-450 chemistry. The shielding structure also provided a higher level of chemoselectivity in favor of the more exposed or less substituted double bond on the substrate. Furthermore, it was possible to isolate a relatively stable Mn(V)-oxo intermediate with a terphenyl-shielded corrole to permit resonance Raman study for the first time in solution at room temperature. The observed Mn(V)-O16 stretching frequency at 952cm-1 and that of Mn(V)-O 18 at 913 cm-1 could be interpreted in terms of a Mn(V)≡O triple bond. In another study, iron complexes of the sterically shielded corroles were prepared and the binding of such Fe-corroles to various ligands (such as chloride, nitrosyl and N-methylimidazole) were examined. Unfortunately, even with the sterically shielded structure in place, the iron corrole decomposed rapidly in the presence of PhIO or mCPBA oxidant, preventing further investigation of the high-valent intermediate. Finally, the reactivity of Mn-corrole imbedded in supermolecular hydrogel or organogel have been explored. The t-butyl hydroperoxide oxidation of various sulfides in the presence of the Mn-corrole in gel matrix was found to increase selectively the twice-oxidized sulfone at the expense of the less-oxidized sulfoxide, presumably due to diffusion phenomenon within the gel to alter the local concentration of reactants. Thus, the gel matrixes show promises to become a new platform for exploring biomimetic materials.