|M.Sc Student||Penias Navon Sharon|
|Subject||High Valent Iron Corroles, Characterization and Reactivity|
|Department||Department of Chemistry||Supervisor||Professor Zeev Gross|
|Full Thesis text - in Hebrew|
The research goals were to investigate oxidation reactions catalyzed by iron(III) corroles complexes, try to isolate new oxygen containing intermediates and to investigate if catalytic systems for aerobic oxidations of substrates may be designed.
Reactions between (tdcc)Fe and mCPBA were performed in both the absence and presence of styrene as to address the substrate effect on different elementary reactions. Spectral changes observed during the first second of the reaction were analyzed in terms of homolytic O-O cleavage of the peracid and generation of (tdcc)FeIV. Absence of ideal isosbestic points pointed toward the presence of a reaction intermediate, likely to be the coordination adduct of mCPBA to (tdcc)Fe. Kinetic investigations revealed that the observed reaction rate constants were affected by oxidant concentration, but not by the presence of styrene. A kinetic equation based on a steady state intermediate fitted the kinetic results. This data was analyzed in terms of a rapid equilibrium, followed by O-O bond cleavage as the rate limiting step.
At longer reaction times a significant influence of substrate was revealed. Without substrate, the Fe(IV) species was transformed in to a corrole p-cation radical species and partially bleached. Both phenomena were prevented in the presence of substrate.
The second part focused on comparing the catalytic activities of (tdcc)Fe and (tdcpp)Fe-Cl (an analogous porphyrin) in the oxidation of alkanes by ozone and by dioxygen. Catalytic ozonolysis of cumene yielded 2-phenyl-2-propanol as the major product, but acetophenone and cumene hydroperoxide were also formed. These results were analyzed in terms of two different pathways: alcohol via the "Rebound Mechanism" and peroxide, ketone (and some alcohol) via autoxidation. Higher catalyst concentrations increased product formation and selectivity to alcohol. Decreasing ozone flow improved the selectivity, but the amount of total products was lower.
Both catalysts ((tdcc)Fe and (tdcpp)Fe-Cl) did not catalyze aerobic oxidation of ethylbenzene at the checked reaction condition, while both did so for cumene. The product distribution profiles pointed toward two reaction mechanisms; autoxidation that yields primarly peroxide and another mechanism that yields mostly alcohol. The second mechanism was operative as long as the catalyst did not bleach, while autoxidation was relevant during all the reaction time.
This research addressed different aspects of oxidation reaction catalyzed by iron(III) corrole species, with mCPBA, ozone and dioxygen as oxidants. Reaction mechanisms were proposed based on spectral intermediates and other factors that influenced the reaction. The iron corrole was a poor catalyst for ozonolysis of alkanes but displayed better catalytic activity regarding aerobic oxidation.