Synthesis, Kinetic and Photocatalytic Studies of Porphyrin-Ruthenium-Oxo Complexes

Macrocyclic ligand-complexed transition metal-oxo intermediates are the active oxidizing species in a variety of important biological and catalytic oxidation reactions. Many transition metal catalysts have been designed to mimic the predominant oxidation catalysts in Nature, namely the cytochrome P450 enzymes. Ruthenium porphyrin complexes have been the center of the research and have successfully been utilized, as catalysts, in major oxidation reactions such as the hydroxylation of alkanes. This study focuses on kinetic and photocatalytic studies of oxidation reactions with wellcharacterized high-valent ruthenium-oxo porphyrin complexes. <br> The <i>trans</i>-dioxoruthenium(VI) porphyrins have been among the best characterized metal-oxo intermediates and their involvement as the active oxidant in the hydrocarbon oxidation have been extensively studied. Following the literature known methods, a series of <i>trans</i>-dioxoruthenium(VI) porphyrin complexes <b>(3a-b)</b> were synthesized and spectroscopically characterized by UV-vis, IR and lH-NMR. In addition to the well-known chemical methods, we developed a novel photochemical approach for generation of <i>trans</i>-dioxoruthenium(VI) porphyrins with visible light. The fast kinetic study of two-electron oxidations of <i>para</i>-substituted phenyl methyl sulfides by these dioxoruthenium(VI) species was conducted by using stopped-flow spectroscopy. Results showed that the decay of <i>trans</i>--dioxoruthenium(VI) porphyrins in the presence of reactive sulfides follows a biexponential process. The reactivity order in the series of dioxoruthenium complexes follows TPFPP> TPP> TMP, consistent with expectations based on the electrophilic nature of high-valent metal-oxo species. Moreover, the sulfoxidation reactions are 3 to 4 orders of magnitude faster than the well-known epoxidation reactions. In addition, several ruthenium porphyrins were used as the catalysts in the competitive oxidation reactions to identify the kinetically competent oxidants during catalytic turnover conditions. <br> The photocatalytic studies of aerobic oxidation reactions of hydrocarbons catalyzed by a bis-porphyrin-ruthenium(lV) fl-OXO dimer using atmospheric oxygen as oxygen source in the absence of co-reductants were investigated as well. The ruthenium(lV) fl-OXO bisporphyrin <b>(6a)</b> was found to catalyze aerobic oxidation of a variety of organic substrates efficiently. By comparison, <b>6a</b> was found to be more efficient photocatalyst than the well-known <b>3a</b> under identical conditions. A KIE at 298K was found to be larger than those observed in autoxidation processes, suggesting a nonradical mechanism that involved the intermediacy of ruthenium(V)-oxo species as postulated.

Name thesis:degree_name

Master of Science in Chemistry

Discipline thesis:degree_discipline

Department of Chemistry

Year

2010

Author dc:creator

• Huang, Yan

Contributors dc:contributor

• Dr. Rui Zhang (Director), Dr. Kevin Williams, Dr. Bangbo Yan

• catalysis
• oxidation
• bioinorganic chemistry
• transition metal compounds
• catalytic oxidation
• Biotechnology
• Environmental Chemistry
• Organic Chemistry
• Other Biochemistry, Biophysics, and Structural Biology

Repository record dc:identifier

https://digitalcommons.wku.edu/theses/182

OAI identifier oai:identifier

oai:digitalcommons.wku.edu:theses-1184