The development of an efficient, catalytically active, biomimetic model for cytochrome P-450 enzymes has been an area of intense research activity. Ruthenium porphyrin complexes have been the center of this research and have successfully been utilized, as catalysts, in major oxidation reactions such as the hydroxylation of alkanes, the epoxidation of alkenes and aromatic rings, and the N-oxidation of amines, among others. In this project, the kinetics of two-electron sulfoxidation of para-substituted phenyl methyl sulfides to the corresponding sulfoxides with well-characterized trans-dioxoruthenium(VI) porphyrin complexes were studied by rapid stopped-flow spectroscopy. The substituent effect in sulfides and in dioxoruthenium(VI) complexes were also kinetically investigated. The low-reactive trans-dioxoruthenium(VI) porphyrin complexes (3a-b) were synthesized from the oxidation of their carbonylruthenium(II) porphyrin precursors with m-chloroperoxybenzoic acid (m-CPBA) and characterized spectroscopically by 1H-NMR, IR, and UV-vis. The low-reactivity of these complexes makes them suitable for kinetic studies. The sulfoxidation with the trans-dioxoruthenium(VI) species followed a pseudo-first order kinetic decay from RuVI to RuIV species with no accumulation of intermediates. The reactivity order in the series of dioxoruthenium(VI) complexes follows 3b > 3a >3c, which is consistent with expectations based on the electrophilic nature of high-valent metal-oxo species. Steric effect of the substituents on the complexes also affected the reactivity order. The kinetic results revealed that the sulfoxidation reaction with these well-characterized dioxoruthenium(VI) complexes is 3 – 4 orders of magnitude faster than the epoxidation reaction with the same complexes under similar conditions.

Highly reactive transition metal-oxo intermediates are important active oxidant involved in numerous enzymes such as cytochrome P450 monooxygenases as well as in many useful metal-catalyzed oxidations. Many transition metal catalysts are designed for biomimetic studies of the predominant oxidation catalysts in Nature, the cytochrome P450 enzymes. In this work, a series of metalloporphyrin and metallocorrole complexes have been successfully synthesized and spectroscopically characterized by UV-vis, GCMS and 1H-NMR. The utilization of these complexes as catalysts for selective oxidation of sulfides and photocatalytic aerobic oxidations of activated hydrocarbons were investigated. Ruthenium(II) porphyrin complexes (2) and iron(III) corrole complexes (4) with iodobenzene diacetate [PhI(OAc)2] as a mild and excellent oxygen source efficiently catalyzed sulfides to sulfoxides under mild conditions. Ruthenium porphyrins (2) catalyzed the highly selective oxidation of para-substituted thioanisoles and allylic sulfides with PhI(OAc)2 in the presence of visible light. Over 95% conversion and 100% selectivity were achieved within 12 h. Results from competitive catalytic oxidations and spectra studies of the reaction of complexes (2) with PhI(OAc)2 in the absence of organic sulfide showed that the low-reactivity ruthenium(IV)-oxo intermediates (9) are most likely to be the active oxidant in the sulfoxidation reactions. An outstanding method for the highly selective oxidation of sulfides to sulfoxides was developed by using iron(III) corroles (4) and PhI(OAc)2 as mild oxygen source. Allylic thioanisoles and hydroxy sulfides could be successfully oxidized with good conversions and excellent selectivities within short time period. A significant accelerating effect on the rate of sulfoxidation reactions by small amount of water was noticed and will be understood by more studies. Fluorinated diiron(IV) μ-oxo biscorrole complex (5b) catalyzes alkenes and activated hydrocarbons using atmospheric oxygen and visible light (sunlight) with up to 1200 TONs. The observed photocatalytic oxidation is ascribed to a photodisproportionation mechanism to afford a highly reactive corrole-iron(V)-oxo species that can be directly observed by laser flash photolysis methods. It is noteworthy that the use of visible light (solar light) for activation of atmospheric oxygen without the consumption of a reducing agent in aforementioned photocatalysis is particularly relevant to realizing innovative and economically advantageous processes for conversion of hydrocarbons into oxygenates.