High-valent manganese complexes of porphyrin and corrole: Kinetics and spin-state dependence of hydrogen atom transfer reactions
Abstract
Metalloporphyrins play a vital role at the active sites of certain enzymes that facilitate several critical processes. Synthetic metallporphyrins and their analogs serve as biomimetic reagents used to gain insight into the complex mechanistic details of enzymatic reactions, as well as proving to be useful catalysts in a variety of organic synthesis reactions. Manganese tetrakis(pentafluorophenyl)porphyrin complexes were synthesized in various oxidation states with different axial ligands. A manganese(III) acetate tetrakis(pentafluorophenyl)porphyrin complex, (tpfpp)MnIII (OAc), and a manganese(II) tetrakis(pentafluorophenyl)porphyrin complex, (tpfpp)MnII(THF)2, showed potential as aziridination catalysts in initial reactivity studies. The reactivity of the high-valent manganese(V) imido corrole (tpfc)MnV(NTs) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole and Ts = p-tolunenesulfonyl) with respect to hydrogen atom donor substrates was investigated using a series of para-substituted 2,6-di- tert-butylphenols. The general reaction between (tpfc)MnV (NTs) and substituted phenols yields (tpfc)MnIII, H 2NTs, and the corresponding phenoxyl radicals. A Hammett plot consists of a V-shape with a negative ρ for electron-donating substituents and a positive ñ for electron-withdrawing substituents. The mechanism for electron-donating substituents consists of a concerted proton-electron transfer; however, the mechanism for electron-withdrawing substitutents is proton-transfer followed by electron-transfer. The reactivity of high-valent manganese imido corrole complexes displays spin-state dependence with respect to hydrogen atom transfer reactions. The high-spin complex (tpfc)Mn(NTs) was shown to successfully oxidize 2,4,6-tri- tert-butylphenol, whereas the low-spin complex (tpfc)Mn(NArCl 2) (ArCl2 = 2,6-Cl2C6H3) does not oxidize 2,4,6-tri-tert-butylphenol substrate. However, the addition of trifluoroacetic acid to (tpfc)Mn(NArCl2) and 2,4,6-tri- tert-butylphenol causes the reaction to proceed. Biomimetic chlorite dismutation investigations were performed with several different synthetic metalloporphyrinoid complexes. The manganese water-soluble porphyrin complex (TF4TMAP)Mn (TF4TMAP = 5,10,15,20-tetrakis(tetrafluoro-N,N,N-trimethylanilinium)porphyrinatio) was found to decompose chlorite to chlorine dioxide (ClO2).
Degree
Ph.D.
Advisors
Abu-Omar, Purdue University.
Subject Area
Inorganic chemistry
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