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Remarkable Solvent, Porphyrin Ligand, and Substrate Effects on Participation of Multiple Active Oxidants in Manganese(III) Porphyrin Catalyzed Oxidation Reactions
Author(s) -
Hyun Min Young,
Jo Young Dan,
Lee Jun Ho,
Lee Hong Gyu,
Park Hyun Min,
Hwang In Hong,
Kim Kyeong Beom,
Lee Suk Joong,
Kim Cheal
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202640
Subject(s) - heterolysis , homolysis , chemistry , porphyrin , cyclohexene , ethylbenzene , catalysis , photochemistry , solvent , medicinal chemistry , ligand (biochemistry) , toluene , substrate (aquarium) , manganese , organic chemistry , radical , biochemistry , oceanography , receptor , geology
The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron‐withdrawing and ‐donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1‐octene, and ethylbenzene in various solvent systems, namely, toluene, CH 2 Cl 2 , CH 3 CN, and H 2 O/CH 3 CN (1:4). With an increase in the concentration of the easy‐to‐oxidize substrate cyclohexene in the presence of [(TMP)MnCl] ( 1 a ) with electron‐donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)MnOOC(O)R] species 2 a is the major active species. When the substrate was changed from the easy‐to‐oxidize one (cyclohexene) to difficult‐to‐oxidize ones (1‐octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F 20 TPP)MnOOC(O)R] species 2 b generated from the reaction of [(F 20 TPP)MnCl] ( 1 b ) with electron‐withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)MnOOR] 2 a ) depending on the concentration of the easy‐to‐oxidize substrate cyclohexene in all aprotic solvent systems except for CH 3 CN, whereas Mn V O species is the major active oxidant in the protic solvent system. With difficult‐to‐oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1‐octene in toluene, indicating that a Mn V O intermediate generated from the heterolytic cleavage of 2 b becomes a major reactive species. We also studied the competitive epoxidations of cis ‐2‐octene and trans ‐2‐octene with two manganese(III) porphyrin complexes by meta ‐chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis ‐ to trans ‐2‐octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.