Olefin Epoxidation by Alkyl Hydroperoxide with a Novel Cross-Bridged Cyclam Manganese Complex: Demonstration of Oxygenation by Two Distinct Reactive Intermediates
- 13 February 2007
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 46 (6), 2173-2180
- https://doi.org/10.1021/ic061957r
Abstract
Olefin epoxidation provides an operative protocol to investigate the oxygen transfer process in nature. A novel manganese complex with a cross-bridged cyclam ligand, MnIV(Me2EBC)(OH)2(2+) (Me2EBC = 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane), was used to study the epoxidation mechanism with biologically important oxidants, alkyl hydroperoxides. Results from direct reaction of the freshly synthesized manganese(IV) complex, [Mn(Me2EBC)(OH)2](PF6)2, with various olefins in neutral or basic solution, and from catalytic epoxidation with oxygen-labeled solvent, H2 18O, eliminate the manganese oxo moiety, Mn(IV)=O, as the reactive intermediate and obviate an oxygen rebound mechanism. Epoxidations of norbornylene under different conditions indicate multiple mechanisms for epoxidation, and cis-stilbene epoxidation under atmospheric 18O2 reveals a product distribution indicating at least two distinctive intermediates serving as the reactive species for epoxidation. In addition to alkyl peroxide radicals as dominant intermediates, an alkyl hydroperoxide adduct of high oxidation state manganese(IV) is suggested as the third kind of active intermediate responsible for epoxidation. This third intermediate functions by the Lewis acid pathway, a process best known for hydrogen peroxide adducts. Furthermore, the tert-butyl peroxide adduct of this manganese(IV) complex was detected by mass spectroscopy under catalytic oxidation conditions.Keywords
This publication has 55 references indexed in Scilit:
- Olefin Epoxidation by the Hydrogen Peroxide Adduct of a Novel Non-heme Mangangese(IV) Complex: Demonstration of Oxygen Transfer by Multiple MechanismsInorganic Chemistry, 2006
- Experimental Evidence for Multiple Oxidation Pathways in the (salen)Mn-Catalyzed Epoxidation of AlkenesChemistry – A European Journal, 2002
- cis-Stilbene and (1α,2β,3α)-(2-Ethenyl-3-methoxycyclopropyl)benzene as Mechanistic Probes in the MnIII(salen)-Catalyzed Epoxidation: Influence of the Oxygen Source and the Counterion on the Diastereoselectivity of the Competitive Concerted and Radical-Type Oxygen TransferJournal of the American Chemical Society, 2002
- The First Olefin‐Substituted Peroxomolybdenum Complex: Insight into a New Mechanism for the Molybdenum‐Catalyzed Epoxidation of OlefinsAngewandte Chemie-International Edition, 1995
- Air Oxidation of a Five-Coordinate Mn(III) Dimer to a High-Valent Oxomanganese(V) ComplexJournal of the American Chemical Society, 1994
- Nature of the epoxidizing species generated by reaction of alkyl hydroperoxides with iron(III) porphyrins. Oxidations of cis-stilbene and (Z)-1,2-bis(trans-2, trans-3-diphenylcyclopropyl)ethene by tert-BuOOH in the presence of [meso-tetrakis(2,4,6-trimethylphenyl)porphinato]-, [meso-tetrakis(2,6-dichlorophenyl)porphinato]-, and [meso-tetrakis(2,6-dibromophenyl)porphinato]iron(III) chlorideJournal of the American Chemical Society, 1991
- A water-stable manganese(V)-oxo complex: definitive assignment of a .nu.Mnv.tplbond.O infrared vibrationJournal of the American Chemical Society, 1990
- Oxygenation of organic substrates by iodosylbenzene catalyzed by soluble manganese, iron, cobalt, or copper salts in acetonitrileInorganic Chemistry, 1984
- In the presence of imidazole, iron-and manganese-porphyrins catalyse the epoxidation of alkenes by alkyl hydroperoxidesJournal of the Chemical Society, Chemical Communications, 1984
- The Origin of Epoxides in the Liquid Phase Oxidation of Olefins with Molecular OxygenJournal of the American Chemical Society, 1963