- Mo(CO)6/TBHP catalyzed autoxidation of 5-alkylidene-4,5-dihydrofurans
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Mo(CO)6/t-butyl hydroperoxide, well known to epoxidize olefins, was shown to be a mild and very efficient system for the autoxidation of 5- alkylidene-4,5-dihydrofurans. High yields of primary, secondary and tertiary furyl hydroperoxides have b
- Lattanzi, Alessandra,Lannece, Patrizia,Scettri, Arrigo
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- Pyrazolate-based cobalt(II)-containing metal-organic frameworks in heterogeneous catalytic oxidation reactions: Elucidating the role of entatic states for biomimetic oxidation processes
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Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active CoII centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O2 were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.
- Tonigold, Markus,Lu, Ying,Mavrandonakis, Andreas,Puls, Angela,Staudt, Reiner,Moellmer, Jens,Sauer, Joachim,Volkmer, Dirk
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supporting information; experimental part
p. 8671 - 8695
(2011/10/04)
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- Titanium tetra-tert-butoxide-tert-butyl hydroperoxide oxidizing system: Physicochemical and chemical aspects
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The reaction of titanium tetra-tert-butoxide with tert-butyl hydroperoxide (1: 2) (C6H6, 20 C) involves the steps of formation of the titanium-containing peroxide (t-BuO)3TiOOBu-t and peroxytrioxide (t-BuO)3TiOOOBu-t. The latter decomposes with the release of oxygen, often in the singlet form, and also homolytically with cleavage of both peroxy bonds. The corresponding alkoxy and peroxy radicals were identified by ESR using spin traps. The title system oxidizes organic substrates under mild conditions. Depending on the substrate structure, the active oxidant species can be titanium-containing peroxide, peroxytrioxide, and oxygen generated by the system.
- Stepovik,Gulenova,Martynova,Mar'Yasin,Cherkasov
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p. 266 - 276
(2008/09/20)
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- Oxidation of Phenols by Molecular Oxygen Catalysed by Transition Metal Complexes. Comparison between the Activity of Various Cobalt and Manganese Complexes and the Role of Peroxy Intermediates
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The oxidation reactions of hindered phenols by molecular oxygen catalysed by monomeric and polymeric cobalt-Schiff base complexes, cobalt and manganese porphyrins, and (pyridine)cobaloxime are described; the rate and selectivity of these reactions are very dependent on the catalyst and on the solvent.A new product has been isolated, 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienylperoxy(pyridine)cobaloxime, and was fully characterised by its elemental analysis and spectroscopic methods.The reactivity of peroxy compounds derived from 2,4,6-tri-t-butylphenol which are postulated as intermediates in the oxidation of this phenol has been studied.Thermal decomposition of 1,3,5-tri-t-butyl-4-oxocyclohexa-2,5-dienyl(pyridine)cobaloxime indicates that the formation of this complex from the phenol, O2, and (pyridine)cobaloxime(II) is reversible and that it is converted into 2,6-di-t-butyl-1,4-benzoquinone only in the presence of a proton source.The corresponding hydroperoxide is probably an intermediate in this transformation as its decomposition in the presence of the cobalt(II) or manganese(III) complexes yields the same final products as the overall oxidations.
- Frostin-Rio, Maryvonne,Pujol, Daniele,Bied-Charreton, Claude,Perree-Fauvet, Martine,Gaudemer, Alain
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p. 1971 - 1980
(2007/10/02)
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