- Mechanistically Driven Development of an Iron Catalyst for Selective Syn-Dihydroxylation of Alkenes with Aqueous Hydrogen Peroxide
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Product release is the rate-determining step in the arene syn-dihydroxylation reaction taking place at Rieske oxygenase enzymes and is regarded as a difficult problem to be resolved in the design of iron catalysts for olefin syn-dihydroxylation with potential utility in organic synthesis. Toward this end, in this work a novel catalyst bearing a sterically encumbered tetradentate ligand based in the tpa (tpa = tris(2-methylpyridyl)amine) scaffold, [FeII(CF3SO3)2(5-tips3tpa)], 1 has been designed. The steric demand of the ligand was envisioned as a key element to support a high catalytic activity by isolating the metal center, preventing bimolecular decomposition paths and facilitating product release. In synergistic combination with a Lewis acid that helps sequestering the product, 1 provides good to excellent yields of diol products (up to 97% isolated yield), in short reaction times under mild experimental conditions using a slight excess (1.5 equiv) of aqueous hydrogen peroxide, from the oxidation of a broad range of olefins. Predictable site selective syn-dihydroxylation of diolefins is shown. The encumbered nature of the ligand also provides a unique tool that has been used in combination with isotopic analysis to define the nature of the active species and the mechanism of activation of H2O2. Furthermore, 1 is shown to be a competent synthetic tool for preparing O-labeled diols using water as oxygen source.
- Borrell, Margarida,Costas, Miquel
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supporting information
p. 12821 - 12829
(2017/09/25)
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- Fe(PyTACN)-catalyzed cis-dihydroxylation of olefins with hydrogen peroxide
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A family of iron complexes with general formula [Fe(II)( R,Y,XPyTACN)(CF3SO3)2], where R,Y,XPyTACN=1-[2′-(4-Y-6-X-pyridyl)methyl]-4,7-dialkyl-1,4, 7-triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N-4 and N-7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis-dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(Me,Me,HPyTACN)(CF 3SO3)2] (7), was identified as the most efficient and selective cis-dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7, 2 equiv. of H2O2 as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis-dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn-diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe-catalyzed cis-dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron-deficient and aromatic olefins. Copyright
- Prat, Irene,Font, David,Company, Anna,Junge, Kathrin,Ribas, Xavi,Beller, Matthias,Costas, Miquel
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supporting information
p. 947 - 956
(2013/05/08)
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- Iron-catalyzed C-H hydroxylation and olefin cis-dihydroxylation using a single-electron oxidant and water as the oxygen-atom source
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Bioinspired oxidation: The hydroxylation of alkanes with retention of the configuration and the cis-dihydroxylation of olefins can be accomplished using [FeII(CF3SO3)2( Me,HPyTACN)] (1) as a catalyst, water as an oxygen-atom source, and cerium ammonium nitrate (CAN) as a single-electron oxidant. The oxidation of C-H bonds and C=C bonds, as well as water oxidation involves a common reaction intermediate formed by the reaction of CAN and [FeIV(O)(OH 2)(Me,HPyTACN)]+.
- Garcia-Bosch, Isaac,Codola, Zoel,Prat, Irene,Ribas, Xavi,Lloret-Fillol, Julio,Costas, Miquel
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supporting information
p. 13269 - 13273,5
(2012/12/12)
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- Olefin-dependent discrimination between two nonheme HO-Fev=O tautomeric species in catalytic H2O2 epoxidations
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A study was conducted to demonstrate olefin-dependent discrimination of two nonheme HO-Fev=O tautomeric species in catalytic H2O 2 epoxidations. Mechanistic studies were carried out under the condition of excess of olefin to minimize over-oxidation reactions and all reactions for the study were carried out under a N2 atmosphere to prevent auto-oxidation process due to presence of O2. It was observed that the diol/epoxide (D/E) ration for these reaction was dependent on the specific olefin and ranged from 3/2 (cyclooctene) to 6/1 (1-octene). The oxidation of cyclooctene using H218O2 revealed that only 28% of the oxygen atoms in the epoxide derived from H 2O2. Mechanistic results suggested that HO-Fe v=O oxidant need to be labeled before its reaction with substrates.
- Company, Anna,Feng, Yan,Gueell, Mireia,Ribas, Xavi,Luis, Josep M.,Que Jr., Lawrence,Costas, Miquel
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supporting information; experimental part
p. 3359 - 3362
(2009/12/06)
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- Ruthenium Tetroxide Oxidation of Alkenes. A More Complete Picture
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The ruthenium tetroxide oxidation of some linear and cyclic alkenes, representatives of five substitution patterns, has been performed in acetone-water (5:1) solution at -70 deg C using stoichiometric ammounts of the oxidant.The main reaction products are 1,2-diols and/or α-ketols depending on the nature of the substrate little amounts of scission products, aldehydes and/or carboxylic acids, are also obtained.Generally 1,2-diols predominate over α-ketols except in the oxidation of (-)-α-pinene that afforded the α-ketol in 51percent yield while no trace of the corresponding 1,2-diol was detected.All reactions prceeded through the formation of unstable brownish precipitates, presumably the intermediate ruthenium (VI) esters, which easily decomposed during the work-up step.Results from oxidation of trans-7-tetradecene and cis and trans-11-tetradecenyl acetate indicated that the reaction was syn stereospecific.In some cases, 1,3-dioxolane products, formed by condensation of the 1,2-diol and the aldehyde materials, were also obtained among the reaction products.Their possible origin is briefly discussed.
- Albarella, Laura,Piccialli, Vincenzo,Sica, Donato,Smaldone, Dina
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p. 2442 - 2456
(2007/10/03)
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- Electron-transfer Processes: Metal Salt Catalysed Oxidation of Olefins by Peroxydisulphate
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The reaction of simple olefins (oct-1-ene, oct-2-ene, cyclohexene, cycloheptene) with peroxydisulphate has been investigated under several conditions: (i) in aqueous medium and catalysis by AgI, FeII, and CuII; (ii) in acetic madium and catalysis by CuII, FeIII; (iii) in the presence of traps of nucleophilic alkyl radicals (protonated heteroaromatic bases and 1,4-benzoquinone either in water or in acetic acid).The catalyst and the radical trap govern the selectivity and allow a variety of new synthetic achievements.Evidence for a unified initial mechanism of electron transfer with formation of a radical cation from the olefin is reported to explain all the results.In water the radical cation gives a β-hydroxyalkyl radical, which, depending on the nature of the catalyst and the trap, can give the corresponding saturated alcohol by hydrogen abstraction, the products of CuII oxidation, or β-hydroxyalkylation of the heteroaromatic compound or 1,4-benzoquinone.In acetic acid the radical cation gives a β-acetoxyalkyl radical, which is oxidized to the corresponding allylic acetate by copper(II) acetate or trapped by the heteroaromatic base.
- Arnoldi, Claudio,Citterio, Attilio,Minisci, Francesco
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p. 531 - 542
(2007/10/02)
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