- Reductive Activation of O2 by Non-Heme Iron(II) Benzilate Complexes of N4 Ligands: Effect of Ligand Topology on the Reactivity of O2-Derived Oxidant
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A series of iron(II) benzilate complexes (1-7) with general formula [(L)FeII(benzilate)]+ have been isolated and characterized to study the effect of supporting ligand (L) on the reactivity of metal-based oxidant generated in the reaction with dioxygen. Five tripodal N4 ligands (tris(2-pyridylmethyl)amine (TPA in 1), tris(6-methyl-2-pyridylmethyl)amine (6-Me3-TPA in 2), N1,N1-dimethyl-N2,N2-bis(2-pyridylmethyl)ethane-1,2-diamine (iso-BPMEN in 3), N1,N1-dimethyl-N2,N2-bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine (6-Me2-iso-BPMEN in 4), and tris(2-benzimidazolylmethyl)amine (TBimA in 7)) along with two linear tetradentate amine ligands (N1,N2-dimethyl-N1,N2-bis(2-pyridylmethyl)ethane-1,2-diamine (BPMEN in 5) and N1,N2-dimethyl-N1,N2-bis(6-methyl-2-pyridylmethyl)ethane-1,2-diamine (6-Me2-BPMEN in 6)) were employed in the study. Single-crystal X-ray structural studies reveal that each of the complex cations of 1-3 and 5 contains a mononuclear six-coordinate iron(II) center coordinated by a monoanionic benzilate, whereas complex 7 contains a mononuclear five-coordinate iron(II) center. Benzilate binds to the iron center in a monodentate fashion via one of the carboxylate oxygens in 1 and 7, but it coordinates in a bidentate chelating mode through carboxylate oxygen and neutral hydroxy oxygen in 2, 3, and 5. All of the iron(II) complexes react with dioxygen to exhibit quantitative decarboxylation of benzilic acid to benzophenone. In the decarboxylation pathway, dioxygen becomes reduced on the iron center and the resulting iron-oxygen oxidant shows versatile reactivity. The oxidants are nucleophilic in nature and oxidize sulfide to sulfoxide and sulfone. Furthermore, complexes 2 and 4-6 react with alkenes to produce cis-diols in moderate yields with the incorporation of both the oxygen atoms of dioxygen. The oxygen atoms of the nucleophilic oxidants do not exchange with water. On the basis of interception studies, nucleophilic iron(II) hydroperoxides are proposed to generate in situ in the reaction pathways. The difference in reactivity of the complexes toward external substrates could be attributed to the geometry of the O2-derived iron-oxygen oxidant. DFT calculations suggest that, among all possible geometries and spin states, high-spin side-on iron(II) hydroperoxides are energetically favorable for the complexes of 6-Me3-TPA, 6-Me2-iso-BPMEN, BPMEN, and 6-Me2-BPMEN ligands, while high spin end-on iron(II) hydroperoxides are favorable for the complexes of TPA, iso-BPMEN, and TBimA ligands.
- Chakraborty, Biswarup,Jana, Rahul Dev,Singh, Reena,Paria, Sayantan,Paine, Tapan Kanti
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p. 359 - 371
(2017/01/13)
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- 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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- Transfer hydrogenation employing ethylene diamine bisborane in water and Pd- and ru-nanoparticles in ionic liquids
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Herein we demonstrate the use of ethylenediamine bisborane (EDAB) as a suitable hydrogen source for transfer hydrogenation reactions on C-C double bonds mediated by metal nanoparticles. Moreover, EDAB also acts as a reducing agent for carbonyl functionalities in water under metal-free conditions.
- Sahler, Sebastian,Scott, Martin,Gedig, Christian,Prechtl, Martin H.G.
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p. 17058 - 17069
(2015/12/01)
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- Rabbit 3-hydroxyhexobarbital dehydrogenase is a NADPH-preferring reductase with broad substrate specificity for ketosteroids, prostaglandin D2, and other endogenous and xenobiotic carbonyl compounds
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3-Hydroxyhexobarbital dehydrogenase (3HBD) catalyzes NAD(P) +-linked oxidation of 3-hydroxyhexobarbital into 3-oxohexobarbital. The enzyme has been thought to act as a dehydrogenase for xenobiotic alcohols and some hydroxysteroids, but its physiological function remains unknown. We have purified rabbit 3HBD, isolated its cDNA, and examined its specificity for coenzymes and substrates, reaction directionality and tissue distribution. 3HBD is a member (AKR1C29) of the aldo-keto reductase (AKR) superfamily, and exhibited high preference for NADP(H) over NAD(H) at a physiological pH of 7.4. In the NADPH-linked reduction, 3HBD showed broad substrate specificity for a variety of quinones, ketones and aldehydes, including 3-, 17- and 20-ketosteroids and prostaglandin D2, which were converted to 3α-, 17β- and 20α-hydroxysteroids and 9α,11β- prostaglandin F2, respectively. Especially, α-diketones (such as isatin and diacetyl) and lipid peroxidation-derived aldehydes (such as 4-oxo- and 4-hydroxy-2-nonenals) were excellent substrates showing low Km values (0.1-5.9 μM). In 3HBD-overexpressed cells, 3-oxohexobarbital and 5β-androstan-3α-ol-17-one were metabolized into 3-hydroxyhexobarbital and 5β-androstane-3α,17β-diol, respectively, but the reverse reactions did not proceed. The overexpression of the enzyme in the cells decreased the cytotoxicity of 4-oxo-2-nonenal. The mRNA for 3HBD was ubiquitously expressed in rabbit tissues. The results suggest that 3HBD is an NADPH-preferring reductase, and plays roles in the metabolisms of steroids, prostaglandin D2, carbohydrates and xenobiotics, as well as a defense system, protecting against reactive carbonyl compounds.
- Endo, Satoshi,Matsunaga, Toshiyuki,Matsumoto, Atsuko,Arai, Yuki,Ohno, Satoshi,El-Kabbani, Ossama,Tajima, Kazuo,Bunai, Yasuo,Yamano, Shigeru,Hara, Akira,Kitade, Yukio
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p. 1366 - 1375
(2013/11/19)
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- Iron-catalyzed asymmetric olefin cis-dihydroxylation with 97% enantiomeric excess
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Big cis-ster: The use of an (R,R)-bipyrrolidine backbone with two α-methylpyridine pendant arms affords a tetradentate N4 ligand that coordinates an iron center with cis-α topology (see picture; Fe purple, C gray, N blue, O red, S yellow, F green). This complex catalyzes the reaction between H2O2 and cis-2-heptene to afford a cis-diol product in very high enantioselectivity. (Figure Presented)
- Suzuki, Ken,Oldenburg, Paul D.,Que Jr., Lawrence
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p. 1887 - 1889
(2008/12/22)
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- Ligand topology effects on olefin oxidations by bio-inspired [Fe II(N2Py2)] catalysts
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Linear tetradentate N2Py2 ligands can coordinate to an octahedral FeII center in three possible topologies (cis-α, cis-β, and trans). While for the N,N'-bis(2-pyridylmethyl)-l,2- diaminoethane (bpmen) complex, only the cis-α topology has been observed, for N,N'-bis(2-pyridylmethyl)-1,2-diamino-cyclohexane (bpmcn) both cis-α and cis-β isomers have been reported. To date, no facile interconversion between cis-α and cis-β topologies has been observed for iron(II) complexes even at high temperatures. However, this work provides evidence for facile interconversion in solution of cis-α, cis-β, and trans topologies for [Fe(bpmpn)X2] (bpmpn = N, N'-bis(2-pyridylmethyl)-1,3- diaminopropane; X = triflate, CH3CN) complexes. As reported previously, the catalytic behavior of cis-α and cis-β isomers of [Fe(bpmcn)(OTf)2] with respect to olefin oxidation depends dramatically on the geometry adopted by the iron complex. To establish a general pattern of the catalysis/ topology dependence, this work presents an extended comparison of the catalytic behavior for oxidation of olefins of a family of [Fe(N2py2)] complexes that present different topologies. 18O labeling experiments provide evidence for a complex mechanistic land-scape in which several pathways should be considered. Complexes with a trans topology catalyze only non-water-assisted epoxidation. In contrast, complexes with a cis-α topology, such as [Fe(bpmen)X2] and [Fe(α-bpmcn)-(OTf)2], can catalyze both epoxidation and cis-dihydroxylation through a water-assisted mechanism. Surprisingly, [Fe(bpmpn)X2] and [Fe(β-bpmcn)-(OTf)2] catalyze epoxidation via a water-assisted pathway and cis-dihydroxylation via a non-water-assisted mechanism, a result that requires two independent and distinct oxidants.
- Mas-Balleste, Ruben,Costas, Miquel,Van Den Berg, Tieme,Que Jr., Lawrence
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p. 7489 - 7500
(2007/10/03)
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- Enantioselective microbial hydrolysis of dissymmetrical cyclic carbonates with disubstitution
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Enantioselective microbial hydrolysis of C1 and C2 dissymmetrical cyclic carbonates with disubstitution (methyl and another groups) has been developed. Pseudomonas diminuta (FU0090), a bacterium, efficiently catalyzes the hydrolysis of five-membered cyclic carbonates. While the trans-substrates are hydrolyzed with low enantioselectivities and/or reactivities, the microbe hydrolyzes the cis-substrates with very high enantioselectivities to afford the corresponding almost optically pure anti-(2R,3S)-diols. On the other hand, six-membered trans-cyclic carbonates are enantioselectively hydrolyzed to afford the corresponding optically active syn-(2R,4R)-diols, although the hydrolysis of the cis-substrates gives racemic compounds. In all cases, the enzyme prefers the (R)-enantiomer for the carbon atom bearing a methyl group.
- Nogawa, Masaki,Sugawara, Satomi,Iizuka, Rie,Shimojo, Megumi,Ohta, Hiromichi,Hatanaka, Minoru,Matsumoto, Kazutsugu
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p. 12071 - 12083
(2007/10/03)
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- NOVEL PROCESS FOR PRODUCING 1,2-DIOL
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A process for producing a 1,2-diol through the reaction of an olefin with hydrogen peroxide. The process is highly efficient and highly selective and catalyst recovery and reuse are easy. It does not use any strong acid or strong base causative of apparatus corrosion. The process for producing a 1,2-diol is characterized by reacting an olefin with hydrogen peroxide in the presence of a polymer having a sulfo group.
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- The Os/Cu-Al-hydrotalcite catalysed hydroxylation of alkenes
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A new Os/Cu-Al-hydrotalcite-like catalyst is described which, with N-methylmorpholine oxide as co-oxidant, heterogeneously catalyses the hydroxylation of olefins to give diols selectively and in high yield.
- Friedrich, Holger B.,Govender, Mayashree,Makhoba, Xolani,Ngcobo, T. Dennis,Onani, Martin O.
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p. 2922 - 2923
(2007/10/03)
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- Iron-catalyzed olefin cis-dihydroxylation by H2O2: Electrophilic versus nucleophilic mechanisms
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Previous studies have classified a series of nonheme iron catalysts for olefin cis-dihydroxylation by H2O2 into two groups. Complex 1, [(TPA)Fe(OTf)2], representative of Class A catalysts, forms a low-spin FeIII-OOH intermediate that gives rise to a high-valent FeV(=O)OH oxidant. The preference of this catalyst for electron-rich olefins demonstrates its electrophilic character. On the other hand, complex 2, [(6-Me3-TPA)Fe(OTf)2], representative of Class B catalysts, prefers instead to oxidize electron-deficient olefins, suggesting an oxidant with nucleophilic character. It is suggested that such a nucleophilic oxidant may be the high-spin FeIII-OOH intermediate derived from 2 or the FeIV(=O)(?OH) species derived therefrom. Copyright
- Fujita, Megumi,Costas, Miquel,Que Jr., Lawrence
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p. 9912 - 9913
(2007/10/03)
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- High conversion of olefins to cis-diols by non-heme iron catalysts and H2O2.
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Efficient and highly stereoselective oxidation of olefins to cis-diols as the major product is obtained by using biomimetic non-heme FeII catalysts in combination with H2O2.
- Ryu, Ju Yeon,Kim, Jinheung,Costas, Miquel,Chen, Kui,Nam, Wonwoo,Que Jr., Lawrence
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p. 1288 - 1289
(2007/10/03)
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