| 1. |
- Jarenmark, Martin, et al.
(författare)
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A monocarboxylate-bridged diiron(III) mu-oxido complex that catalyzes alkane oxidation by hydrogen peroxide
- 2010
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1369-9261 .- 1144-0546. ; 34:10, s. 2118-2121
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of the ligand 2-(N-isopropyl-N-{(2-pyridyl)methyl}aminomethyl)- 6-(N-(carboxymethyl)-N-((2-pyridyl)-methyl) aminomethyl)- 4-methylphenol (H2IPCPMP) with two equivalents of Fe(ClO4)(2) and two equivalents of sodium pivalate in air leads to the formation of the mu-oxido, mu-carboxylato-bridged diiron complex [{Fe(H-IPCPMP)}(2)(mu-O)(Piv)]ClO4 (1) (Piv = pivalate). Complex 1 is capable of catalysing the oxidation of cyclohexane or 1,2-cis-dimethylcyclohexane by hydrogen peroxide, leading to the formation of the corresponding cyclohexanone and cyclohexanol, as well as a small amount of cyclohexyl hydroperoxide.
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| 2. |
- Mitra, Mainak, et al.
(författare)
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Catalytic C-H oxidations by nonheme mononuclear Fe(II) complexes of two pentadentate ligands: Evidence for an Fe(IV) oxo intermediate
- 2017
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Ingår i: Journal of Molecular Catalysis A: Chemical. - : Elsevier BV. - 1381-1169. ; 426, s. 350-356
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the Csingle bondH bond cleavage step, and resultant low kinetic isotope effect values. On the other hand, catalytic reactions performed using peracid media indicate the involvement of an oxidant different from the hydroxyl radical. For these reactions, the kinetic isotope effect values are relatively high (within a range of 4.2–5.1) and the C3/C2 selectivity parameters in adamantane oxidation are greater than 11, thereby excluding the presence of hydroxyl radicals in the Csingle bondH bond cleavage step. A low spin Fe(III)-OOH species has been detected in the H2O2-based catalytic system by UV/Vis, mass spectrometry and EPR spectroscopy, while an Fe(IV)-oxo species is postulated to be the active oxidant in the peracid-based catalytic systems. Computational studies on the Csingle bondH oxidation mechanism reveal that while the hydroxyl radical is mainly responsible for the H-atom abstraction in the H2O2-based catalytic system, it is the Fe(IV)-oxo species that abstracts the H-atom from the substrate in the peracid-based catalytic systems, in agreement with the experimental observations.
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| 3. |
- Mitra, Mainak, et al.
(författare)
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Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions
- 2015
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 54:15, s. 7152-7164
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Tidskriftsartikel (refereegranskat)abstract
- Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV–vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C–H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
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| 4. |
- Nilsson, Jessica, et al.
(författare)
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Salicylamide and salicylglycine oxidovanadium complexes with insulin-mimetic properties.
- 2011
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 1873-3344 .- 0162-0134. ; 105, s. 1795-1800
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of N-(2-hydroxybenzyl)-N-(2-picolyl) glycine (H(2)papy) with VOSO(4) in water gives the oxidovanadium(V) oxido-bridged dimer [{(papy)(VO)}(2) μ-O)] (1). Similarly, reaction of N-(2-hydroxybenzyl) glycine (H(2)glysal) with VOSO(4) gives [(glysal)VO(H(2)O)] (2) and reaction of salicylamide (Hsalam) with VOSO(4) in methanol gives [(salam)(2)VO] (3). The crystal structure of the oxido-bridged complex 1 is reported. The insulin-mimetic activity of all three complexes was evaluated with respect to their ability to phosphorylate protein kinase B (PKB). The speciations of complexes 1 and 2 were studied over the pH range 2-10. Complex 1 shows greater stability over the whole pH range but only 2 and 3 exhibit an insulin-mimetic effect.
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| 5. |
- Das, Biswanath, et al.
(författare)
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Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a mu-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor
- 2015
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1099-0682 .- 1434-1948. ; :21, s. 3590-3601
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Tidskriftsartikel (refereegranskat)abstract
- A new mu-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin2-ylmethyl)amino] propanoate (LiDPCPMPP), [Fe-2(mu-O)(LiDPCPMPP)(2)](ClO4)(2), has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h(-1)) and good activity in cyclohexene oxidation (TOF = 72 h(-1)) were detected. Partial retention of configuration (RC = 53%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3 degrees/2 degrees selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe-2(O)(O-2)-(LiDPCPMPP)(2)](2+), which might be an intermediate in the metal-based component of the oxidation process.
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