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- Johansson, Adam Johannes, 1976-, et al.
(author)
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Observed enhancement of the reactivity of a biomimetic diiron complex by the addition of water - mechanistic insights from theoretical modeling
- 2009
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In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 34, s. 6741-6750
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Journal article (peer-reviewed)abstract
- The biomimetic diiron complex [FeIIIFeIV(m-O)2(5-Me3-TPA)2](ClO4)3 (TPA = tris(2- pyridylmethyl)amine) has been found to be capable of oxidizing 9,10-dihydroanthracene in a solution of acetonitrile. Addition of water up to 1 M makes the reaction 200 times faster, suggesting that the water molecule in some way activates the catalyst for more efficient substrate oxidation. It is proposed that the enhanced reactivity results from the coordination of a water molecule to the iron(III) half of the complex, converting the bis-m-oxo structure of the diiron complex to a ring-opened form where one of the bridging oxo groups is transformed into a terminal oxo group on iron(IV). The suggested mechanism is supported by DFT (B3LYP) calculations and transition state theory. Two different computational models of the diiron complex are used to model the hydroxylation of cyclohexane to cyclohexanol. Model 1 has a bis-m-oxo diiron core (diamond core) while model 2 represents the “open core” analogue with one bridging m-oxo group, a terminal oxo ligand on iron(IV), and a water molecule coordinated to iron(III). The computational results clearly suggest that the terminal oxo group is more reactive than the bridging oxo group. The free energy of activation is 7.0 kcal mol-1 lower for the rate limiting step when the oxidant has a terminal oxo group than when both oxo groups are bridging the irons.
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| 2. |
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| 3. |
- Noack, Holger, et al.
(author)
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Theoretical investigation on the oxidative chlorination performed by a biomimetic non-heme iron catalyst
- 2007
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In: Journal of Biological Inorganic Chemistry. - 0949-8257 .- 1432-1327. ; 12, s. 1151-1162
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Journal article (peer-reviewed)abstract
- The present study is a part of an effort to understand the mechanism of the oxidative chlorination, as performed by a biomimetic non-heme iron complex. This catalytically active complex is generated from a peroxide and [(TPA)FeIIICl2]+ [TPA is tris(2-pyridylmethyl)amine]. The reaction catalyzed by [(TPA)FeCl2]+/ROOH involves either [(TPA)ClFeV=O]2+ or [(TPA)ClFeIV=O]+ as an intermediate. On the basis of density functional theory the reaction of these two possible catalysts with cyclohexane is investigated. A question addressed is how the competing hydroxylation of the substrate is avoided. It is demon- strated that the high-valent iron complex [(TPA)Cl– FeV=O]2+ is capable of stereospecific alkane chlorination, based on an ionic rather than on a radical pathway. In contrast, the results found for [(TPA)ClFeIV=O]+ cannot explain the experimental findings. In this case the transition states for chlorination and hydroxylation are energetically too close. The exclusive chlorination of the substrate by Cl–FeIV=O may be explained by an indirect or a direct effect, altering the position of the competing rebound barriers.
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