| 1. |
- Johansson, Adam Johannes, 1976-, et al.
(författare)
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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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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 34, s. 6741-6750
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Tidskriftsartikel (refereegranskat)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. |
- Noack, Holger, 1976-
(författare)
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Biomimetic Iron Complexes involved in Oxygenation and Chlorination : A Theoretical Study
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomimetic chemistry is directed towards the simulation of enzymatic reactivity with synthetic analogues. In this thesis a quantum chemical method has been employed to study the mechanism of highly reactive iron-oxo complexes involved in oxygenation and chlorination of organic substrates. The aim of this research is to gain greater understanding for the reactivity paradigm of the iron-oxo group. One reaction deals with the conversion of cyclohexane into adipic acid, a key chemical in industrial chemistry, catalyzed by an iron(II)-porphyrin complex in the presence of dioxygen. This process constitutes a ’green’ alternative to conventional adipic acid production, and is thus of great interest to synthetic chemistry. Another reaction investigated herein regards the selective chlorination observed for a new group of non-heme iron enzymes. With help of theoretical modeling it was possible to propose a mechanism that explains the observed selectivity. It is furthermore demonstrated how a biomimetic iron complex simulates the enzymatic reactivity by a different mechanism. Other topics covered in this thesis regard the structure-reactivity relationship of a binuclear iron complex and the intradiol C-C bond cleavage of catechol catalyzed by an iron(III) complex.
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| 3. |
- Noack, Holger, et al.
(författare)
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Theoretical Insights into Heme-Catalyzed Oxidation of Cyclohexane to Adipic Acid
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:4, s. 1194-1202
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Tidskriftsartikel (refereegranskat)abstract
- Adipic acid is a key compound in the chemical industry, where it is mainly used in the production of polymers. The conventional process of its generation requires vast amounts of energy and, moreover, produces environmentally deleterious substances. Thus, there is interest in alternative ways to gain adequate amounts of adipic acid. Experimental reports on a one-pot iron-catalyzed conversion of cyclohexane to adipic acid motivated a theoretical investigation based on density functional theory calculations. The process investigated is interesting because it requires less energy than contemporary methods and does not produce environmentally harmful side products. The aim of the present contribution is to gain insight into the mechanism of the iron-catalyzed cyclohexane conversion to provide a basis for the further development of this process. The rate-limiting step of the process is discussed, but considering the accuracy of the calculations, it is difficult to ensure whether the rate-limiting step is in the substrate oxidation or in the generation of the catalytically active species. It is shown that the slowest step in the substrate oxidation is the conversion of cyclohexanol to cyclohexane-1,2-diol. Hydrogen-atom transfer from one of the OH groups of cyclohexane-1,2-diol makes the intradiol cleavage occur spontaneously.
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