Temperature and Pressure Effects on C鈥揌 Abstraction Reactions Involving Compound I and II Mimics in Aqueous Solution
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- 作者：Maria Oszajca ; Alicja Franke ; Agnieszka Drzewiecka-Matuszek ; Ma艂gorzata Brindell ; Gra偶yna Stochel ; Rudi van Eldik
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：March 17, 2014
- 年：2014
- 卷：53
- 期：6
- 页码：2848-2857
- 全文大小：426K
- 年卷期：v.53,no.6(March 17, 2014)
- ISSN：1520-510X
文摘
The presented results cover a comparative mechanistic study on the reactivity of compound (Cpd) I and II mimics of a water-soluble iron(III) porphyrin, [meso-tetrakis(2,4,6-trimethyl-3-sulfonatophenyl)porphinato]iron(III), FeIII(TMPS). The acidity of the aqueous medium strongly controls the chemical nature and stability of the high-valent iron(IV) oxo species. Reactivity studies were performed at pH 5 and 10, where the Cpd I and II mimics are stabilized as the sole oxidizing species, respectively. The contributions of 螖H and 螖S to the free energy of activation (螖G) for the oxidation of 4-methoxybenzaldehyde (4-MB-ald), 4-methoxybenzyl alcohol (4-MB-alc), and 1-phenylethanol (1-PhEtOH) by the Cpd I and II mimics were determined. The relatively large contribution of the 螖H term in comparison to the 鈭?i>T螖S term to 螖G for reactions involving the Cpd II mimic indicates that the oxidation of selected substrates by this oxidizing species is clearly an enthalpy-controlled process. In contrast, different results were found for reactions with application of the Cpd I mimic. Depending on the nature of the substrate, the reaction at room temperature can be entropy-controlled, as found for the oxidation of 4-MB-alc, or enthalpy-controlled, as found for 1-PhEtOH. Importantly, for the first time, activation volumes (螖V) for the oxidation of selected substrates by both reactive intermediates could be determined. Positive values of 螖V were found for reactions with the Cpd II mimic and slightly negative ones for reactions with the Cpd II mimic. The results are discussed in the context of the oxidation mechanism conducted by the Cpd I and II mimics.