title: Temperature and pressure effects on C-H abstraction reactions involving compound I and II mimics in aqueous solution.
abstract: 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), Fe(III)(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 ΔH(‡) and ΔS(‡) to the free energy of activation (ΔG(‡)) 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 ΔH(‡) term in comparison to the -TΔS(‡) term to ΔG(‡) 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 (ΔV(‡)) for the oxidation of selected substrates by both reactive intermediates could be determined. Positive values of ΔV(‡) 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.
authors.affiliation: Faculty of Chemistry, Jagiellonian University , Ingardena 3, 30-060 Krakow, Poland.
authors.forename: Maria
authors.initials: M
authors.lastname: Oszajca
authors.forename: Alicja
authors.initials: A
authors.lastname: Franke
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Drzewiecka-Matuszek
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Brindell
authors.forename: Grażyna
authors.initials: G
authors.lastname: Stochel
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
mesh_terms: D002244:Carbon / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D018716:Molecular Mimicry; D011312:Pressure; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D002244:Carbon; D006859:Hydrogen