title: Activation parameters for cyclohexene oxygenation by an oxoiron(IV) porphyrin pi-cation radical complex: entropy control of an allylic hydroxylation reaction.
abstract: Activation parameters for epoxidation and allylic hydroxylation reactions of cyclohexene with FeIVO(TMP)*+Cl (1) were determined. Within the experimental temperature range, the epoxidation reaction was enthalpy-controlled (i.e., DeltaH > -TDeltaS), while the allylic hydroxylation reaction was entropy-controlled (i.e., -TDeltaS > DeltaH). An unexpectedly large contribution of the entropy term for the allylic hydroxylation reaction indicated that the free energy of activation, DeltaG, rather than the activation energy, Ea, should be used to discuss the reaction mechanism and chemoselectivity. The results of this study bring caution to previous density functional theory studies, in which the reaction mechanism and chemoselectivity are evaluated from calculated Ea.
authors.affiliation: Institute for Molecular Science and Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, and Department of Functional Molecular Science, The Graduate University for Advanced Studies, Myodaiji, Okazaki, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takahashi
authors.forename: Takuya
authors.initials: T
authors.lastname: Kurahashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujii
mesh_terms: D015392:Chemistry, Inorganic / Q000379:methods*; D053138:Cyclohexenes / Q000737:chemistry*; D019277:Entropy; D006358:Hot Temperature; D007501:Iron / Q000737:chemistry; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics
chemical_list: D053138:Cyclohexenes; D011166:Porphyrins; D007501:Iron; D010100:Oxygen