title: One-electron oxidation of ferrocenes by short-lived N-oxyl radicals. The role of structural effects on the intrinsic electron transfer reactivities.
abstract: A kinetic study of the one electron oxidation of substituted ferrocenes (FcX: X = H, COPh, COMe, CO(2)Et, CONH(2), CH(2)OH, Et, and Me(2)) by a series of N-oxyl radicals (succinimide-N-oxyl radical (SINO), maleimide-N-oxyl radical (MINO), 3-quinazolin-4-one-N-oxyl radical (QONO) and 3-benzotriazin-4-one-N-oxyl radical (BONO)), has been carried out in CH(3)CN. N-oxyl radicals were produced by hydrogen abstraction from the corresponding N-hydroxy derivatives by the cumyloxyl radical. With all systems, the rate constants exhibited a satisfactory fit to the Marcus equation allowing us to determine self-exchange reorganization energy values (λ(NO˙/NO(-))) which have been compared with those previously determined for the PINO/PINO(-) and BTNO/BTNO(-) couples. Even small modification of the structure of the N-oxyl radicals lead to significant variation of the λ(NO˙/NO(-)) values. The λ(NO˙/NO(-)) values increase in the order BONO < BTNO < QONO < PINO < SINO < MINO which do not parallel the order of the oxidation potentials. The higher λ(NO˙/NO(-)) values found for the MINO and SINO radicals might be in accordance with a lower degree of spin delocalization in the radicals MINO and SINO and charge delocalization in the anions MINO(-) and SINO(-) due to the absence of an aromatic ring in their structure.
authors.affiliation: Dipartimento di Chimica, Sapienza Università di Roma and Istituto CNR di Metodologie Chimiche (IMC-CNR), Sezione Meccanismi di Reazione, Rome, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Baciocchi
authors.forename: Massimo
authors.initials: M
authors.lastname: Bietti
authors.forename: Claudio
authors.initials: C
authors.lastname: D'Alfonso
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Lanzalunga
authors.forename: Andrea
authors.initials: A
authors.lastname: Lapi
authors.forename: Michela
authors.initials: M
authors.lastname: Salamone
mesh_terms: D003497:Cyclic N-Oxides / Q000737:chemistry*; D004579:Electron Transport; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D000075163:Metallocenes; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013237:Stereoisomerism
chemical_list: D003497:Cyclic N-Oxides; D005296:Ferrous Compounds; D005609:Free Radicals; D000075163:Metallocenes; C004998:ferrocene