title: Dissociative electron transfer to diphenyl-substituted bicyclic endoperoxides: the effect of molecular structure on the reactivity of distonic radical anions and determination of thermochemical parameters.
abstract: The heterogeneous electron transfer reduction of the bicyclic endoperoxide 1,4-diphenyl-2,3-dioxabicyclo[2.2.1]hept-5-ene (4) was investigated in N,N-dimethylformamide at a glassy carbon electrode. The endoperoxide reacts by a concerted dissociative ET mechanism resulting in reduction of the O-O bond with an observed peak potential of -1.4 V at 0.2 V s-1. The major product (90% yield) resulting from the heterogeneous bulk electrolysis of 4 at -1.4 V with a rotating disk glassy carbon electrode is 1,4-diphenyl-cyclopent-2-ene-cis-1,3-diol with a consumption of 1.73 electrons per mole. In contrast, 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]oct-5-ene (1), undergoes a two-electron reduction mechanism in quantitative yield. This difference in product yield between 1 and 4 is suggestive of a radical-anion mechanism, as observed with 1,4-diphenyl-2,3-dioxabicyclo-[2.2.2] octane (2) and 1,4-diphenyl-2,3-dioxabicyclo[2.2.1]heptane (3). Convolution potential sweep voltammetry is used to determine unknown thermochemical parameters of 4, including the O-O bond dissociation energy and the standard reduction potential and a comparison is made to the previously studied bicyclic endoperoxides 1-3 with respect to the effect of molecular structure on the reactivity of distonic radical anions.
authors.affiliation: Department of Chemistry, University of Malta, Msida, MSD 2080, Malta. david.magri@um.edu.mt.
authors.forename: David C
authors.initials: DC
authors.lastname: Magri
authors.affiliation: Department of Chemistry, The University of Western Ontario, London, ON N6A 5B7, Canada. mworkent@uwo.ca.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Workentin
mesh_terms: D000838:Anions / Q000737:chemistry; D001713:Biphenyl Compounds / Q000737:chemistry*; D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D004126:Dimethylformamide / Q000737:chemistry; D004566:Electrodes; D004579:Electron Transport; D004583:Electrons; D007700:Kinetics; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010545:Peroxides / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D000838:Anions; D001713:Biphenyl Compounds; D001643:Bridged Bicyclo Compounds; D002244:Carbon; D004126:Dimethylformamide; D010545:Peroxides; C010574:biphenyl