Anion radicals as intermediates in the cathodic reduction of β-diketoboronates (cyclic voltammetry, EPR and uv—vis)
✍ Scribed by Peter Rapta; Katarína Erentová; Andrej Staško; Horst Hartmann
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 466 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
In fl-diketoboronates (2-R', 4R 2 -C3 H0 2 BX2 ), with R1, R 2 , Me, Ph, substituted-Ph and Ph-CH-CH-and with 2X : C 50H 60 2 --, C6H402 --, oxalate, 2AcO and fluorine 2F -, an increase of the cyclovoltammetric cathodic peak potentials, Ev ;, generally, to the negative values was observed for various substituents (R', R 2 ) : Ea(Me, Me) > (Me, Ph) > (Ph, Ph) > (Ph-CH~CH-, Ph-CH-C14-) and for various anions (X) : E,, (ACO, Aco) > (C 6 H4 02 --) > ( C 10 H 602 -H > (oxalate) . The highest degree of reversibility in cyclic voltammetry and simultaneously stable anion radicals in EPR investigations were found if R' = R 2 = Ph, less for R 2 = Me, R2 = Ph, irreversible and without anion radicals if R' = R 2 = Me. According to the analysis of EPR spectra the anion radicals generated have a ncharacter. Their spin distribution of the unpaired electron was described by the following splitting constants (expressed in mT) : aa(CH 2 ) = 0 .4-0.7, phenyl protons a" = 0.1, a,°, . 0.25, ax = 0.3, boron nucleus aa' = 0.04-0.1 and fluorine ar = 0.2-0.4 . A linear correlation between evaluated frequency (v,,) from the longest wavelength absorption band and cathodic peak potentials (E, 0) was found.