ANION-RADICALS AS INTERMEDIATES IN THE CATHODIC REDUCTION OF BETA-DIKETOBORONATES (CYCLIC VOLTAMMETRY, EPR AND UV-VIS)

In beta-diketoboronates (2-R(1), 4-R(2)-C(3)HO(2)BX(2)), with R(1), R( 2), Me, Ph, substituted-Ph and Ph-CH=CH- and with 2X: C10H6O2 - -, C6H 4O2 - - , oxalate, 2AcO and fluorine 2F(-), an increase of the cyclovo ltammetric cathodic peal; potentials, E(pc), generally, to the negativ e values was observed for various substituents (R(1), R(2)): E(pe)(Me, Me) > (Me, Ph) > (Ph, Ph) > (Ph-CH=CH-, Ph-CH=CH-) and for various an ions (X): E(pc) (AcO, AcO) > (C6H4O2 - -) > (C10H6O2 - -) > (oxalate). The highest degree of reversibility in cyclic voltammetry and simulta neously stable anion radicals in EPR investigations were found if R(1) = R(2) = Ph, less for R(1) = Me, R(2) = Ph, irreversible and without anion radicals if R(1) = R(2) = Me, According to the analysis of EPR s pectra the anion radicals generated have a pi-character. Their spin di stribution of the unpaired electron was described by the following spl itting constants (expressed in mT): a(H)(CH3) = 0.4-0.7, phenyl proton s a(H)(m) congruent to 0.1, a(H)(o) congruent to 0.25, a(H)(P) congrue nt to 0.3, boron nucleus a(B)(11) = 0.04-0.1 and fluorine a(F) = 0.2-0 .4. A linear correlation between evaluated frequency (v(max)) from the longest wavelength absorption band and cathodic peak potentials (E(pc )) was found.