α-Linked Bifuran and α,α‘-Linked Tricycles Containing Furan and/or Thiophene. EPR Investigations and Electrochemical Behavior

Abstract

The radical cations from 5,5‘-dimethyl-2,2‘-bifuran (1) and 5,5‘‘-dimethyl-2,2‘,5‘,2‘‘-terfuran (5), and from the α,α‘-linked triheterocycles containing thiophene and furan, bis(5-methyl-2-furyl)thiophene (6) and bis(5-methyl-2-thienyl)furan (7), were generated in fluid solution with trifluoroacetic acid (TFA) or mixtures of TFA and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP), in the presence or absence of thallium(III) trifluoroacetate as oxidant, and analyzed by electron paramagnetic resonance. The hyperfine coupling (hc) constants were assigned by comparison with those from 5,5‘-dimethyl- (3) and 5,5‘-di- tert -butyl-2,2‘,5‘,2‘‘-terthiophene (4) and by investigation into the deuterated species generated in solution with deuteriotrifluoroacetic acid and, in the case of 5 •+, 6 •+, and 7 •+ confirmed by theoretical calculations. The parent compounds 1, 5, 6, and 7 were synthesized by known procedures. Cyclic voltammetry of them in dimethylformamide using tetrabutylammonium hexafluorophosphate or perchlorate as electrolyte display irreversible oxidation peaks. The anodic peak for the oxidation of terfuran 5 is lower than that of bifuran 1, and anodic peaks for the oxidation of the trimers with furan rings 6 and 7 are lower than those for terthiophenes 3 and 4 .