Electrochemical behaviour of amino substituted β-amino α,β-unsaturated ketones: A computational chemistry and experimental study

The synthesis, identification and electrochemical properties are reported here, for a series of five novel and seven known amino substituted beta-amino alpha,beta-unsaturated ketones (bidentate N,O-ligands) of the type CH3COCHC(NHR)CH3, where R= H, Ph, CH2Ph, CH(CH3)(2), p-CF3-Ph or p-Bu-t-Ph (Series 1), as well as type PhCOCHC(NHR)CH3, where R = H, Ph, p-NO2-Ph, 3,5-di-Cl-Ph, 2-CF3-4-Cl-Ph, and also PhCOCHC(NHPh)CF3 (Series 2). The cyclic voltammograms measured in CH3CN, generally exhibit both a chemically and electrochemically irreversible reduction peak between -1.2 V and -3.1 V vs FcH/FcH(+), producing an unstable radical anion, for most of these 1,3-amino ketones. Only ligands PhCOCHC(NHPh)CH3, PhCOCHC(NHPh)CF3 and PhCOCHC(NH(p-NO2-Ph))CH3, showed reversible electrochemical behaviour, at higher scan rates. Density functional theory (DFT) calculations proved the unpaired spin density in the radical anion to be distributed over the pseudo-aromatic O-C-C-C-N backbone of the 1,3-amino ketones, extending further over the phenyl rings of the phenyl-containing ligands. Various DFT calculated energies, such as the energy of the lowest unoccupied molecular orbital (the orbital into which the electron is added upon reduction), as well as the DFT calculated gas phase adiabatic electron affinities, relate linearly to the experimentally measured reduction potential. These obtained linear relationships confirmed that good communication via conjugation exists, between the R substituent on the amino group and the rest of the 1,3-amino ketone. (C) 2018 Elsevier Ltd. All rights reserved.