ELECTRON-TRANSFER AND ION-PAIRING .18. RADICAL-ANIONS AND RADICAL ION-PAIRS OF AZA-SUBSTITUTED NAPHTHOQUINONES AND ANTHRAQUINONES

The redox behaviour of aza-substituted naphtho- and anthraquinones, which offer O = C - C = N - chelate tongs for an advantageous five-membered ring metal cation complexation, is investigated by a combination of cyclovoltammetric and ESR/ENDOR spectroscopic measurements. The formation of paramagnetic contact ion pairs like [(quinoline-5,8-semiquinone). (-)Me(+)]., with Me(+) = Li(+), Na(+), Tl(+), or of triple ion radical cations like [(1.4-diazo-9, 10-anthrasemiquinone)-Me2+].+, with Me+ = Li+, Na+ is corroborated both by shifts of the second reduction potential of up to 0,67 V for e.g. quinoline 5,8-quinone upon addition of Li+[B(C6H5)4]- to its DMF solution and by the observation of ESR/ENDOR metal couplings.