Reverse pulse polarography for EC processes. Electrochemistry of 1,1′-trimethylene-bis-(4-carbomethoxypyridinium) ion

Abstract

The 1,1′-trimethylene-bis-(4-carbomethoxypyridinium) ion ( 3 ++ ) is reduced in tetrabutylammonium perchlorate (TBAP)+CH 3 CN at the dropping mercury electrode to the biradical 3 in an EC-type reaction, consisting of a reversible charge transfer 3 ++ +2e − = 3 op , followed by intramolecular cyclization ( 3 op being the open form of the biradical) to cyclomers. Depending on the time scale, different cyclomers are formed: in the sub-millisecond time range, the coupled chemical reaction results in the reversible formation of fast forming species 3 ff , cyclomers with π-type interactions ( cis -cyclomer B). In the time range of seconds, the slow forming species 3 sf with σ-type interactions ( trans -cyclomer) are dominant. The forward and backward rate constants of the reaction 3 ff = 3 sf are determined by the reverse pulse polarographic method: k f =3.0 s −1 , k b =1.0 s −1 . In the presence of metallic ions, 1:1 biradical–metal complexes are formed reversibly. The stoichiometry and formation constants are determined by the reverse pulse polarographic method: K 3 Li/op =1.2×10 4 l mol −1 ; K 3 Mg/op =1.1×10 5 l mol −1 .