Synthesis and reactivity of bis(ethane-1,2-diamine)(pyrrole-2-carboxylato)cobalt(III) ion
Chelated 4-hydroxypyrrolidine-2-carboxylic acid bound to the cobalt(III) ion reacts with thionyl chloride in dimethylformamide to give the chelated 4-hydroxy- and 4-chloro-2-pyrroline-2-carboxylato complexes via an established route for oxidising chelated amino acids to imino acids. Thionyl chloride also partly chlorinates the hydroxyamino acid to give the chloro derivative. Both the substituted pyrrolinecarboxylato complexes undergo rapid base catalysed eliminations to give the chelate [Co(en)2(L4)]Cl·2H2O (H2L4= pyrrole-2-carboxylic acid, en = ethane-1,2-diamine). The product is identical with that prepared from the pyrrole-2-carboxylate ion and [Co(en)2(OH)(OH2)]2+. The reactivity of the pyrrole carboxylate chelate towards electrophiles is very different from that of the free ligand.