The hydrolysis of coordinated amidines in the sexadentate complex u-fac-2,3-Bis[(2-aminoethyl)(methyl)aminoethylimino]-1- methylpiperazinecobalt(III) perchlorate

Abstract

The title complex u-fac-[Co(amam)]³⁺ (1) has a sexadentate ligand which involves a novel diamidine arrangement of an N,N'-disubstituted amidine and a trisubstituted amidine, each amidine group being coordinated through one nitrogen. It is inert in acid but it hydrolyses in base in two clean sequential stages through an amidine imide complex (2) to the diimide complex u-fac-[1,14-diamino-3,12-dimethyl-3,6,9,12- tetraazatetradeca-6,8-diene-7,8-diolato(2-)]cobalt(III) ion (3). The structures of complexes (2) and (3) isolated as perchlorates have been characterized by ¹³C and ¹H n.mr.r spectra, electronic and infrared spectra, and by their unusual ion-exchange chromatographic behaviour. Complexes (2) and (3) exist as the deprotonated forms of the amides, and become partially protonated only at [H⁺] ≥ 1 M. The structures of (2) and (3) demonstrate that coordinated amidines base-hydrolyse specifically to retain the Co-N-C bond, and that the less highly substituted amidine group hydrolyses the more readily.