The potentially penta-coordinating ligands L-2 and L-3 have been synthesized by reaction of the 10-membered macrocycle 1,5-diaza-8-oxacyclodecane with either 1,9-dichloro-3,7-diazanonane-2,8-dione, and subsequent reduction of the diamide (3), or with 1,9-dichloro-3,7-(dimethyl)diazanonane-2,8-dione and reduction (L-3). A similar procedure is outlined for the dimethylated macrobicycle (L-4), based on the corresponding nine-membered 1,4-diaza-7-oxacyclononane. The Co(III) complexes of these ligands and of 1,5,8,12-tetraaza-17-oxabicyclo[10.5.2]nonadecane (L-1) have been prepared. Spectrophotometric determinations on the L-1 complex ion confirm the presence of two hydrogen ion related equilibria, one of which (pK = 2.2 +/- 0.2) is associated with the proposed replacement of the apical ether oxygen by a water molecule that is bound to the metal centre and hydrogen bonded to the ether. The species derived from L-1 and L-2 exhibit remarkable kinetic stability. Studies on the anation of the [Co(L-1)(H2O)](ClO4)(3) with chloride ions in acidic media are consistent with the reaction of both the proton-related complex and the [Co(L-1)(H2O)](3+) ion. Whilst complex ions containing two secondary NH groups maintain the metal-ion coordination in strongly acidic media, corresponding species with ligands containing all four tertiary amine sites are subject to attack by protons leading to a relatively facile demetallation of the complexes. The latter finding is supported by kinetic studies and mass spectrometric fragmentation patterns of the ions.
Canadian Journal of Chemistry-Revue Canadienne De Chimie Vol. 83, no. 6, p. 894-902