Synthesis and reactivity of the macrobicyclic complexes (1,5,8,12-tetraaza-17-oxabicyclo[10.5.2]-nonadecane)cobalt(III) perchlorate ([Co(L₁)(CIO₄)]-(CIO₄)₂), [(chloro(1,4,8,11-tetraaza-17-oxabicyclo-[9.5.3]nonadecane)cobalt(III) perchlorate ([Co(L₂)-(CI)](CIO₄)₂)

The potentially penta-coordinating ligands L₂ and L₃ 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 (L₃)-. A similar procedure is outlined for the dimethylated macrobicycle (L₄), 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 L₁ 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 L₂ exhibit remarkable kinetic stability. Studies on the anation of the [Co(L₁)(H₂O)](CIO₄) ₃ with chloride ions in acidic media are consistent with the reaction of both the proton-related complex and the [Co(L₁)(H ₂O)]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.