New Macrocyclic Complexes Derived From Cobalt(III) Cage Complexes

Abstract

The synthesis and partial characterization of several green complexes, derived from the products of the reactions between [Co(Cl₂-sar)]³⁺ (Cl₂-sar = 1,8-dichloro-3,6,10,13,16,19- hexaazabicyclo [6.6.6] icosane ) and zinc powder in water, are described. Most of the complexes appear to have [CoCl₂(N₄)] chromophores , where N₄ denotes the tetraaza macrocyclic ligand , 6,13-dimethylene-1,4,8,11-tetraazacyclotetradecane (L1). For trans-[CoCl₂(L1)]⁺, three isomers due to different configurations about the asymmetric nitrogen donor centres were obtained and characterized by the electronic absorption and ¹³C n.m.r. spectra. Their stereochemistry is discussed and compared with that of 1,4,8,11-tetraazacyclotetradecane on the basis of strain energy minimized calculations. A trans-[CoCl₂(H₂L2)]³⁺ complex containing a related macrocycle with a pendant ethane-1,2-diamine arm [H₂L²⁺, 6-(4-ammonio-2-azoniabutyl)-13-methylene-1,4,8,11-tetraazacyclotetradecane] was also isolated and characterized by X-ray crystallographic analysis. All these molecules are derived from the decomposition of zinc alkyl complexes formed by oxidative addition of zinc to the parent [Co^II(Cl₂-sar)]²⁺ ion in aqueous solution.