NEW MACROCYCLIC COMPLEXES DERIVED FROM COBALT(III) CAGE COMPLEXES

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 maocrocyclic ligand, 6,13-dimethylene-1,4,8,11-tetraazacyclotetradecane(Ll). For trans-[CoCl2(Ll)]+, three isomers due to different configurations about the asymmetric nitrogen donor centres were obtained and characterized by the electronic absorption and C-13 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-[CoC12(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.