Synthesis and Characterization of Pendant Arm Encapsulated Complexes of Cobalt(III)

The synthesis and characterization of an octahedral cobalt(III) complex of the octaamine ligand 5,5-bis(4-amino-2-azabutyl)-3,7-diazanonane-1,9-diamine, [co( asen )]3+, is described. Two approaches to the preparation of encapsulated derivatives of [Co(asen)]3+ are also described. The first approach involves reaction of [Co(asen)]3+ with nitromethane and formaldehyde in the presence of base. After extensive chromatographic purification [(1-(4-amine-2-azabutyl)-8-nitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane )cobalt(III)]5+ was isolated. The second more convenient method employs precautionary protection of the pendant primary amine of [Co( asen )]3+, as the benzenesulfonate, prior to reaction with the same capping reagents. Both approaches result in an encapsulated complex bearing a pendant 4-amine-2-azabutyl moiety. The protecting group is stable under reaction conditions required for successive chemical modifications of the capping nitro group to amine, chloro and proton capped cages, but is readily removed in refluxing acidic solution.