Synthesis, structural studies and photochemistry of cobalt(iii) complexes of anthracenylcyclam macrocycles

Abstract

This work reports the syntheses, structures and some photochemistry in DMF of the cobalt complexes trans-[Co^III(2)Cl₂]Cl·0.5CH₃OH and trans-[Co^III(3)Cl₂]Cl·4H₂O, where 2 is 6-(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,7-dione and 3 is 6-(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane. In the preparation of the macrocyclic ligand, 3, the formation of a polycyclic bis(aminal) intermediate and its subsequent acid hydrolysis to 3 is a cleaner route than the traditional procedure in which the analogous dioxocyclam 2 is reduced with borane reagents. The crystal structure of trans-[Co^III(3)Cl₂]Cl·4H₂O shows that the macrocycle adopts the trans-III conformation, in which the anthracene moiety is extended away from the cobalt ion and the anthracene to Co separation is 7.22 Å. For the related complex trans-[Co^III(2)Cl₂]Cl·0.5CH₃OH, however, the anthracene is bent over the highly conjugated tetracycle and significant interactions between the anthracene and the complex occur. A novel new complex, trans-[Co(12)Cl₂] (where 12 is 5,7-hydroxy-6-oxo-1,4,8,11-tetraazacyclotetradecane-4,7-diene) which is a degradation product of the complex trans-[Co^III(2)Cl₂]Cl is also reported.