Cobalt(II) and Cobalt(III) Complexes of Pentaaza Macrocyclic Ligands. Isomeric Composition and Hydrolysis Reactions of the Complexes of Eight Ligands With 15-Membered to 20-Membered Macrocyclic Rings

Abstract

Synthesis and characterization of cobalt(III) complexes of the pentaaza macrocyclic ligands 1,4,7,10, 13-pentaazacyclopentadecane, ( cpad ), 1,4,7,10,13-pentaazacyclohexadecane, ( ched ), 1,4,7,10,14-pentaazacycloheptadecane, ( chad ), 1,4,7,11,14-pentaazacycloheptadecane, ( chbd ), 1,4,7,11, 15-pentaazacyclooctadecane, ( coad ), 1,4,8,11,15-pentaazacyclooctadecane, ( cobd ) are described. Of the different isomeric forms possible for each complex only one geometric isomer and one or two of the possible diastereoisomers have been isolated. The products of the induced acid hydrolysis reactions of the bromo and chloro complexes with these ligands have been identified by means of ¹³C n.m.r. spectroscopy. Nitrato complexes are commonly produced when the reaction proceeds in nitrate media. The reactions of the [Co( cpad )X]ⁿ⁺ and [Co( chbd )X]ⁿ⁺ complexes proceed with the apparent inversion of a coordinated nitrogen in strongly acid media. Cobalt(II) complexes of the ligands 1,4,8,12,16-pentaazacyclononadecane ( cnad ) and 1,5,9,13,17-pentaazacycloeicosane (ceic) were prepared. These complexes could not be oxidized to cobalt(III) complexes and the available evidence suggests that they are five-coordinate square-pyramidal complexes in the solid state and in solution.