N-Methylation of macrocyclic hexaaminecobalt(III) complexes

Abstract

Reaction between formaldehyde and the pendant arm macrocyclic complex (trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)cobalt(III) [CoL¹]³⁺ yielded the diimine derivative trans-6,13-dimethyl-6,13-bis(methyleneamino)-1,4,8,11-tetraazacyclotetradecane (L³) as its cobalt(III) complex. Reduction of the imines has been achieved with NaBH₄ and the meso and rac cobalt(III) complexes of trans-6,13-dimethyl-6,13-bis(methylamino)-1,4,8,11-tetraazacyclotetradecane (L⁵) have been prepared. Crystal structures of the macrocyclic complexes [CoL¹][ClO₄]₃, [CoL³][ClO₄]₃ and meso-[CoL⁵][ClO₄]₃·2H₂O were determined and some unusual structural, spectroscopic and electrochemical variations observed going from the parent hexaamine [CoL¹]³⁺ to [CoL³]³⁺ (diimine) and ultimately to [CoL⁵]³⁺ (bis-N-methylated hexaamine).