Reactions of (10-Methyl-10-nitro-1,4,8,12-tetraaza-cyclopentadecane)copper(II) Ion in Aqueous Hydrochloric Acid, Including Zinc Reduction. Crystal-Structure of (2-methyl-1,4,8,11-tetraaza-cyclotetradec-1-ene)copper(II) Perchlorate

Abstract

The zinc/aqueous hydrochloric acid reduction of (10-methyl-10-nitro-1,4,8,12-tetraaza-cyclopentadecane)copper(II) ion, [Cu{(3)}]²⁺, yields the hydrochloride salts of the expected 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine (5) and also 14-amino-4,8,11-triazatetradecan-2-one (4) in approximately 2:1 ratio. Reaction of (10-methyl-10-nitro-1,4,8,12-tetraazacyclopentadecane)copper(II) ion in aqueous hydrochloric acid alone leads to bond scission and hydrolysis adjacent to the nitro-substituted carbon of the macrocycle to form 15- nitro-2,6,9,13-tetraazahexadecan-1-ol (7), which may be reduced in zinc/acid to the 15-amino-2,6,9,13-tetraazahexadecan-1-ol molecule (8). The acid hydrolysis reaction is not simply reversed by addition of base. The ring-opened species (7) is apparently an intermediate in formation of (4) from (3), via a metal- catalysed Nef reaction which converts the CH(NO₂)CH₃ arm into CO(CH₃). Reaction of (7) with Cu²⁺ at pH 9.5 slowly forms (2-methyl-1,4,8,11-tetraazacyclotetradec-1-ene )copper(II), [Cu{(6)}]²⁺, via formation of (4) and an intramolecular condensation around the metal ion. This complex was characterized by an X-ray crystal structure analysis of the perchlorate salt.