Macrocycle Formation Through Carbon Acid–Formaldehyde Condensation Reactions of Bis(propane-1,2-diamine)- and Bis(2-methylpropane-1,2-diamine)-copper(II) Ions

Abstract

The reaction of the bis(1,2-diamine)copper(II) complexes of racemic propane-1,2-diamine (pn) and 2-methylpropane-1,2-diamine (dmen) with formaldehyde and nitroethane in methanol under basic conditions yields minor macrocyclic condensation products in addition to the major acyclic products. Where C-pendant methyl groups on the pair of coordinated diamines are in cis dispositions, the first –NH–CH₂–C(CH₃)(NO₂)–CH₂–NH– ring formation occurs at amine pairs distant from these C-methyl substituents, and further reaction to yield a macrocycle is not observed. However, where the C-methyl substituents are in transdispositions, the chemistry proceeds to yield the macrocycle. Commencing with pn, trans-(6,13-diammonio-2,6,9,13-tetramethyl-1,4,7,10-tetraazacyclotetradecane)copper(II) perchlorate formed and crystallized in the space group P 2₁/n, with a9· 782(2), b 9·2794(6), c 17·017(4) Å, β 103·24(1)°. The copper ion is found in a square-planar environment, with the two methyl groups of the pn residues and the pairs of introduced pendant groups all in trans arrangements.