The Influence of Alkyl Substituents on Carbon Acid Formaldehyde Condensation Reactions of Bis(alkane-1,2-diamine)copper(II) Ions

Abstract

The reaction of the bis (1,2-diamine)copper(II) complexes of ethane-1,2-diamine (en), propane-1,2-diamine ( pn ) and 2-methylpropane-1,2-diamine ( dmen ) with formaldehyde and nitroethane in methanol under basic conditions yields macrocyclic and acyclic condensation products with two or one new -NH-CH₂-C(Me)(NO₂)-CH₂-NH- links introduced respectively between pairs of cis-disposed primary amines, and where the ratio of products is, surprisingly, significantly altered by C-methyl substitution on the parent ethane-1,2-diamine chelate . Under identical reaction conditions, the ratio of acyclic to macrocyclic product varied from 2:3 (en) to 10:1 ( pn ) to 50:1 ( dmen ) as first one methyl and then gem- dimethyl groups are attached to each parent chelate ring. That the reaction is influenced by substituent steric effects is supported by the structural characterization of the zinc-acid reduced and recomplexed acyclic species, which indicates that first ring formation occurs at amine pairs distant from the C-methyl substituents. The μ-chloro-bis (6-methyl-4,8-diazaundecane-2,6,10-triamine) dicopper (II) perchlorate crystallized in the space group C2/ c, a 23.003(6), b 12.641 (3), c 19.120(6) Ǻ, β 127.88(2)°, whereas the (2,6,10-trimethyl-4,8-diazaundecane-2,6,10-triamine)copper(II) perchlorate crystallized in the space group Cc2a, a 43.769(3), b 14.509(3), c 17.750(8) Ǻ. The copper ion is found in a distorted octahedral environment in the former with two complex units weakly bridged by a chloride anion, and in a square-based pyramidal environment in the latter.