Metal Complexes with Macrocyclic Ligands. Part XXXVIII. Steric effects in the copper(II) and nickel(II) complexes with tetra-N-alkylated 1,4,8,11-tetraazacyclotetradecanes

✍ Scribed by Martin R. Oberholzer; Markus Neuburger; Margareta Zehnder; Thomas A. Kaden

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: German
• Weight: 518 KB
• Volume: 78
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19950780220

✦ Synopsis

Abstract

A series of tetra‐N‐alkylated 1,4,8,11‐tetraazacyclotetradecanes have been synthesized and their complexation potential towards Ni^2+^ and Cu^2+^ studied. In the case of sterically demanding alkyl substituents, such as i‐Pr, PhCH~2~, or 2‐MeC~6~H~4~CH~2~, no metal complexes are formed, whereas for substituents such as Me, Et, and Pr, the metal ion is incorporated into the macrocycle. The spectroscopic properties of the Ni^2+^ and Cu^2+^ complexes in aqueous solution indicate that, depending on the sterical hindrance of the N‐substituents, the complexes are either square planar or pentacoordinated. All these Ni^2+^ and Cu^2+^ complexes react with N to give ternary species, the stability of which have been determined by spectrophotometric titrations. The tendency to bind N decreases with increasing steric hindrance of the alkyl substituents. The X‐ray studies of the Ni^2+^ complex with the macrocycle 11, substituted by two Me and two Pr groups, and that of the Cu^2+^ complex with the tetraethyl derivative 8 show that in the solid state, the metal ions exhibit square planar coordination with a small distortion towards tetrahedral geometry.