Metal ion complexes of 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetra-aza-cyclotetradeca-4,11-diene. Part I. Some nickel(II) and copper(II) compounds

Abstract

Preparations and properties of nickel(II) and copper(II) complexes of the tetra-aza macrocycle (1) formed by reaction of benzylideneacetone with diaminoethane are reported. Stereochemical evidence favouring assignment of the structure 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene for (1), present in the trans-trans-meso-configuration, is presented. Compounds with two configurations of the cation [Ni(1)]²⁺ arising from the chiral co-ordinated secondary amino-groups were isolated. The β(N-meso) configuration is optimum for planar bcde-co-ordination and singlet ground-state square-planar salts [Ni(β1)]X₂, X = ClO₄^–, BF₄^–, I^–, and 0·5ZnCl₄^2– and trans-octahedral triplet ground-state compounds trans-[Ni(β1)X₂], X = Cl^–, NCS^–, CH₃CO₂^–, or NO₃^– and trans-[Ni(β1)(NH₃)(H₂O)](ClO₄)₂ were prepared. The α(N-rac) configuration is optimum for folded abcd-co-ordination and triplet ground-state compounds with chelates occupying the ef co-ordination sites, [Ni(α1)en](ClO₄)₂, [Ni(α1)acac]ClO₄, and [{Ni(α1)}₂C₂O₄](ClO₄)₂ were prepared. Treatment of these compounds with acid removed the chelate by protonation while preserving the α configuration to give square planar salts [Ni(α1)](ClO₄)₂ and [Ni(α1)]ZnCl₄, metastable with respect to their β configurational isomers. The co-ordination stereochemistry of (1) is discussed and ¹H n.m.r., i.r., and d-d electronic spectra are reported. It is concluded that the metastability of the α configuration of (1) in planar co-ordination arises from strain introduced by the presence of a phenyl group as an axial substituent on one six-membered chelate ring. The compounds [Cu(β1)]X₂, X = ClO₄^–, NO₃^–, or NCS^– and [Cu(β1)]Cl₂,4H₂O are assigned tetragonal structures. The i.r. spectra of the perchlorate and nitrate indicate weak metal-anion interactions.