Chemistry of structurally developed macrocycles. Part 1. Complexation properties of NN′N″N‴-tetra(2-cyanoethyl)-1,4,8,11-tetra-azacyclotetradecane with nickel(II)

Abstract

Reaction of 1,4,8,11-tetra-azacyclotetradecane (cyclam) with excess of acrylonitrile yields quantitatively the tetracyanoethylated product. In the presence of donor anions this potentially eight-co-ordiante ligand behaves as a quadridentate ligand towards nickel(II) binding through the tertiary amine donors alone. The resulting complexes are generally five-co-ordinate (six-co-ordinate with NCS^–) having the ligand in a partially folded configuration. With perchlorate as anion a polymeric nickel(II) complex is formed which consists of five-co-ordinate metal centres linked together by intermolecularly bridging nitriles. Attempts to hydrolyse the nitrile groups of the free ligand to produce the tetra-amide or tetracarboxylic acid were unsuccessful. However, hydrolysis of the tetranitrile when co-ordinated to nickel(II) proceeds at neutral pH producing an octahedral complex containing the co-ordinated tetra-amide.