BIBRACHIAL LIGANDS FROM STERICALLY PROTECTED TETRA-AZAMACROCYCLES - SYNTHESIS OF BIS(N-2-CYANOETHYL)TET-A AND THE CRYSTAL-STRUCTURE OF ITS COPPER(II) COMPLEX

The preparation of the ligand 12,14-hexamethyl-1,4,8,11-tetra-azacyclo tetradecan (L) is described. The ligand can be reduced with H-2/Raney nickel in the presence of NaBH4 to give the bis(N-3-aminopropyl) deriv ative. The red copper(II) complex [CuL](ClO4). 0.5 MeOH has been chara cterised by X-ray crystallography. The complex has v(C=N) at 2225 cm(- 1) identical to that found in the free ligand, indicating that there i s no interaction between the central metal ion and the pendant cyanoet hyl groups. The crystal structure confirms that the copper(II) is four -coordinate and planar with the four ring nitrogens acting as donors. The Cu-N bond lengths are 2.068(6) and 1.980(5) Angstrom. The macrocyc lic ligand has the centrosymmetric trans-III configuration with chair six-membered chelate rings and gauche five-membered rings. The methyl groups on C(3) and C(5) are equatorial.