OXYGENATION OF A COPPER(I) COMPLEX OF A BINUCLEATING MACROCYCLIC SCHIFF-BASE LIGAND DERIVED FROM 1,4,7-TRIAZAHEPTANE AND FURAN-2,5-DICARBOXALDEHYDE

The ligand 3,6,9,16,19,22-hexaazatricyclo[22.2.1.1(12,14)]octacosa-1(26),2,9,11,13,15,22,24-octaene ((FD)2(DIEN)2) was prepared from 1,4,7-triazaheptane and furan-2,5-dicarboxaldehyde. A dinuclear copper(I) complex is formed by reacting (FD)2(DIEN)2 with 2 equiv of Cu(CH3CN)4(ClO4) in medium formed by a 1:3 mixture of acetonitrile and methanol. The oxygenation reaction of the dinuclear Cu(I) complex was followed spectrophotometrically and by oxygen absorption at pH 9.0 and 5-degrees-C. The crystal structure of the green degradation product formed from the dioxygen complex was determined by X-ray analysis. The results reveal that the copper centers are bridged by hydroxo and methoxo groups. Crystals are monoclinic, space group C2/c, with a = 22.248 (8) angstrom, b = 10.194 (4) angstrom, c = 13.986 (10) angstrom, beta = 110.48 (4)degrees, and Z = 4. The Cu...Cu distance is 2.958 (3) angstrom. An unusual coordination mode, which is distorted square planar, is found around each copper atom. The formation of a binuclear Cu(I) dioxygen complex within the macrocycle and the lack of a oxygen insertion reaction are explained on the basis of the bridging oxygen-containing furan groups in place of an aromatic o-xylyl group.