METAL-COMPLEXES WITH MACROCYCLIC LIGANDS .43. TETRAAZAMACROCYCLIC NICKEL(II) AND COPPER(II) COMPLEXES WITH ALIPHATIC METHYLTHIO-SUBSTITUTEDAND METHOXY-SUBSTITUTED PENDANT CHAINS

The 14-membered tetraazamacrocyclic Ni2+ and Cu2+ complexes of 4 hylth io)ethyl]-1,4,8,11-tetraazacyclotetradecane), 5 hylthio)ethyl]-1,4,8,1 1-tetraazacyclotetradecane), and 7 hylthio)ethyl]-1,4,8,11-tetraazacyc lotetradecane), with one, two, and four methylthio-substituted pendant chains, respectively, and the Ni2+ complex of 6 (1,4-dimethyl-8,11-bi s -methoxyethyl)-1,4,8,11-tetraazacyclotetradecane), with two methoxy- substituted pendant chains, were synthesized and their chemistry studi ed with regard to modelling F430. Solution spectra in H2O, MeCN, and D MF indicate participation of the side chain in metal coordination when the donor group is a thioether, whereas no coordination with the meta l ion is observed with the ether group. Similarly the X-ray structures of the thioether-containing compounds [Ni(5)](ClO4)(2), [Cu(5)](ClO4) (2), and [Cu(7)](ClO4)(2) show a coordination number of 5, whereas tha t of [Ni(6)](ClO4)(2) with ether pendant chains, shows a coordination number of 4. Cyclic voltammetry of these complexes in MeCN reveals tha t Ni2+ is reversibly reduced to Ni+ between - 0.64 and - 0.77 V vs. SC E, the potential being influenced by the nature and number of the pend ant chains. At more negative potentials, the thioether is cleaved, whe reby a thiol is formed; the thiol is then oxidized at ca. + 0.8 V vs. SCE, when a glassy carbon electrode is used, or at ca. 0 V vs. SCE at a dropping Hg electrode. No cleavage of the ether bond in [Ni(6)](ClO4 )(2) is observed under similar conditions.