Synthesis and Characterization of New trans N,N′-Disubstituted Macrocyclic “tet a” Ligands and Their Copper(II) and Nickel(II) Complexes: Structural, Electrochemical, Magnetic, and Catalytic Studies

• Published in: Bulletin of the Chemical Society of Japan 2004-06, Vol.77 (6), p.1153-1159
• Main Authors: Sengottuvelan, Nallathambi, Saravanakumar, Duraisamy, Narayanan, Vengidusamy, Kandaswamy, Muthusamy, Chinnakali, Kandaswamy, Senthilkumar, Gopal
• Format: Article
• Language: English
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.77.1153

New trans-disubstituted macrocyclic ligands (L1), trans-1,8-[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}]-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane, and (L2), 1,8-[N,N′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}]-4,11-dimethyl-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane, were synthesized. The ligands were characterized by elemental analysis, IR, 1H and 13C NMR spectral analyses. The ligand L1 crystallized as monoclinic in the space group P21/n, and the final R-value was found to be 0.062. Copper(II) and nickel(II) complexes of these ligands were prepared and characterized by elemental analysis, IR, UV–visible, FAB-mass spectral studies. Electrochemical studies of the nickel(II) complexes show one-electron quasireversible reduction around −1.00 to −1.13 V and one-electron quasireversible oxidation around 1.00 to 1.14 V. The copper(II) complexes show one-electron quasireversible reduction around −0.93 to −1.10 V. ESR spectral studies of the copper(II) complexes show hyperfine splitting with a g|| value of 2.31, a g⊥ value of around 2.02 and an A value of 160 G. The magnetic moment values (μeff) of the Cu(II) complexes fall in the range of 1.71 to 1.72 B.M. at room temperature (298 K). The rate-constant values of the catalytic hydrolysis of p-nitrophenyl phosphate for the copper(II) complexes were in the range 6.3 × 10−3 to 12.2 × 10−3 min−1 and for the nickel(II) complexes in the range 10 × 10−3 to 14 × 10−3 min−1. The rate-constant values of the catalytic oxidation of catechol to o-quinone were in the range 9.4 × 10−3 to 13.4 × 10−3 min−1 for the copper(II) complexes. The copper(II) and nickel(II) complexes of ligand L2 have higher catalytic activity than that of ligand L1.