Synthesis of Lateral Macrobicyclic Compartmental Ligands: Structural, Magnetic, Electrochemical, and Catalytic Studies of Mono- and Binuclear Copper(II) Complexes

A series of putative mono- and binuclear copper(ll) complexes, of general formulas [CuL](C104) and [Cu2L](C104)2, respectively, have been synthesized from lateral macrocyclic ligands that have different compartments, originated from their corresponding precursor compounds (PC-1,3,4:9,10-dibenzo-1,12-[/V,Ar-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclotetradecane; and PC-2,3,4:9,10-dibenzo-1,12-[/V,-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclopentadecane). The precursor compound PC-1 crystallized in the triclinic system with space group PI. The mononuclear copper(ll) complex [CuL](C104) is crystallized in the monoclinic system with space group P2i/c. The binuclear copper(ll) complex [Cu2L](CIO4)2 is crystallized in the triclinic system with space group PI; the two Cu ions have two different geometries. Electrochemical studies evidenced that one quasireversible reduction wave (Epc = -0.78 to -0.87 V) for mononuclear complexes and two quasi-reversible oneelectron-transfer reduction waves (E1pc = -0.83 to -0.92 V, E2pc = -1.07 to -1.38 V) for binuclear complexes are obtained in the cathodic region. Room-temperature magnetic-moment studies convey the presence of antiferromagnetic coupling in binuclear complexes [mu ett = (1.45-1.55)mu b], which is also suggested from the broad ESR spectra with g = 2.10-2.11, whereas mononuclear complexes show hyperfine splitting in ESR spectra and they have magneticmoment values that are similar to the spin-only value [mu ett=(1.69-1.72)mu b]. Variable-temperature magnetic susceptibility study of the complex shows that the observed -2J value for the binuclear complex [Cu2L](C104)2 is 214 cm. The observed initial rate-constant values of catechol oxidation, using complexes as catalysts, range from 4.89 x 10 to 5.32 x 10 min and the values are found to be higher for binuclear complexes than for the corresponding mononuclear complexes.