PROBING THE CATALYTIC PROPERTIES OF COPPER(II) COMPLEXES OF APPENDED CYCLAMS - CORRELATIONS BETWEEN CATALYSIS AND STABILITY-CONSTANTS OR ELECTROCHEMICAL PROPERTIES

Copper(II) complexes were prepared from the dinucleating octadentate l igand tetra-1,4,8,11-(2 pyridylmethyl)-1,4,8,11-tetraazacyclotetradeca ne (tpmc). The five-coordinate complexes [Cu-2(tpmc)X](ClO4)(3) (with X = F, Cl, Br, or I) were characterized by chemical analysis, absorpti on spectroscopy and cyclic voltammetry. The data show the dinculear Cu (II) complexes to be five-coordinate with a bridging halide donor. All display chemically reversible redox behavior, with two one-electron r eductions observed in acetonitrile at glassy carbon. The values for E- 0' range from 118 to - 126 mV vs SCE for the first reduction, and from -122 to -241 mV for the second reduction. Catalysis of the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone using these c omplexes was studied. Correlations among reactivity,binding constants, and reduction potentials were determined. These correlations show tha t the rate of the oxidation reaction is linearly correlated to the bin ding of the halide bridge; the most reactive complex ([Cu-2(tpmc)I] (C lO4)(3)) is the one with the smallest binding constant while the least reactive ([Cu-2(tpmc)Cl] (ClO4)(3)) has the largest binding constant. Electrochemical data showed a non-linear relationship between the com plexes' ability to oxidize 3,5-di-tert-butylcatechol and their reducti on potentials. Comparisons to the naturally occurring enzyme tyrosinas e are made. (C) 1998 Elsevier Science Ltd. All rights reserved.