The Synthesis, Electrochemistry and Reactivity of Binuclear Copper(I) Complexes as Mimics of Protein Active Sites

A series of binuclear copper(I) complexes has been synthesized and characterized as potential models for binuclear copper protein sites. The first group of compounds was prepared by the condensation of 2-hydraxy-5-methylisophthalaldehyde with a variety of primary amines (RNH2) followed by the addition of Cu(CH3CN)4BF4 and pyrazolate (pz), 3, 5-dimethyl pyrazolate (Me2pz) and 7-azaindolate (aza) anions (X) to yield [Equation. See abstract in scanned thesis for details]. A crystal and molecular structural analysis of [Equation. See abstract in scanned thesis for details] (R = 2-(2'-pyridyl)ethyl) showed each copper bound to the phenoxide oxygen, as well as to one imine and one pyrazolate nitrogen. The pyridine nitrogens were not coordinated to copper, but an intermolecular Cu-Cu interaction (2.97 Å) was observed. Overall coordination about copper(I) is best described as highly distorted pyramidal, with long axial (Cu-Cu) coordination. The copper-copper interaction appears to be associated with a ca. 600 nm (solid state) absorption which is not present in solution or in the solid state for compounds with bulky "side arms" (R). All compounds are proposed to be three-coordinate in solution, but they have exhibited no tendency to bind additional ligands such as CO or pyridine. Most of the binuclear copper(I) complexes gave quasi-reversible electrochemical behavior, with two distinct one-electron processes. The reduction potentials were varied over a wide range by modifications of the sidearms (R) and the bridge (X), with the most positive potentials observed for R = t-butyl and X = 3, 5-dimethylpyrazolate (Ef1 = +O.239, Ef2 = + O.80 V vs. nhe). Biological implications of the observed reactivities and redox properties of these compounds are discussed.