REMOTE SUBSTITUENT EFFECTS IN PYRROLE-2-CARBOXALDIMINATE COMPLEXES OF COPPER(II)

A number of copper(II) bis chelates with anions of pyrrole-2-carboxaldehyde Schiff bases have been synthesized. The amine substituents are phenyl moieties, which themselves bear in the para position a series of substituents, ranging from the electron-withdrawing nitro group to the relatively electron-releasing dimethylamino group. Investigation of the CuII-CuI redox potentials shows that electron-withdrawing groups increase the stability of copper(I) relative to copper(II). There are correlations among E1/2, the basicity of the precursor anilines, and the Taft parameter, σ°, of the ring substituent, the plot of nFE1/2/23RTvs. 2σx° having a slope of+1.28. ESR spectroscopy shows the complexes to have essentially square-planar geometry. The response of the redox potential and the insensitivity of the ESR parameters to the ring substituents are discussed in relationship to structural properties of protein-bound copper. © 1978, American Chemical Society. All rights reserved.