Reduction of copper tetracyanotetraphenylporphyrin in nonaqueous media - formation of copper(I)

Abstract

The total electrochemical reduction of copper tetracyanotetraphenylporphyrin, (CN)/sub 4/(TPP)Cu, was investigated in dimethylformamide (DMF) by the techniques of polarography cyclic voltammetry, thin-layer spectroelectrochemistry, ESR spectroscopy, and extended Huckel calculations. The ESR results establish the existence of a Cu(II) dianion. The electrochemical reactions of (TPP)Cu and (CN)/sub 4/(TPP)Cu are compared, and the differences in redox behavior can be rationalized by the calculations. Unlike (TPP)Cu, which may be reduced by a total of six electrons in four steps, (CN)/sub 4/(TPP)Cu is reduced by seven electrons in five steps. This new wave occurs at E/sub 1///sub 2/ = -1.95 V in DMF and is attributed to reduction of the Cu(II) dianion to yield a Cu(I) complex. Formation of this species is reversible on the cyclic voltammetry time scale and an electronic spectrum has been obtained. This spectrum consists of a split Soret band at 390.0 and 480.4 nm and a strong band in the visible at 688.2 nm.