Synthesis and Group Electronegativity Implications on the Electrochemical and Spectroscopic Properties of Diferrocenyl meso-Substituted Porphyrins

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Abstract

Two different condensations of appropriate dipyrromethanes and aldehydes resulted in two structural isomers of metal-free, meso-substituted diferrocenyldipentafluorophenyl porphyrins, one with the ferrocenyl groups in the 5,15 positions, 6, and the other with the ferrocenyl groups in the 5,10 positions, 7. UV/vis spectroscopic and cyclic voltammetric (CV) techniques could not unambiguously distinguish between the isomers, but 1H NMR clearly distinguished between them. Use of the CH2Cl2/0.1M [N(nBu)4][B(C6F5)4] solvent/supporting electrolyte system allowed good resolution between the two ferrocenyl CV waves with ΔE°‘ = 111 and 115 mV for 6 and 7, 102 mV for the Zn derivative of 6, namely 8, and 109 mV for 6's Ni derivative, 9. ΔE°‘ values for the Zn (10) and Ni (11) derivatives of 7 were 103 and 95 mV, respectively. The formal reduction potentials, E°‘, at which the two observed ring-based electrochemical reductions and one oxidation process were detected, varied in a manner that depended on the cationic electronegativities, χZn2+ or χNi2+, of the coordinated central cations. Differences in E°‘ of 6−11 with respect to that of meso tetraphenyl porphyrin, 2Htpp, were found to be related to the group electronegativities, χC6H5, χC6F5, χFc, and χFc+, of each meso substituent.

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