Synthesis and group electronegativity implications on the electrochemical and spectroscopic properties of diferrocenyl meso-substituted porphyrins

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 H-1 NMR clearly distinguished between them. Use of the CH2Cl2/0.1M [N(Bu-n)(4)][B(C6F5)(4)] solvent/supporting electrolyte system allowed good resolution between the two ferrocenyl CV waves with Delta E degrees' = 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. Delta E degrees' values for the Zn (10) and Ni (11) derivatives of 7 were 103 and 95 mV, respectively. The formal reduction potentials, E degrees', 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, chi(Zn2+) or chi(Ni2+), of the coordinated central cations. Differences in E degrees' of 6-11 with respect to that of meso tetraphenyl porphyrin, 2Htpp, were found to be related to the group electronegativities, chi(C6H5), chi(C6F5), chi(Fc), and chi(Fc+), of each meso substituent.