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 1 H NMR clearly distinguished between them. Use of the CH 2 Cl 2 /0.1M [N( n Bu) 4 ][B(C 6 F 5 ) 4 ] solvent/supporting electrolyte system allowed good resolution between the two ferrocenyl CV waves with Δ E °‘ = 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 . Δ E °‘ 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, χ Zn2+ or χ Ni2+, 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, χ C6H5, χ C6F5, χ Fc, and χ Fc+, of each meso substituent.