Europium Triple-Decker Complexes Containing Phthalocyanine and Nitrophenyl–Corrole Macrocycles

A series
of europium triple-decker complexes containing phthalocyanine
and nitrophenyl–corrole macrocycles were synthesized and characterized
by spectroscopic and electrochemical methods in nonaqueous media.
The examined compounds are represented as Eu2[Pc­(OC4H9)8]2­[Cor­(Ph)n(NO2Ph)3–n], where n varies from 0 to 3, Pc­(OC4H9)8 represents the phthalocyanine macrocycle,
and Cor indicates the corrole macrocycle having phenyl (Ph) or nitrophenyl
(NO2Ph) meso substituents. Three different methods were
used for syntheses of the target complexes, two of which are reported
here for the first time. Each examined compound undergoes five reversible
one-electron oxidations and 3–5 one-electron reductions depending
upon the number of NO2Ph substituents. The nitrophenyl
groups on the meso positions of the corrole are highly electron-withdrawing,
and this leads to a substantial positive shift in potential for the
five oxidations and first reduction in CH2Cl2, PhCN, or pyridine as compared to the parent triple-decker compound
with a triphenylcorrole macrocycle. The measured E1/2 values are linearly related to the number of NO2Ph groups on the corrole, and the relative magnitude of the
shift in potential for each redox reaction was used in conjunction
with the results from thin-layer spectro-electrochemistry to assign
the initial site of oxidation or reduction on the molecule. The nitrophenyl
substituents are also redox-active, and each is reduced to [C6H4NO2]− in a separate
one-electron transfer step at potentials between −1.12 and
−1.42 V versus saturated calomel electrode.