Porphyrazinehexamines and Dinitroporphyrazines: Synthesis, Characterization, and Complementary Electrochemistry.
Unsymmetrical porphyrazines, M[pz(H)(2)(R)(6)], with three substituted pyrroles (substituents, R = -NMe(2), propyl, or 4-tert-butylphenyl) at the periphery and one unsubstituted pyrrole have been synthesized from inexpensive and readily available materials. Linstead crossover macrocyclization of 8 with 9, 11, and 12 gave pigments 1, 3, and 5, respectively. Subsequent demetalation by treatment with TFA gave free-base porphyrazines 2, 4, and 6. Generally, pyrrolines 11 and 12 are better co-cyclization partners and give higher yields for the desired unsymmetrical porphyrazines compared to maleonitriles 9 and 10 when co-cyclized with 8. Nickel porphyrazine 7 was obtained by reaction of 6 with Ni(OAc)(2) in chlorobenzene and dimethylformamide. Both free-base and nickel porphyrazines (6 and 7) were readily nitrated by nitrogen dioxide in CH(2)Cl(2), yielding dinitroporphyrazines 18 and 19, respectively. Electrochemical studies have shown that porphyrazinehexamine 2 is easy to oxidize, having the first oxidation at E(1/2) = - 0.18 V, which is 0.91 and 1.04 V lower than that of 4 and 6, respectively. Dinitroporphyrazine 18, however, displays a 0.6 V of cathodic shift for the two reversible reduction waves compared to those observed for the parent porphyrazine 6.
Nie
Hanlin
H
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Department of Chemistry, Imperial College of Science, Technology and Medicine, London SW7 2AY, U.K.
Barrett
Anthony G. M.
AG
Hoffman
Brian M.
BM