Unsymmetrical porphyrazines, M[pz(H)2(R)6], with three substituted pyrroles (substituents, R = -NMe2, 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 CH2Cl2, 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.
ASJC Scopus subject areas
- Organic Chemistry