We report the synthesis of octacationic macrocycles based on the porphyrazine (tetraazaporphyrin) core. The first stage is the synthesis of Mg(II) 2,3,7,8,12,13,17,18-octakis(4-pyridyl)porphyrazine, [Mgpz(pyr)8], and the parent [H2pz(pyr)8]. Both compounds are freely soluble in aqueous acid due to protonation of the pyridyl groups but with concomitant loss of Mg2+ by the latter. Methylation of [H2pz(pyr)8] gives the octacation, 2,3,7,8,12,13,17,18-octakis(N-methyl-4-pyridiniumyl)porphyrazine, [H2pz(Me-pyr)8]8+, which is freely soluble in water as the chloride salt. The peripheral charges greatly lower the pKa values of the pyrrole protons of [H2pz(Me-pyr)8]8+ in aqueous solution. Global fitting of optical pH titration curves gives pKa values for the first and second deprotonations of 6.3 and 8.8 in 2.0 M NaCl and 4.1 and 5.6 at 0.1 M NaCl. The analysis further gives the UV - visible spectra of the [H2pz(Me-pyr)8]8+, [Hpz(Me-pyr)8]7+, and [pz(Me-pyr)8]6+ species. The free-base compound [H2pz(Me-pyr)8]8+ rapidly incorporates a variety of metal ions (Ba(II), Cd(II), Co(II), Cu(II), Mn(III), Ni(II), Pd(II), and Zn(II)) to form [Mpz(Me-pyr)8]8+. We present the complete synthesis and characterization of the [Nipz(Me-pyr)8]8+ and [Cupz(Me-pyr)8]8+ derivatives.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry