Super-Charged Porphyrazines: Synthesis and Physical Properties of Octacationic Tetraazaporphyrins.
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 [H(2)pz(pyr)(8)]. Both compounds are freely soluble in aqueous acid due to protonation of the pyridyl groups but with concomitant loss of Mg(2+) by the latter. Methylation of [H(2)pz(pyr)(8)] gives the octacation, 2,3,7,8,12,13,17,18-octakis(N-methyl-4-pyridiniumyl)porphyrazine, [H(2)pz(Me-pyr)(8)](8+), which is freely soluble in water as the chloride salt. The peripheral charges greatly lower the pK(a) values of the pyrrole protons of [H(2)pz(Me-pyr)(8)](8+) in aqueous solution. Global fitting of optical pH titration curves gives pK(a) 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 [H(2)pz(Me-pyr)(8)](8+), [Hpz(Me-pyr)(8)](7+), and [pz(Me-pyr)(8)](6+) species. The free-base compound [H(2)pz(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.
Anderson
Máirín E.
ME
Departments of Chemistry, Northwestern University, Evanston, Illinois 60208, and Imperial College of Science, Technology and Medicine, London, England.
Barrett
Anthony G. M.
AG
Hoffman
Brian M.
BM