SYNTHESIS AND CHARACTERIZATION OF AN OCTACATIONIC IRON(III) TETRAPHENYLPORPHYRIN, WHICH IS SOLUBLE IN WATER AND NON-MU-OXO DIMER FORMING

摘要

Synthesis and characterization {electrospray mass spectroscopy, UV/vis spectra, and H-1 and C-13 NMR, and purity by gel electrophoresis} of the sterically hindered, polycationic water-soluble iron(III) meso-5,10,15,20-tetrakis(2,4,6-trimethyl-3 ,5-bis{ alpha-N,N,N-trimethylammoniummethyl}phenyl)porphyrin octachloride dihydrate (3)- Fe-III(X)(2) (where X = H2O and/or HO-, dependent on pH) is reported. The synthesis of the ligand 3H(2) rests on the discovery of a highly selective bromomethylation reaction of meso-5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrin (tetramesitylporphyrin, TMPH(2)) with formaldehyde and HBr/acetic acid. The electrophoretic mobilities of octacationic 3H(2) and (3)Fe-III(H2O)(2) were comparable, being slightly more than twice the mobilities of the free bases and iron(III) complexes of the commercially available tetracationic porphyrins tetrakis(N-methylpyridyl)porphyrin (TMPyPH(2)) and tetrakis(4-trimethylammoniumphenyl)porphyrin (TMAPH(2)). mu-Oxo dimer formation is not detectable with (3)Fe-III(zX)(2). The determined pK(a)s of the water ligands of polycationic (3)Fe-III(H2O)(2) increase with increasing ionic strength, whereas the pK(a) values of the previously studied polyanionic tetrakis(2,6-dimethyl-3-sulfonatophenyl) porphyrin iron(III) {(1)Fe-III(H2O)(2)} decrease with increasing ionic strength. This is consistent with an increase in the electropositive nature of the iron center of(3)Fe-III(H2O)(2). A marked tendency of cationic (3)Fe-III(X)(2) to Ligate buffer anions was observed. This feature is not shared by the polyanionic (1)Fe-III(H2O)(2). Spectrophotometric titrations of (3)Fem(H2O)(2) with acetate buffer and fitting of absorbance changes at 398 nm vs [HOAc](t) afforded a pH-independent binding constant K-B of 42 M(-1) for monoligation of acetate. [References: 33]