24315-60-4Relevant academic research and scientific papers
Impact of distortion of porphyrins on axial coordination in (porphyrinato)zinc(II) complexes with aminopyridines as axial ligands
Kojima, Takahiko,Nakanishi, Tatsuaki,Honda, Tatsuhiko,Harada, Ryosuke,Shiro, Motoo,Fukuzumi, Shunichi
, p. 727 - 734 (2009)
A series of (porphyrinato)zinc(II) compounds were synthesized with use of 5,10,15,20-tetraphenylporphyrin (H2TPP), 2,3,5,10,12,13,15,20- octaphenylporphyrin (H2OPP), and 2,3,5,7,8,10,12,13,15,17,18,20- dodecaphenylporphyrin (H2DPP). Those compounds form complexes with aniline, pyridine, and 3- and 4-aminopyridines as axial ligands. X-ray crystallography was performed on the complexes with 3-aminopyridine (3-AP) and 4-aminopyridine (4-AP) as axial ligands. 3-Aminopyridine was revealed to bind through the amino group to the Zn(OPP), exhibiting intermolecular π-π interaction between 3-AP and one of the pyrrole rings and intermolecular NH-π interactions of the coordinated amino group with two β-phenyl groups of an adjacent molecule. In solu-tion, the aminopyridines form a single species at ambient temperature and are assumed to have pyridine coordination through the aromatic pyridine nitrogen atom. Variable-temperature NMR spectroscopy in CD2Cl 2 indicates that two different species exist at lower temperatures, suggesting that amino-bound complexes of 3-AP can be formed as a metastable species in solution, which is stabilized in the crystal as a result of noncovalent interactions. The binding constants of aminopyridines to the three kinds of (porphyrinato)zinc complexes reveal enhancement of the axial ligation by virtue of the distortion of the porphyrin ring. Wiley-VCH Verlag GmbH & Co. KGaA, 2009.
Reactions of metalloporphyrin π radicals. 1. Complexation of zinc tetraphenylporphyrin cation and anion radicals with nitrogenous bases
Kadish,Shiue,Rhodes,Bottomley
, p. 1274 - 1277 (2008/10/08)
Stability constants for TPPZn with 20 nitrogenous bases were obtained by the method of proportional absorbances. These results were combined with electrochemical data to obtain stability constants for the reaction of TPPZn radical cations and radical anions with ligands. Values of log β1 ranged from 1.64 to 4.59 for ligand addition to [TPPZn]+ and from 1.47 to 3.50 for addition to [TPPZn]-. Only five-coordinate complexes were observed. These measurements represented the first values of stability constants obtained for nitrogeneous base addition to porphyrin π radicals. The changes in stability constants observed as a function of ligand pKa allowed the tuning of the zinc radical cation half-wave potential between 0.83 and 0.74 (vs. SCE) and the radical anion potential between -1.38 and -1.49 V. The ligand additions proceeded in a chemically reversible fashion over the experimental time frame. Thin-layer spectra for oxidations showed slight spectral differences between [TPPZn]+ and [TPPZn(L)]+ but were almost totally insensitive to a specific L. The possibility of an alternate oxidative pathway to the β-substituted pyrrole product was examined and found not to be operative for this time frame and solvent system.
