Chemical Equilibrium between Metalloporphyrins (MTPP and M(o-Cl)TPP) and Basic Ligands(L). (M = Zn2+, Cu2+, Ni2+: TPP = tetraphenylporphyrin, (o-Cl)TPP = tetrakis (ortho-chlorophenyl)porphyrin: L = imidazole, pyridine, 1-methylimidazole, 2,6-lutidine)

摘要

The axial ligations of nitrogenous bases (pyridine, imidazole, 1-methylimidazole and 2,6-lutidine) to Zn(￥±)-, Cu(￥±)-, and Ni(￥±)-tetrakis(o-chlorophenyl)porphyrin(o-ClTPP), and -tetraphenylporphyrin (TPP) were investigated in organic solvents (CH2Cl2, C6H6, CH3NO2, (CH3)2CO, CHCl3, DMF and DMSO) and at 0.01M of ionic strength. The equilibrium constants for the ligation reactions of methalloporphyrins were determined using spectrophotometric method at 15?-35?é. In case of M(￥±)-TPP the equilibrium constants K were considerably larger than those of M(￥±)-(o-Cl)TPP, depending on steric effect of the porphyrin. The linear relationships between logK of the axial ligation and pKa of nitrogenous base were shown in M(￥±)-TPP, but not in M(￥±)-(o-Cl)TPP. The stabilities of MTPP(L) were controlled by the reation enthalpy and entropy, while those of M(o-Cl)TPP almost by the reaction entropy. The coordinating power of solvent to the methalloporphyrin were also studied in CHCl3, (CH3)2CO, DMF and DMSO. From those results the solvent effects on the equilibrium constants were discussed.