SOLUTION NMR STUDIES AND CRYSTAL STRUCTURE OF THE WATER-SOLUBLE IRON(III) PORPHYRIN IRON 5,10,15,20-TETRAKIS(2,3,5,6-TETRAFLUORO-4-N,N,N-TRIMETHYLANILINIUMYL)PORPH YRIN ([FETF(4)TMAP](5+))

摘要

The crystal structure of [Fe-III(TF(4)TMAP)(H2O)(2)](CF3SO3)(5) . 2CH(3)CN . 2H(2)O (a = 13.065(2) Angstrom, b = 13.375(2) Angstrom, c = 13.839(2) Angstrom, alpha = 110.97 degrees, beta = 104.97 degrees, gamma = 94.22 degrees, V = 2144.2(6) Angstrom(3), Z = 1) shows that the Fe(III) has two axial coordinated waters. This is in accord with solution NMR results which show that small concentrations of water (>5%) in an acetonitrile solution displace the CF3SO3- ligand from the iron(III) porphyrin. The F-19 NMR spectra of an acetonitrile solution of the hydroxo form of this Fe(III) porphyrin show changes as the water content increases above 70% which are interpreted as indicating a change from five-coordinate [Fe-III(TF(4)TMAP)OH](4+) to six-coordinate [Fe-III(TF(4)TMAP)(H2O)OH](4+). Variable-temperature F-19 NMR has been used to analyze the slow interconversion of [Fe-III(TF(4)TMAP)(H2O)(2)](5+) and [Fe-III(TF(4)TMAP)OH](4+). The kinetic results suggest that interconversion occurs mainly via bimolecular reaction between the aqua and hydroxo forms with k = 1.6 x 10(6) M-1 s(-1) (298 K) and E-a = 6.7 +/- 0.4 kcal mol(-1). This rate constant is significantly smaller than the reported interconversion rate constants for other aqua/hydroxo complexes. [References: 50]