Dynamics and thermodynamics of axial ligation in metalloporphyrins. 4. Kinetics of porphyrin inversion in high-spin ferric complexes

Snyder, Richard V.; Mar, Gerd N. La

doi:10.1021/ja00431a014

Cited by 22 publications

(9 citation statements)

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“…All pairs do average since the activated [(TrPP)Fe III I 2 ] - subunit has the plane of symmetry through the porphyrin skeleton. The analogous mechanism was presented previously for the (TPP)Fe III X systems . This process also results in a mutual interconversion of the iron(III) diporphyrin enantiomers.…”

Section: Resultssupporting

confidence: 69%

¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

et al. 1999

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The 1H NMR spectra of iron(III) complexes of dimeric 5,5‘-bis(10,15,20-triphenylporphyrin) [(TrPPH2)2], 5,5‘-bis(10,15,20-tris(p-methoxyphenyl)porphyrin) [(Tr(p-MeOP)PH2)2], and hybrid (TrPPH2)(Tr(p-MeOP)PH2) and the respective monomeric 5,10,15-triphenylporphyrin (TrPPH2) and 5,10,15-tris(p-methoxyphenyl)porphyrin [Tr(p-MeOP)PH2] have been investigated in order to elucidate an impact of a direct meso − meso linkage on the electronic structure of corresponding high- and low-spin iron(III) porphyrins. The following species, covering the representative spin/oxidation states, have been investigated: (TrPP)2(FeIIICl)2 (high spin); [(TrPP)2(FeIII(CN)2)2]2- (low spin); [(TrPP)2(FeIIICl)2]+ (high-spin iron(III), diporphyrin radical); [(TrPP•)2(FeIIICl)2]2+ (high-spin iron(III), diradical of diporphyrin). The iron(III) diporphyrins (TrPP)2(FeIIICl)2, [(TrPP)2(FeIII(CN)2)2]2-, {[(TrPP)FeIII(CN)2][(Tr(p-MeOP)P)FeIII(CN)2]}2-, and [(TrPP)2(FeIIICl)2]2+ revealed the 1H NMR features which have been typically encountered in the spectra of the relevant monomeric complexes. Thus magnetic interactions between two subunits via skeleton appear to be minor. The characteristic broadening and/or paramagnetic shifts of 3-H and 7-H resonances were determined and are diagnostic features of the meso − meso linkage. One-electron, ligand-based oxidation of (TrPP)2(FeIIICl)2 to produce [(TrPP)2(FeIIICl)2]+ was observed with the unpaired electron delocalized over both macrocycles. The structure of (Tr(p-MeOP)P)ZnII·0.4CH2Cl2, the fundamental building block in synthesis of diporphyrins, was determined by X-ray crystallography. (Tr(p-MeOP)P)ZnII crystallizes in the monoclinic space group C2/c with a = 47.744(9) Å, b = 9.090(2) Å, c = 15.571(2) Å, β = 93.770(13)°, and Z = 8. The refinement of 494 parameters and 4361 reflections yields R 1 = 0.0756, wR 2 = 0.2169. The (Tr(p-MeOP)P)ZnII presents characteristic features of zinc(II) tetraphenylporphyrin. The molecular periphery of (Tr(p-MeOP)P)ZnII has a fully exposed meso position and two partially exposed pyrrole rings.

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Section: Resultssupporting

confidence: 69%

¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

et al. 1999

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“…Figure shows possible dynamic processes to be considered in these complexes. They are (i) inversion of the deformed porphyrin ring as shown in process (a), (ii) site exchange of a ferric ion across the porphyrin ring via dissociation and association of chloride as shown in process (b), and (iii) rotation of phenyl groups about C meso −C phenyl bonds(not shown in Figure ). , If excess chloride exists in solution, the site exchange of a ferric ion would take place by an associative mechanism given in process (c) . At a low temperature where all of the three processes are frozen, each of the methyl, ortho, and meta protons of [Fe(OMTPP)Cl]SbCl 6 should give two signals.…”

Section: Discussionmentioning

confidence: 99%

“…We ascribed it to the phenyl rotation by the reason described later in this paper. It should be noted that the sample must be very pure since addition of 0.05 equiv of tetrabutylammonium chloride caused considerable effect on the line shape of each signal as shown in Figure S10 of the Supporting Information; two signals observed for the methyl, ortho, and meta protons at 25 °C changed to a single line due to the enhanced rate for site exchange of the ferric ion by the associative process …”

Section: Discussionmentioning

confidence: 99%

Barriers to Inversion of Nonplanar Ferric Porphyrin Radical Cations: Comparison with the Corresponding Neutral Complexes

1999

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Barriers to inversion of the highly deformed porphyrin rings in two ferric porphyrin radical cations, [Fe(OMTPP)Cl]SbCl6 and [Fe(OETPP)Cl]SbCl6 where OMTPP and OETPP are dianions of 2,3,7,8,12,13,17,18-octamethyl- and 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin, respectively, have been determined by the dynamic NMR method. Inversion barrier of [Fe(OMTPP)Cl]SbCl6 is estimated to be 14.8 kcal mol-1 (72 °C) which is higher than that of the corresponding neutral porphyrin complex [Fe(OMTPP)Cl] by more than 4 kcal mol-1. Increase in barrier to inversion has also been observed in [Fe(OETPP)Cl]SbCl6, though the precise determination is hampered in this case due to the occurrence of site exchange of the ferric ion across the porphyrin ring; the latter process is verified because the activation free energies obtained from the line shape analysis of the meta and methyl signals are quite close, 18.1 (113 °C) and 17.9 (113 °C) kcal mol-1, respectively. Thus, the inversion barrier in [Fe(OETPP)Cl]SbCl6 is supposed to be ≫18 kcal mol-1. Since the inversion barrier in the corresponding neutral porphyrin complex [Fe(OETPP)Cl] is reported to be 15.8 kcal mol-1, the barrier has increased by ≫2 kcal mol-1. These results are interpreted in terms of the enhanced nonplanarity of the radical cations as compared with the corresponding neutral complexes. The interaction between porphyrin a2u and iron d x 2 - y 2 orbitals in the radical cations, which is expected to be strengthened in the deformed structure, could be one of the reasons for the conformational change.

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“…T'2a for pyrrole-H (in PFeL2+X-) is given by the usual slow exchange limit form,17•26 i.e., -'2 1 -T2a 1 + Ta 1 (10) where is the observed pyrrole-H line width and T2a~ĉ haraterizes the line width in the absence of exchange. Since 72a = T(a, and ra-1 increases with temperature, we expect the 7,ia/7,2a ratio to deviate appreciably from unity as we enter the region where the pyrrole-H is broadened.…”

Section: Discussionmentioning

confidence: 99%

Dynamics and thermodynamics of axial ligation in metalloporphyrins. 6. Axial lability of nitrogenous bases in low-spin ferric complexes and the role of five-coordinate transient species

Jd¹,

Gn²,

Tj³

1977

J. Am. Chem. Soc.

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Dynamics and thermodynamics of axial ligation in metalloporphyrins. 4. Kinetics of porphyrin inversion in high-spin ferric complexes

Cited by 22 publications

References 10 publications

¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

Barriers to Inversion of Nonplanar Ferric Porphyrin Radical Cations: Comparison with the Corresponding Neutral Complexes

Dynamics and thermodynamics of axial ligation in metalloporphyrins. 6. Axial lability of nitrogenous bases in low-spin ferric complexes and the role of five-coordinate transient species

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Dynamics and thermodynamics of axial ligation in metalloporphyrins. 4. Kinetics of porphyrin inversion in high-spin ferric complexes

Cited by 22 publications

References 10 publications

1H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

1H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

Barriers to Inversion of Nonplanar Ferric Porphyrin Radical Cations: Comparison with the Corresponding Neutral Complexes

Dynamics and thermodynamics of axial ligation in metalloporphyrins. 6. Axial lability of nitrogenous bases in low-spin ferric complexes and the role of five-coordinate transient species

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¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)

¹H NMR Investigations of Triphenylporphyrin Metal Complexes and Electronic Interactions in Iron(III) Complexes of meso−meso-Linked 5,5‘-Bis(10,15,20-triphenylporphyrin)