Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different?

Li, Jianfeng; Nair, Smitha M.; Noll, Bruce C.; Schulz, Charles E.; Scheidt, W. Robert

doi:10.1021/ic702498c

Cited by 42 publications

(60 citation statements)

References 66 publications

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“…16, 30 [Fe(TpivPP)(1-EtIm) 2 ] (30 mg) was dried in vacuum for 30 mins. Drops of 1-ethylimidazole and benzene (~5 mL) were then transferred into the Schlenk by cannula.…”

Section: Methodsmentioning

confidence: 99%

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Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: Structural and Mössbauer Investigations

Noll

Oliver

et al. 2013

J. Am. Chem. Soc.

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Disorder in the position of the dioxygen ligand is a well-known problem in dioxygen complexes and in particular in those of picket fence porphyrin species. The dynamics of Fe–O2 rotation and tert-butyl motion in three different picket fence porphyrin derivatives has been studied by a combination of multi-temperature X-ray structural studies and Mössbauer spectroscopy. The structural studies show that the motions of the dioxygen ligand also require motions of the protecting pickets of the ligand binding pocket. The two motions appear to be correlated and the temperature-dependent change in the O2 occupancies can not be governed by a simple Boltzmann distribution. The three [Fe(TpivPP)(RIm)(O2)] derivatives studied have RIm = 1-methyl-, 1-ethyl-, or 2-methylimidazole. In all three species there is a preferred orientation of the Fe–O2 moiety with respect to the trans imidazole ligand and the population of this orientation increases with decreasing temperature. In the 1-MeIm and 1-EtIm species, the Fe–O2 unit is approximately perpendicular to the imidazole plane whereas in the 2-MeHIm species the Fe–O2 unit is approximately parallel. This reflects the low energy required for rotation of the Fe–O2 unit and the small energy differences in populating the possible pocket quadrants. All dioxygen complexes have a crystallographically required twofold axis of symmetry that limits the accuracy of the determined Fe–O2 geometry. However, the 80 K structure of the 2-MeHIm derivative allowed for the resolution of the two bonded oxygen atom positions and provided the best geometric description for the Fe–O2 unit. The values determined are: Fe–O = 1.811(5) Å, Fe–O–O = 118.2(9)°, O–O = 1.281(12) Å, and an off-axis tilt of 6.2°. The demonstration of the off-axis tilt is a first. We present detailed temperature-dependent simulations of the Mössbauer spectra that model the changing value of the quadrupole splitting and line widths. Residuals to fits are poorer at higher temperature. We believe that this is consistent with the idea that population of the two conformers are related to the concomitant motions of both Fe–O2 rotations and motions of the protecting tert-butyl pickets.

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“…16, 30 [Fe(TpivPP)(1-EtIm) 2 ] (30 mg) was dried in vacuum for 30 mins. Drops of 1-ethylimidazole and benzene (~5 mL) were then transferred into the Schlenk by cannula.…”

Section: Methodsmentioning

confidence: 99%

“…Reduced [Fe(II)(TpivPP)] 16 d , 30 was reacted with ~5 equiv of 2-methylimidazole in a mixed solution of benzene and ethanol. The mixture was stirred for 30 min and transferred into 8 mm × 250 mm glass tubes which were layered with heptane as nonsolvent.…”

Section: Methodsmentioning

confidence: 99%

Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: Structural and Mössbauer Investigations

Noll

Oliver

et al. 2013

J. Am. Chem. Soc.

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“…[21, 23] [ 57 Fe(TpivPP)(1-RIm) 2 ] (30 mg) was dried in vacuum for 30 mins. Drops of the imidazole and benzene (~5 mL) were then transferred into the Schlenk by cannula.…”

Section: Methodsmentioning

confidence: 99%

New Perspectives on Iron–Ligand Vibrations of Oxyheme Complexes

Peng

Barabanschikov

et al. 2011

Chemistry A European J

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We report our studies of the vibrational dynamics of iron for three imidazole-ligated oxyheme derivatives that mimic the active sites of histidine-ligated heme proteins complexed with dioxygen. The experimental vibrational data are obtained from nuclear resonance vibrational spectroscopy (NRVS) measurements conducted on both powder samples and oriented single-crystals, and which includes several in-plane (ip) and out-of-plane (oop) measurements. Vibrational spectral assignments have been made through a combination of the oriented sample spectra and predictions based on density functional theory (DFT) calculations. The twoFe–O2 modes that have been previously observed by resonance Raman spectroscopy in heme proteins are clearly shown to be very strongly mixed and are not simply either a bending or stretching mode. In addition, a third Fe–O2 mode, not previously reported, has been identified. The long-sought Fe–Im stretch, not observed in resonance Raman spectra, has been identified and compared with the frequencies observed for the analogous CO and NO species. The studies also suggest that the in-plane iron motion is anisotropic and is controlled by the orientation of the Fe–O2 group and not sensitive to the in the in-plane Fe–Np bonds and/or imidazole orientations.

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“…This mode of bonding is thermodynamically favoured in order to retain the aromaticity within the imidazole ring [62]. The coordination about the iron is the familiar 3-legged piano-stool geometry [65] and falls within the range (1.958(5)-1.999(2) Å) reported for iron imidazole complexes [36,66,67]. The Fe-N bond (1.977 Å) in 7 is marginally shorter than the average Fe-N bond (1.978 Å) in 8 ( Table 3).…”

Section: CMmentioning

confidence: 84%

Reactions of N-heterocyclic ligands with substitutionally labile organometallic complexes, [(η5-C5R5)Fe(CO)2E]BF4

M’thiruaine

Friedrich

Changamu

et al. 2012

Inorganica Chimica Acta

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Relative Axial Ligand Orientation in Bis(imidazole)iron(II) Porphyrinates: Are “Picket Fence” Derivatives Different?

Cited by 42 publications

References 66 publications

Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: Structural and Mössbauer Investigations

Correlated Ligand Dynamics in Oxyiron Picket Fence Porphyrins: Structural and Mössbauer Investigations

New Perspectives on Iron–Ligand Vibrations of Oxyheme Complexes

Reactions of N-heterocyclic ligands with substitutionally labile organometallic complexes, [(η5-C5R5)Fe(CO)2E]BF4

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