Oxygenation of Cobalt Porphyrinates: Coordination or Oxidation?

Li, Jianfeng; Noll, Bruce C.; Oliver, Allen G.; Ferraudi, G.; Lappin, A. Graham; Scheidt, W. Robert

doi:10.1021/ic902309f

Cited by 46 publications

(42 citation statements)

References 52 publications

(64 reference statements)

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“…The synthesis of [Co(TpivPP)(1-EtIm)(O 2 )] is similar to that of [Fe(TpivPP)(1-MeIm)(O 2 )], but the precursor is five-coordinate [Co(TpivPP)(1-EtIm)] 12 instead of six-coordinate [Fe(TpivPP)(1-MeIm) 2 ]. Crystals of [Co(TpivPP)(1-EtIm)(O 2 )] containing the six-coordinate porphyrinate and benzene solvate, have been characterized at various temperatures and cooling regimes.…”

Section: Resultsmentioning

confidence: 99%

“…We have previously reported the synthesis and structural characterization of five-coordinate [Co(TpivPP)-(2-MeHIm)], 12 the precursor to the six-coordinate oxygen derivative. However, the reaction of [Co(TpivPP)(2-MeHIm)] with O 2 in benzene in the presence of a small amount of ethanol unexpectedly gave two different crystalline forms of a cobalt(III) product and not the desired dioxygen adduct.…”

Section: Discussionmentioning

confidence: 99%

“…12 Moderate-size single crystals of [Co(TpivPP)(2-MeHIm)] were exposed at room temperature to pure dioxygen gas saturated with ethanol vapor. Crystals were obtained from exposure to a) a ~1 atm dioxygen atmosphere for 3 days or b) to a ~5 atm dioxygen atmosphere for 5 days in a high pressure reaction cylinder (Parr Instrument; Model 4635).…”

Section: Methodsmentioning

confidence: 99%

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Structural Insights into Ligand Dynamics: Correlated Oxygen and Picket Motion in Oxycobalt Picket Fence Porphyrins

Noll

Oliver

et al. 2012

J. Am. Chem. Soc.

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Two different oxygen-ligated cobalt porphyrins have been synthesized and the solid-state structures have been determined at several temperatures. The solid-state structures provide insight into the dynamics of Co–O2 rotation and correlation with protecting group disorder. [Co(TpivPP)(1-EtIm)(O2)] (TpivPP = picket fence porphyrin) is prepared by oxygenation of [Co(TpivPP)(1-EtIm)2] in benzene solution. The structure at room temperature has the oxygen ligand within the ligand binding pocket and disordered over four sites and the trans imidazole is disordered over two sites. The structure at 100 K, after the crystal has been carefully annealed to yield a reversible phase change, is almost completely ordered. The phase change is reversed upon warming the crystal to 200 K, whereupon the oxygen ligand is again disordered but with quite unequal populations. Further warming to 300 K leads to greater disorder of the oxygen ligands with nearly equal O2 occupancies at all four positions. The disorder of the t-butyl groups of the protecting pickets is correlated with rotation of the O2 around the Co–O(O2) bond. [Co(TpivPP)(2-MeHIm)(O2)] is synthesized by a solid-state oxygenation reaction from the five-coordinate precursor [Co(TpivPP)(2-MeHIm)]. Exposure to 1 atm of O2 leads to incomplete oxygenation, however, exposure at 5 atm yields complete oxygenation. Complete oxygenation leads to picket disorder whereas partial (40%) oxygenation does not. Crystallinity is retained on complete degassing of oxygen in the solid, and complete ordering of the pickets is restored. The results should provide basic information needed to better model M–O2 dynamics in protein environments.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Structural Insights into Ligand Dynamics: Correlated Oxygen and Picket Motion in Oxycobalt Picket Fence Porphyrins

Noll

Oliver

et al. 2012

J. Am. Chem. Soc.

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“…56 Both have the imidazole on the side opposite the protected ligand binding pocket. The axial imidazole ligand is disordered in accord with the required twofold symmetry of the observed space group.…”

Section: Discussionmentioning

confidence: 99%

“…The disorder in the coordinated imidazole in both the five- and the six-coordinate complexes is possibly dynamic as well, the ordering observed in one cobalt derivative shows that crystal packing can allow for the movement (rotation) of the imidazole. 56 …”

Section: Discussionmentioning

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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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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Conversion of Cobalt(II) Porphyrin into a Helical Cobalt(III) Complex of Acyclic Pentapyrrole

Yamanishi¹,

Miyazawa²,

Yairi³

et al. 2011

Angewandte Chemie

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Conversion of artificial porphyrin to acyclic polypyrrole by oxidation is important not only for model reactions of heme oxygenase (HO), which converts heme to biliverdin, [1][2][3] but also for the syntheses of new acyclic polypyrroles. [4][5][6][7][8][9][10] Biliverdin-type ligands are nonplanar tetrapyrrole derivatives and have been utilized for the syntheses of metal complexes with helical structures that are easily racemized, owing to its low steric hindrance for interconversion. [11][12][13][14][15][16] In contrast, metal complexes bearing acyclic polypyrroles constructed of more than five pyrroles are still rare because of the limited availability of synthetic routes to prepare them. [17][18][19][20][21][22] As an exceptional example, a new dicopper(II) complex bearing acyclic heptapyrrolic helices has been prepared from dicopper(II) heptaphyrin by reaction with O 2 . [7] In this reaction, O 2 was not activated at the metal center but reacted with the heptaphyrin ligand directly.Two intrinsic effects of the coordination environment around heme on the activation of the O 2 molecule have been proposed in the biological system. One is the electron donation from coordinating bases such as imidazole and thiolate at the fifth coordination site to the iron center, and the other is the hydrogen bond from the histidine residue to the O 2 molecule bound at the metal center. When these two effects contribute cooperatively, this activation mechanism is called a "push-pull" mechanism. [3,23] To mimic the pull effects, some porphyrin ligands bearing carboxylic acid, which could form a hydrogen bond to the bound O 2 , have been designed and synthesized. [4,[23][24][25] For example, Chang and co-workers have shown that Co II porphyrin complex bearing naphthoic acid, [Co(npca-por)], converted to metal-free biliverdin-type acyclic polypyrrole by reaction with O 2 . This reaction proceeds under ambient condition without coordination of any bases at the axial site. [4] The authors proposed that in this system, the carboxylic acid group protonated the coordinating O 2 molecule to yield a Co III À OOH species as an intermediate. Although this system mimicked the pull effect well, porphyrin complexes which require both push and pull effects for the cleavage of the porphyrin ring are still not known.Recently, we designed a new porphyrin ligand (amtpp; Scheme 1) that has an amide group in the ortho position of a phenyl ring of tetraphenylporphyrin (H 2 tpp) to mimic the pull effect by histidine residue in the biological system. We found that the imidazole adduct [Co(amtpp)(1-MeIm)] (1-MeIm = 1-methylimidazole) activated O 2 , thus converting to a new Co III helical complex with a coiled acyclic pentapyrrole-type ligand, despite the fact that the Co II complex [Co(amtpp)] (1) was inert to air (Scheme 1). Moreover, we have found that chiral axial ligands (S)-nicotine and (S)-cotinine induced the (M)-helical form preferentially in this conversion system. Herein, we report the synthesis and structure of the Co-amtpp complex and the un...

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Oxygenation of Cobalt Porphyrinates: Coordination or Oxidation?

Cited by 46 publications

References 52 publications

Structural Insights into Ligand Dynamics: Correlated Oxygen and Picket Motion in Oxycobalt Picket Fence Porphyrins

Structural Insights into Ligand Dynamics: Correlated Oxygen and Picket Motion in Oxycobalt Picket Fence Porphyrins

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

Conversion of Cobalt(II) Porphyrin into a Helical Cobalt(III) Complex of Acyclic Pentapyrrole

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