Generation of a stable .sigma.-bonded iron(IV) porphyrin. Formation and reactivity of [(OETPP)FeIV(C6H5)]n+ (n = 1-3; OETPP = dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin)

Kadish, Karl M.; Caemelbecke, Eric Van; D’Souza, Francis; Medforth, Craig J.; Smith, Kevin M.; Tabard, Alain; Guilard, Roger

doi:10.1021/om00031a005

Cited by 22 publications

(19 citation statements)

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“…This heme structural conservation is even observed in proteins for which there is a large natural variation in the amino acid sequence. ,7b This finding strongly suggests a biological function for the nonplanar structures. The possible functional importance of these nonplanar heme structures in proteins has been suggested by several other authors − and is supported by model studies in which nonplanar distortions have been shown to influence redox potential, ,9a, axial ligation, electron-transfer rates, 9a, and photophysical processes. − …”

Section: Introductionmentioning

confidence: 61%

Substituent-Induced Perturbation Symmetries and Distortions of meso-tert-Butylporphyrins

et al. 1998

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The out-of-plane and in-plane distortions of a series of nickel(II) meso-substituted porphyrins with 0, 1, 2, or 4 tert-butyl groups [nickel(II) porphine (NiP), nickel(II) mono-tert-butylporphyrin (NiMtBuP), nickel(II) di-tert-butylporphyrin (NiDtBuP), and nickel(II) tetra-tert-butylporphyrin (NiTtBuP)] are investigated using molecular mechanics (MM) calculations, X-ray crystallography, UV-visible absorption spectroscopy, and resonance Raman spectroscopy. MM calculations are used to predict the stable conformations for this series of porphyrins. The out-of-plane distortions are then analyzed in terms of displacements along the normal coordinates of the porphyrin macrocycle using a new normal-coordinate structural decomposition method. As expected, the distortions are found to occur primarily along the lowest-frequency normal coordinate of each symmetry type and the distortions could be adequately simulated using only the lowest-frequency normal coordinates as a basis (the minimal basis). However, the distortions could be simulated significantly more accurately by extending the minimal basis by including the second-lowest-frequency normal coordinate of all symmetries. Using the extended basis is most important for the in-plane distortions. Detailed analysis of the types of distortion revealed that both the out-of-plane and the in-plane distortions depend on the perturbation symmetry of the peripheral substituents. The symmetry primarily depends on the pattern of substitution (number and positions of substituents) and the orientations of substituents. Often the perturbation symmetry can be predicted for a given porphyrin simply from the possible orientations of the substituents. Then, the main type(s) of symmetric deformation occurring for each possible molecular symmetry can be readily predicted from a D(4)(h)() correlation table. The stable conformers predicted by MM for the series of tert-butyl-substituted porphyrins confirm this simple but informative approach. Experimental verification of the calculated contributions of the symmetric deformations is provided by normal-coordinate structural decomposition of the available X-ray crystal structures of NiP, NiMtBuP, and NiDtBuP. The solid-state results are also supported by the resonance Raman and UV-visible absorption spectroscopic characterization of the porphyrins in solutions. The X-ray crystal structure of NiMtBuP is reported here for the first time.

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Section: Introductionmentioning

confidence: 61%

Substituent-Induced Perturbation Symmetries and Distortions of meso-tert-Butylporphyrins

et al. 1998

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“…Nucleophilic addition of hydroxide ion to Au(III) 5,10,15,20-tetraphenylporphyrin also occurs at a meso -position with formation of the corresponding hydroxyphlorin, whereas the Cu(II), Pd(II), Cd(II) and Mn(III) complexes of TPP were unreactive under the same conditions [255]. Reactions of organometallic reagents with iron(III) porphyrins occur preferentially at the metal center with formation of σ-bonded species [256, 257]; migration of the σ-bonded groups (alkyl, vinyl, aryl) from the metal ion to the nitrogen atom is induced by oxidation or by acid treatment [258-264]. …”

Section: Porphyrin Functionalizationmentioning

confidence: 99%

Syntheses and Functionalizations of Porphyrin Macrocycles

Vicente¹,

Smith²

2014

COS

104

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Porphyrin macrocycles have been the subject of intense study in the last century because they are widely distributed in nature, usually as metal complexes of either iron or magnesium. As such, they serve as the prosthetic groups in a wide variety of primary metabolites, such as hemoglobins, myoglobins, cytochromes, catalases, peroxidases, chlorophylls, and bacteriochlorophylls; these compounds have multiple applications in materials science, biology and medicine. This article describes current methodology for preparation of simple, symmetrical model porphyrins, as well as more complex protocols for preparation of unsymmetrically substituted porphyrin macrocycles similar to those found in nature. The basic chemical reactivity of porphyrins and metalloporphyrin is also described, including electrophilic and nucleophilic reactions, oxidations, reductions, and metal-mediated cross-coupling reactions. Using the synthetic approaches and reactivity profiles presented, eventually almost any substituted porphyrin system can be prepared for applications in a variety of areas, including in catalysis, electron transport, model biological systems and therapeutics.

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“…Iron(IV) porphyrin π radical cations play an essential role in a number of oxidative catalytic processes including biological systems. − Although high-valent iron porphyrins are usually extremely reactive and thus difficult to characterize, the one- and two-electron oxidations of σ-bonded iron porphyrins such as (P)Fe(R), where P is a given porphyrin dianion, will lead first to an iron(IV) porphyrin and then to an iron(IV) porphyrin π radical cation, both of which have a stability that depends in large part upon the nature of the σ-bonded axial ligand (R) and the porphyrin macrocycle (P). , For example, the one-electron oxidation of (OETPP)Fe(C 6 H 5 ) which has a saddle-shaped nonplanar porphyrin macrocycle (OETPP = the dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin) leads to a relatively stable iron(IV) compound, [(OETPP)Fe IV (C 6 H 5 )] + . , In this regard, some octaalkyltetraphenylporphyrins, which are nonplanar as a result of steric crowding of the peripheral substituents, have been used as model compounds to investigate the consequences of nonplanar conformational distortions. − The further one-electron oxidation of [(OETPP) Fe IV (C 6 H 5 )] + leads to an Fe(IV) porphyrin π radical cation, formally an Fe(V) compound, and this is followed by migration of the σ-bonded C 6 H 5 ligand to a nitrogen of the porphyrin ring to give [( N -C 6 H 5 OETPP)Fe III ] 2+ . , A migration of the σ-bonded axial ligand from singly oxidized iron porphyrins with planar macrocycles such as (OEP)Fe(C 6 H 5 ) or (TPP)Fe(C 6 H 5 ) (OEP = the dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin and TPP = the dianion of 5,10,15,20-tetraphenylporphyrin) has long been known to occur, and the resulting migration product can be further oxidized at the metal center to give [( N -C 6 H 5 OEP)Fe III ] 2+ and [( N -C 6 H 5 TPP)Fe III ] 2+ in the presence of excess oxidizing agent or under the application of an applied oxidizing potential , but there has so far been no report in the literature on the kinetics of electron-transfer reactions for generation of iron(IV) porphyrins or iron(IV) porphyrin π radical cations prior to the migration step which occurs on a much longer time scale than the electron transfer. …”

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Electron-Transfer Kinetics for Generation of Organoiron(IV) Porphyrins and the Iron(IV) Porphyrin π Radical Cations

et al. 1999

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Homogeneous electron-transfer kinetics for the oxidation of seven different iron(III) porphyrins using three different oxidants were examined in deaerated acetonitrile, and the resulting data were evaluated in light of the Marcus theory of electron transfer to determine reorganization energies of the rate-determining oxidation of iron(III) to iron(IV). The investigated compounds are represented as (P)Fe(R), where P = the dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin (OETPP) and R = C6H5, 3,5-C6F2H3, 2,4,6-C6F3H2, or C6F5 or P = the dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and R = C6H5, 2,4,6-C6F3H2, or 2,3,5,6-C6F4H. The first one-electron transfer from (P)Fe(R) to [Ru(bpy)3]3+ (bpy = 2,2‘-bipyridine) leads to an Fe(IV) σ-bonded complex, [(P)FeIV(R)]+, and occurs at a rate which is much slower than the second one-electron transfer from [(P)FeIV(R)]+ to [Ru(bpy)3]3+ to give [(P)FeIV(R)]•2+. The one- or two-electron oxidation of each (OETPP)Fe(R) or (OEP)Fe(R) derivative was also attained by using [Fe(phen)3]3+ (phen = 1,10-phenanthroline) or [Fe(4,7-Me2phen)3]3+ (Me2phen = 4,7-dimethyl-1,10-phenanthroline) as an electron-transfer oxidant. The reorganization energies (kcal mol-1) for the metal-centered oxidation of (P)FeIII(R) to [(P)FeIV(R)]+ increase in the order (OEP)Fe(R) (83 ± 4) ≪ (OETPP)Fe(C6F5) (99 ± 2) < (OETPP)Fe(2,4,6-C6F3H2) (107 ± 2) < (OETPP)Fe(3,5-C6F2H3) (109 ± 3) < (OETPP)Fe(C6H5) (113 ± 3). Each value is significantly larger than the reorganization energies determined for the porphyrin-centered oxidations involving the same two series of compounds, i.e., the second electron transfer of (P)Fe(R). In each case, the first metal-centered oxidation is the rate-determining step for generation of the iron(IV) porphyrin π radical cation. Coordination of pyridine to (OETPP)Fe(C6F5) as a sixth axial ligand enhances significantly the rate of electron-transfer oxidation.

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Generation of a stable .sigma.-bonded iron(IV) porphyrin. Formation and reactivity of [(OETPP)FeIV(C6H5)]n+ (n = 1-3; OETPP = dianion of 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin)

Cited by 22 publications

References 1 publication

Substituent-Induced Perturbation Symmetries and Distortions of meso-tert-Butylporphyrins

Substituent-Induced Perturbation Symmetries and Distortions of meso-tert-Butylporphyrins

Syntheses and Functionalizations of Porphyrin Macrocycles

Electron-Transfer Kinetics for Generation of Organoiron(IV) Porphyrins and the Iron(IV) Porphyrin π Radical Cations

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