Chromium(III) porphyrins. Chemical and spectroscopic properties of chloro-meso-tetraphenylporphinatochromium(III) in nonaqueous solutions

Summerville, David A.; Jones, Robert; Hoffman, Brian M.; Basolo, Fred

doi:10.1021/ja00467a012

Cited by 91 publications

(83 citation statements)

References 9 publications

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“…MTPPCl species have favorable binding energies for pyridine coordination via reaction (I). This is known experimentally for CrTPPCl [45]. Although the energy of reaction (II) is unfavorable for Fe, the energy of reaction (I) is sufficiently large that the formation of the bis-pyridine adduct is exothermic.…”

Section: Density Functional Theory Calculationsmentioning

confidence: 65%

Aerobic oxidation of β-isophorone by tetraphenylporphyrin catalysts in pyridine solution

Burns

Huang

Weare

et al. 2015

Journal of Molecular Catalysis A: Chemical

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a b s t r a c tA kinetic study was conducted using five metallo-tetraphenylporphyrins (MTPPs) as catalysts for the aerobic oxidation reaction of ␤-isophorone (␤-IP) to ketoisophorone (KIP). The oxidation reaction catalyzed by MTPPs (M = Cr, Mn, Fe, Co and Cu) was observed over a seven hour period under a range of experimental conditions. Changes in the specificity of conversion of reactant to the product, KIP, and the main side-product, ␣-isophorone (␣-IP), were observed at temperatures ranging from 60 • C to 75 • C, in solvents with varying compositions of pyridine and ␤-IP, with different MTPP catalysts, oxygen gas flow rates, and solution agitation frequencies. Control experiments show that MTPP catalysts modestly increase the rate of KIP formation, but significantly improve specificity through the apparent suppression of ␣-IP formation. Analysis revealed that MnTPP (CH 3 COO − ) produced the highest product specificity ratio [KIP]/ [␣-IP]. Given that all of the metals were in the 3+ oxidation state in this study and there was no observed binding by O 2 to any of the MTPP catalysts, the catalytic mechanism is suggested to involve the binding of ␤-IP to the MTPP metal center. Binding of ␤-IP is most favorable when pyridine is the trans ligand, but ␤-IP is also observed to weakly bind when trans to acetate in the MnTPP adduct. This conclusion is supported by electronic absorption spectroscopy, resonance Raman spectroscopy and density functional theory (DFT) calculations. The role played by the catalyst appears to be the activation of hydrogen abstraction following the substrate's ligation to the metal, rather than the more traditional role of MTPPs as O 2 activation catalysts by ligation of diatomic O 2 . ␤-IP oxidation is an example of a case where the catalyst appears to have a more important role for improving the specificity of the reaction (through decreasing side-product formation) rather than increasing the rate of product formation.

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Section: Density Functional Theory Calculationsmentioning

confidence: 65%

Aerobic oxidation of β-isophorone by tetraphenylporphyrin catalysts in pyridine solution

Burns

Huang

Weare

et al. 2015

Journal of Molecular Catalysis A: Chemical

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“…Except for Cr-TPPCl, all porphyrin dyes, Zn-TPPD [Tokyo Chemical Industry Co., Ltd. (TCI), Tokyo, Japan], TPFPP (TCI), TCPP (TCI), and hemin (TCI) were commercially available and used without further purification. Cr(III)-TPPCl was prepared by a refluxing method published by Adler and coworkers [31]. H 2 TPP (1.0 g, >98.0%, chlorine free, TCI) was dissolved in 300 mL of N,N-dimethylformamide (DMF).…”

Section: Methodsmentioning

confidence: 99%

Dye Modification Effects on TaON for Photocatalytic Hydrogen Production from Water

Hagiwara

Nagatomo

Seto³

et al. 2013

Catalysts

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Modification effects of porphyrin dyes on the photocatalytic activity of tantalum (oxy)nitride (TaON) were investigated. The nitrogen content in tantalum (oxy)nitride was increased by increasing the heat treatment period. The optimized nitridation conditions were found to be calcination at 800 °C for 14 h under a NH 3 gas flow (25 mL min −1). Among the porphyrin dyes examined, pentamethylene bis [4-(10,15,20-triphenylporphine-5-yl) benzoate]-dizinc (II) (Zn-TPPD) showed the most positive effect on the photocatalytic activity of TaON for H 2 production from Na 2 S aqueous solution. From the results of the photocatalytic reaction using various combinations of catalyst components, it was found that the modification dye and PtO x co-catalysts were necessary to achieving photocatalytic H 2 formation. In the PtO x /Zn-TPPD/TaON photocatalyst, the expected charge transfer mechanism was a two-step excitation of both TaON and Zn-TPPD, and the oxidation and reduction sites were TaON and PtO x co-catalyst, respectively. These results indicate that dye modification has the potential to improve the photocatalytic activity of various (oxy)nitride photocatalysts.

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“…The spectrum of a diamagnetic chromium(IV) complex contains wellresolved tetraphenylporphyrin signals in the range 7.7839.08 ppm [12]. Comparison of the corresponding electronic spectrum (maxima and log e) with published data [4,7,15,16] provides evidence for the valence state of Cr(III). Addition of a nearly equimolar amount of imidazole has no effect on the signal of the metal complex and gives rise to fairly narrow singlets with a 1 : 2 integral intensity ratio, assignable to the protons in the 2 and 4,5 positions of the heteroring [17].…”

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confidence: 88%

“…According to [9,10], in aqueous solutions Cr(III) complexes tend to lose the acido ligand localized in the fifth coordination position to give charged bisaqua complexes whose reaction with imidazole gives rise to bisimidazole derivatives. Conductometric and spectral studies [4,13] showed that in organic solvents (acetonitrile, DMSO) coordination of heterocycles involves no dissociation of acido ligand and formation of charged complexes, whereas analysis of the electronic absorption spectra of chromium(III) (acetate)tetraporphyrinate (AcO)CrTPP in toluene made Tipugina and Lomova [8] to suggest that axial coordination involves formation of ion pairs. Figure 1 illustrates the changes in the electronic absorption spectra, produced by addition of imidazole (Im) into a solution of (AcO)CrTPP in ethanol.…”

mentioning

confidence: 99%

“…Evidence for the this conclusion comes from the spectral parameters of octahedral complexes of Cr(III) with porphyrins [4,7,15,16] and the ESR spectra [4] of complexes of (Cl)CrTPP with N-, O-, and S-ligands. Some information is available to show that the acido ligand does not dissociate under conditions of kinetic experiments [4], as well as on laser photolysis of toluene solutions of [18].…”

mentioning

confidence: 99%

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Coordination of Aza Heterocycles with Macroheterocyclic Metal Complexes in Amphiprotic Media: I. Reaction of Imidazole with Chromium(II) (Acetate)tetraphenylpophyrinate

et al. 2005

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Coordination of imidazole with chromium(II) (acetate)tetraphenylpophyrinate involves consecutive substitution of alcohol molecules in the sixth coordination position of the complex. Axial coordination of imidazole produces no charged species.The recent interest in macroheterocyclic complexes generally and in metal porphyrins specifically is explained by their practical importance. Of particular mention is modeling natural biocoordination systems by porphyrin metal complexes. In addition, metal porphyrins are used as catalysts in chemical engineering. Considerable researcher's attention has been given to porphyrin complexes of transition metals, such as iron(II), iron(III), chromium(III), and cobalt(III) [1,2]. Notwithstanding the fact that these complexes contain an axial acido ligand, the coordination ability of the metal ion in them is still unexhausted and can coordinate additional ligands (or solvent molecules) that possess electron-donor properties.The choice of chromium(III) porphyrin complexes as objects for study was motivated by their weaker tendency to formation of m-oxo dimers [1] and also by the fact that Cr(III), unlike Fe(II) and Fe(III), has a stable spin state unaffected by coordination of an axial ligand. It should be noted that chromium(III) porphyrinates are only appreciably soluble in sufficiently solvating solvents whose molecules occupy the sixth coordination site of the octahedral complex. Among organic solvents the most interesting are alcohols as low-molecular models most similar to the macromolecular surrounding of biological macrocyclic complexes [3] in terms of polarity, polarizability, hydrophilic3lypophilic balance, and amphiprotic nature.The thermodynamics, kinetics, and mechanism of axial coordination with chromium(III) porphyrin complexes were studied in low-polarity aromatic hydrocarbons, halohydrocarbons, and other solvents [438] unable to specific interactions and not possessing proton-donor properties. Processes that occur in water, alcohols, and other amphiprotic solvents have scarcely been studies.The present work deals with the regularities of axial ligand exchange in porphyrin complexes of transition metals in alcohols.The first step of the research on the mechanisms of ligand exchange in transition metal complexes involves assessment of the starting and final states in solutions. Ligand exchange in chromium(III) porphyrin complexes has been studied in [4312]. According to [9,10], in aqueous solutions Cr(III) complexes tend to lose the acido ligand localized in the fifth coordination position to give charged bisaqua complexes whose reaction with imidazole gives rise to bisimidazole derivatives. Conductometric and spectral studies [4,13] showed that in organic solvents (acetonitrile, DMSO) coordination of heterocycles involves no dissociation of acido ligand and formation of charged complexes, whereas analysis of the electronic absorption spectra of chromium(III) (acetate)tetraporphyrinate (AcO)CrTPP in toluene made Tipugina and Lomova [8] to suggest that axial coordinati...

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Chromium(III) porphyrins. Chemical and spectroscopic properties of chloro-meso-tetraphenylporphinatochromium(III) in nonaqueous solutions

Cited by 91 publications

References 9 publications

Aerobic oxidation of β-isophorone by tetraphenylporphyrin catalysts in pyridine solution

Aerobic oxidation of β-isophorone by tetraphenylporphyrin catalysts in pyridine solution

Dye Modification Effects on TaON for Photocatalytic Hydrogen Production from Water

Coordination of Aza Heterocycles with Macroheterocyclic Metal Complexes in Amphiprotic Media: I. Reaction of Imidazole with Chromium(II) (Acetate)tetraphenylpophyrinate

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