Electron transport via metalloporphyrins

Johnson, Eugene C.; Niem, T.; Doolphin, David

doi:10.1139/v78-229

Cited by 33 publications

(12 citation statements)

References 21 publications

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“…As a consequence, the value of the E 1/2 4-3 decreases about 120 mV when the ES is changed from TBA(PF 6 ) to TBAP. Such a dependence from the ES anion was also observed before by other workers with ZnTPP in CH 2 Cl 2 solutions of the same ES [23,24] We propose instead the following explanation: (i) the -cation formed in the first oxidation process interacts with the SE anion and forms a new species, the ion-pairs {P + (ClO 4 − )} or {P + (PF 6 − )}, where P represents the neutral porphyrin molecule, and (ii) the energy of the HOMO of the {P + (ClO 4 − )} species is higher than that of the HOMO of the {P + (PF 6 − )} species, i.e., the stabilization of P + through ion-pairing increases when the SE anion is changed from ClO 4 − to PF 6 − . The new species adsorbs on the WE surface giving rise to a stabilized surface species; as a consequence, the first oxi- dation peak Ox1 is preceded by the prewave 1 and followed by the postwave 2 shown in Fig.…”

Section: Redox Processes: General Datasupporting

confidence: 86%

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Paliteiro

Sobral

2005

Electrochimica Acta

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A series of three meso-tetra-alkyl porphyrins (H 2 TAPs) were synthesised and their electrochemical properties were studied in dichloromethane containing either tetra-butyl ammonium perclorate (TBAP) or tetra-butyl ammonium hexafluorophosphate TBA(PF 6 ) as supporting electrolyte (SE) by cyclic voltammetry and in situ UV/vis spectroelectrochemistry. Values of E 1/2 for the recorded four redox processes of these porphyrins and of the meso-tetra-phenyl porphyrin (H 2 TPP) on glassy carbon and platinum were measured and compared. The redox data collected on the first oxidation and the first reduction processes predict that the value of (LUMO − HOMO) for the H 2 TAPs is lower than for meso-tetra-phenyl porphyrin and, therefore, that the first Q band of the electronic spectra of the H 2 TAPs is red shifted relatively to the same band in the spectrum of H 2 TPP; this shift was indeed found. The second oxidation process of the H 2 TAPs is influenced by the supporting electrolyte used and the dication then formed is consumed by an irreversible chemical reaction. The species produced in this reaction is irreversibly reduced at a considerably lower potential. The electrochemical and spectroelectrochemical data collected are consistent with the occurrence of structural distortion in the macrocycle rings of the H 2 TAPs.

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Section: Redox Processes: General Datasupporting

confidence: 86%

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Paliteiro

Sobral

2005

Electrochimica Acta

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“…where it was suggested that axial ligation may trigger the elecThe redox properties of metalloporphyrins in general have tron transfer (10). The present studies strongly support this been studied extensively (6), but the studies on ruthenium hypothesis.…”

supporting

confidence: 81%

Synthesis and redox chemistry of octaethylporphyrin complexes of ruthenium(II) and ruthenium(III)

Barley¹,

Becker²,

Domazetis³

et al. 1983

Can. J. Chem.

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. Can. J. Chem. 61, 2389Chem. 61, (1983.The syntheses and characterization of some ncw octaethylporphyrin complexes of ruthenium(l1) and ruthcnium(lll) are described; the complexes are Ru(OEP)(P"BU~)~. Ru(OEP)(CO)L (L = PPh3, PUBu3), [Ru(OEP)(P"BU,)~]B~, and Ru(0EP)-(PnBu3)Br, where OEP is the dianion of octaethylporphyrin. The Ru(OEP)(CO)EtOH complex, 1, which reversibly loscs the ethanol ligand in CHzC12 solution, undergoes a one-equivalent oxidation at the porphyrin ligand to gencratc the cation-radical [Ru(OEP)"(CO)]+; a purple species of 'Azu ground statc, produced electrochemically in perchlorate mcdia, can coordinate bromide to generate a green 'A,, ground state species that also results from oxidation of 1 using bromine. Coordination of pyridine to [Ru(OEP)'+CO]+ yields the Ru(OEP)"(CO)py species that can also be formcd by electrochemical oxidation of Ru(OEP)(CO)py. Addition of tertiary phosphines (PR3) to the cation-radical carbonyl spccics can lead to formation of [RU(OEP)(PR,)~]+, via an internal electron transfcr proccss from Ru(11) to the OEP" that appears to bc triggered by loss of the CO ligand. A reversible one-electron electrochemical oxidation of RU(OEP)(P"BU,)~ at 0.03 V (vs. Ag/AgCI) in CH2CIz also gives the ruthenium(Il1) biphosphine cation, while a furthcr onc-elcctron oxidation at 1.2 V generates [Ru(OEP)'+(P"BU,)~]'+, a ruthenium(lI1) n-cation radical characterized by esr. Thc [Ru(OEP)(P"Bu,),]Br complcx decomposes in the solid state to a mixture of Ru(OEP)(PUBu,)Br, formed together with free phosphine via an intramolecular ligand exchange, and RU(OEP)(P"BU~)~, formed by rcduction of the initial ionic ruthenium (lI1) [Traduit par le journal]

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“…The different ratio of the deprotonated species is attributed to a change in p K a and/or pH of aqueous solutions upon freezing of the EPR sample. 23,24 …”

Section: Resultsmentioning

confidence: 99%

“…The different ratio of the deprotonated species is attributed to a change in pK a and/or pH of aqueous solutions upon freezing of the EPR sample. 23,24 Mossbauer spectra of the pH 2 and 13 samples were recorded at 100 K. For this temperature the magnetic spectra essentially collapsed to doublets. At pH 2, the parameters of the doublet were the isomer shift (δ) 0.14 mm s −1 and the quadrupole splitting (ΔE Q ) 3.59 mm s −1 .…”

Section: ■ Introductionmentioning

confidence: 99%

A “Beheaded” TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pK_a

et al. 2016

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Studies of the new tetra-amido macrocyclic ligand (TAML) activator [FeIII{(Me2CNCOCMe2NCO)2CMe2}OH2]− (4) in water in the pH range of 2–13 suggest its pseudo-octahedral geometry with two nonequivalent axial H2O ligands and revealed (i) the anticipated basic drift of the first pKa of water to 11.38 due to four electron-donating methyl groups alongside (ii) its counterintuitive enhanced resistance to acid-induced iron(III) ejection from the macrocycle. The catalytic activity of 4 in the oxidation of Orange II (S) by H2O2 in the pH range of 7–12 is significantly lower than that of previously reported TAML activators, though it follows the common rate law (v/[FeIII] = kIkII[H2O2][S]/(kI[H2O2] + kII[S]) and typical pH profiles for kI and kII. At pH 7 and 25 °C the rate constants kI and kII equal 0.63 ± 0.02 and 1.19 ± 0.03 M−1 s−1, respectively. With these new values for pKa, kI and kII establishing new high and low limits, respectively, the rate constants kI and kII were correlated with pKa values of all TAML activators. The relations log k = log k0 + α × pKa were established with log k0 = 13 ± 2 and 20 ± 4 and α = −1.1 ± 0.2 and −1.8 ± 0.4 for kI and kII, respectively. Thus, the reactivity of TAML activators across four generations of catalysts is predictable through their pKa values.

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Electron transport via metalloporphyrins

Cited by 33 publications

References 21 publications

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Synthesis and redox chemistry of octaethylporphyrin complexes of ruthenium(II) and ruthenium(III)

A “Beheaded” TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pK_a

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Electron transport via metalloporphyrins

Cited by 33 publications

References 21 publications

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins

Synthesis and redox chemistry of octaethylporphyrin complexes of ruthenium(II) and ruthenium(III)

A “Beheaded” TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pKa

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A “Beheaded” TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pK_a