One- and Two-Electron Oxidations of Bimetallic Fulvalene Complexes Studied by Voltammetry and IR Spectroelectrochemistry

Geiger, William E.; Atwood, Christopher G.; Chin, Teen T.

doi:10.1007/978-94-011-1628-2_49

Cited by 6 publications

(6 citation statements)

References 27 publications

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“…We assume that this reduction is pyrazine-centered; the very negative peak potential is close to that of free pyrazine ( E 1/2 = −2.6 V) which suggests that σ donation and π-back-bonding are comparable for that diosmium(II) system. The negative reduction potential is also held responsible for the irreversibility due to loss of cyanide. , …”

Section: Discussionmentioning

confidence: 99%

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Hornung¹,

Baumann²,

Kaim³

et al. 1998

Inorg. Chem.

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The pyrazine-bridged diosmium(II) complex {(μ-C4H4N2)[Os(CN)5]2}6- has been synthesized as the hexapotassium salt and was converted to the hexakis(tetrabutylammonium) compound by ion exchange. Its stepwise oxidation to the Os2 IIIOsII and Os2 IIIOsIII states was monitored spectroelectrochemically in acetonitrile/0.1 M Bu4NPF6 in the UV−vis−NIR and IR regions and by EPR. The OsII 2 species exhibits long-wavelength solvatochromic MLCT bands at 14 800 and 18 480 cm-1. The pentaanionic mixed-valent ion has a comproportionation constant K c of 105.8 and is distinguished by several electronic absorptions in the IR region. The bands at 1972, 2480, 4000, 5000, 7170, and 11 900 cm-1 are similar but appreciably lower in energy than those reported for the analogous complex {(μ-C4H4N2)[Os(NH3)5]2}5+. In addition to CN vibrational stretching features shifted on electron transfer there is an additional sharp band only for the 5− ion at 1582 cm-1 which is attributed to a pyrazine ring vibration. The intensity of this band suggests an unsymmetrical situation and thus valence localization on the vibrational time scale. The EPR signals at g ⊥ = 2.0563 and g ∥ = 1.761 point toward excited states lying close to the doublet ground state and to significant metal/cyanide interaction. Compared to the Creutz−Taube ion {(μ-C4H4N2)[Ru(NH3)5]2}5+ and its osmium homologue, the 5− ion described here exhibits a lower degree of metal−metal coupling.

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Section: Discussionmentioning

confidence: 99%

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Hornung¹,

Baumann²,

Kaim³

et al. 1998

Inorg. Chem.

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“…The fact that there are two close, reversible waves indicates that the Fe I Fe II and Fe I Fe I series are stable on the time scale of cyclic voltammetry. Preliminary attempts to synthesize the reduced neutral complex 4 led to decomposition, but further low-temperature studies might be envisaged to examine the electronic structure of the Fe I Fe II mixed valency and the direduced states . The very small separation between the two waves (Δ E = 120 mV) might indicate, however, that the mixed-valence species Fe I Fe II is localized (class II).…”

Section: Discussionmentioning

confidence: 99%

Fulvalenyl Mono- and Diiron Complexes: Photolytic and Electron-Transfer-Induced Substitution of the Benzene Ligands by Phosphines and CO in the Diiron Fulvalenyl Dibenzene Complexes [Fe₂Fv(C₆H₆)₂]^2+/0. Generation of the Average-Valence Species [Fe₂FvL₆]³⁺(L = Phosphine)

et al. 1997

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The bi-sandwich complex [Fe2Fv(C6H6)2]2+(PF6 -)2 (1 2+; Fv = μ2-η5:η5-fulvalenyl, unless noted otherwise) synthesized from biferrocene, was photolyzed with visible light in acetonitrile in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) or bis(diphenylphosphino)methane (dppm) at −15 °C to give [Fe2Fv(dppe)2(NCMe)2]2+(PF6 -)2 (2a 2+) or [Fe2Fv(dppm)2(NCMe)2]2+(PF6 -)2 (2b 2+). The complexes 2a 2+ and 2b 2+ reacted in refluxing 1,2-dichloroethane with CO to give [Fe2Fv(dppe)2(CO)2]2+(PF6 -)2 (3a 2+) and [Fe2Fv(dppm)2(CO)2]2+(PF6 -)2 (3b 2+), and 2a 2+ reacted similarly with PMe3 to give [Fe2Fv(dppe)2(PMe3)]2+(PF6 -)2 (4 2+). The direduced 38-electron (38e) complex 1 reacted at −15 °C with 1 atm of CO to give [Fe2(μ2-η4:η4-Fv)(CO)6] (7) and with PMe3 to give [Fe2Fv(PMe3)4] (9). When Na+PF6 - was present in stoichiometric amounts in THF, these reactions followed a different course and Na+PF6 - induced electron transfer (disproportionation) by irreversibly dislocating ion pairs: the reaction of 1 with 1 atm of CO gave [Fe(η5-Fv)(η6-C6H6), Na+PF6 -] (5), and that with PMe3 gave [Fe2Fv(PMe3)6]2+(PF6 -)2 (8 2+) and the known complex [Fe(PMe3)4] (10). The cyclic voltammograms (CV) of 2a 2+ and 2b 2+ contain irreversible oxidation and reduction waves, but the CVs of 3a 2+ and 3b 2+ showed two close reversible monoelectronic reduction waves (no oxidation wave). The CVs of the hexaphosphine complexes indicated partially or fully irreversible reduction waves, respectively, but two reversible waves at +0.71 and +0.95 V for 4 2+ and +0.70 and +1.08 V for 8 2+ (vs SCE, Pt, DMF, 0.1 M n-Bu4NBF4 −30 °C). The bielectronic reduction of 2a 2+ and the bielectronic oxidation of 4 2+ and 8 2+ using redox reagents led to decomposition, but the monoelectronic oxidation of 4 2+ and 8 2+ using (p-Br-C6H4)3N+SbCl6 - in CH2Cl2 gave the stable mixed-valence trications 4 3+ and 8 3+ , for which the Mössbauer spectra showed delocalized average valency on the Mössbauer time scale. These studies have opened the route to a variety of mono- and diiron fulvalenyl organometallic compounds, confirming the great importance of the presence of Na+PF6 -. This salt can change reaction pathways and, in particular, induce electron-transfer reactions, underlining the extraordinary electronic flexibility of the fulvalenyl ligand and its ability to transfer the electron flow between two metal centers.

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“…In carboxylate-bridged diiron complexes, if the Fe centers are electronically coupled through the carboxylate bridge, the second Fe center is oxidized at potentials more positive than the first, and two one-electron redox features are observed in CVs. If, however, there is little or no electronic coupling, the Fe centers are oxidized at identical or nearly identical potentials, and a two-electron redox wave is observed. , Several homonuclear dimetallic complexes have similar two-electron redox features that are assigned as two sequential one-electron transfers occurring at nearly identical potentials. , In RNR R2, the lack of an observable Fe(II)Fe(III) valence state has been attributed to the first electron transfer occurring at a more negative potential than the second …”

Section: Results and Discussionmentioning

confidence: 99%

“…17,18 Several homonuclear dimetallic complexes have similar two-electron redox features that are assigned as two sequential one-electron transfers occurring at nearly identical potentials. 19,20 In RNR R2, the lack of an observable Fe(II)Fe(III) valence state has been attributed to the first electron transfer occurring at a more negative potential than the second. 21 The CV of 7 shows two oxidation events at 0.12 and 0.44 V (Figure S20).…”

Section: ■ Introductionmentioning

confidence: 99%

Tuning the Diiron Core Geometry in Carboxylate-Bridged Macrocyclic Model Complexes Affects Their Redox Properties and Supports Oxidation Chemistry

et al. 2017

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We introduce a novel platform to mimic the coordination environment of carboxylate-bridged diiron proteins by tethering a small, dangling internal carboxylate, (CH)COOH, to phenol-imine macrocyclic ligands (HPIMICn). In the presence of an external bulky carboxylic acid (RCOH), the ligands react with [Fe(Mes)] (Mes = 2,4,6-trimethylphenyl) to afford dinuclear [Fe(PIMICn)(RCO)(MeCN)] (n = 4-6) complexes. X-ray diffraction studies revealed structural similarities between these complexes and the reduced diiron active sites of proteins such as Class I ribonucleotide reductase (RNR) R2 and soluble methane monooxygenase hydroxylase. The number of CH units of the internal carboxylate arm controls the diiron core geometry, affecting in turn the anodic peak potential of the complexes. As functional synthetic models, these complexes facilitate the oxidation of C-H bonds in the presence of peroxides and oxo transfer from O to an internal phosphine moiety.

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One- and Two-Electron Oxidations of Bimetallic Fulvalene Complexes Studied by Voltammetry and IR Spectroelectrochemistry

Cited by 6 publications

References 27 publications

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Fulvalenyl Mono- and Diiron Complexes: Photolytic and Electron-Transfer-Induced Substitution of the Benzene Ligands by Phosphines and CO in the Diiron Fulvalenyl Dibenzene Complexes [Fe₂Fv(C₆H₆)₂]^2+/0. Generation of the Average-Valence Species [Fe₂FvL₆]³⁺(L = Phosphine)

Tuning the Diiron Core Geometry in Carboxylate-Bridged Macrocyclic Model Complexes Affects Their Redox Properties and Supports Oxidation Chemistry

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One- and Two-Electron Oxidations of Bimetallic Fulvalene Complexes Studied by Voltammetry and IR Spectroelectrochemistry

Cited by 6 publications

References 27 publications

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)5]2}n-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)5]2}n-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Fulvalenyl Mono- and Diiron Complexes: Photolytic and Electron-Transfer-Induced Substitution of the Benzene Ligands by Phosphines and CO in the Diiron Fulvalenyl Dibenzene Complexes [Fe2Fv(C6H6)2]2+/0. Generation of the Average-Valence Species [Fe2FvL6]3+(L = Phosphine)

Tuning the Diiron Core Geometry in Carboxylate-Bridged Macrocyclic Model Complexes Affects Their Redox Properties and Supports Oxidation Chemistry

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Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Spectroelectrochemical Characterization of the Two-Step Redox System {(μ-pz)[Os(CN)₅]₂}ⁿ^-(n= 4, 5, 6; pz = Pyrazine). Similarities and Differences in Relation to the Creutz−Taube System

Fulvalenyl Mono- and Diiron Complexes: Photolytic and Electron-Transfer-Induced Substitution of the Benzene Ligands by Phosphines and CO in the Diiron Fulvalenyl Dibenzene Complexes [Fe₂Fv(C₆H₆)₂]^2+/0. Generation of the Average-Valence Species [Fe₂FvL₆]³⁺(L = Phosphine)