Redox Chemistry Of Complexes Research Articles

Ebselen, a Selenium-Containing Redox Drug, Releases Zinc from Metallothionein

Selenium compounds oxidize the thiolate ligands in the zinc clusters of metallothionein and release zinc. This chemistry defines new cellular targets for biological forms of selenium and suggests important interactions between zinc and selenium, two biologically essential elements. In the course of delineating the redox chemistry of biological zinc complexes with thiolate ligands, we have found that the non-toxic experimental drug ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) releases zinc from metallothionein. The reaction follows a 1:1 stoichiometry for thiols, is very rapid (t1/2< 1 min), and proceeds through the opening of the isoselenazol ring and formation of a selenodisulfide with metallothionein. Despite the fast reaction of ebselen with glutathione (t1/2< 1 s), which proceeds past the stage of the selenodisulfide adduct to the selenol and diselenide derivatives, ebselen reacts with MT even in the presence of glutathione, suggesting that it can also react with MTin vivo.These findings reveal a new mode of action for ebselen and therefore suggest therapeutic applications in zinc-related medical disorders as well as a possible role of biological selenium compounds in zinc metabolism.

Nitrogen atom transfer and redox chemistry of terpyridyl phosphoraniminato complexes of osmium (IV)

Rapid reactions occur between [Os VI(tpy)(Cl) 2(N)]X (X = PF 6 −, Cl −, tpy = 2,2′:6′,2″-terpyridine) and aryl or alkyl phosphi nes (PPh 3, PPh 2Me, PPhMe 2, PMe 3 and PEt 3) in CH 2Cl 2 or CH 3CN to give [Os IV(tpy)(Cl) 2(NPPh 3)] + and its analogs. The reaction between trans-[Os VI(tpy)(Cl) 2(N)] + and PPh 3 in CH 3CN occurs with a 1:1 stoichiometry and a rate law first order in both PPh 3 and Os VI with k(CH 3CN, 25°C) = 1.36 ± 0.08 × 10 4 M − s −1. The products are best formulated as paramagnetic d 4 phosphoraniminato complexes of Os IV based on a room temperature magnetic moment of 1.8 μ B for trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6), contact shifted 1H NMR spectra and UV-Vis and near-IR spectra. In the crystal structures of trans-[Os IV(tpy)(Cl) 2( NPPh 3)](PF 6)·CH 3CN (monoclinic, P2 1/ n with a = 13.384(5) Å, b = 15.222(7) Å, c = 17.717(6) Å, β = 103.10(3)°, V = 3516(2) Å 3, Z = 4, R w = 3.40, R w = 3.50) and cis-[Os IV(tpy)(Cl) 2(NPPh 2Me)]-(PF 6)·CH 3CN (monoclinic, P2 1/ c, with a = 10.6348(2) Å, b = 15.146(9) ÅA, c = 20.876(6) Å, β = 97.47(1)°, V = 3334(2) Å 3, Z = 4, R = 4.00, R w = 4.90), the long Os-N(P) bond lengths (2.093(5) and 2.061(6) Å), acute Os-N-P angles (132.4(3) and 132.2(4)°), and absence of a significant structural trans effect rule out significant Os-N multiple bonding. From cyclic voltammetric measurements, chemically reversible Os V/IV and Os IV/III couples occur for trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) in CH 3CN at +0.92 V (Os V/IV) and −0.27 V (Os IV/III) versus SSCE. Chemical or electrochemical reduction of trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) gives isolable trans-Os III(tpy)(Cl) 2(NPPh 3). One-electron oxidation to Os V followed by intermolecular disproportionation and PPh 3 group transfer gives [Os VI(tpy)Cl 2(N)] +, [OS III(tpy)(Cl) 2(CH 3CN)] + and [Ph 3=N=PPh 3] + (PPN +). trans-[Os IV(tpy)(Cl) 2(NPPh 3)](PF 6) undergoes reaction with a second phosphine under reflux to give PPN + derivatives and Os II(tpy)(Cl) 2(CH 3CN) in CH 3CN or Os II(tpy)(Cl) 2(PR 3) in CH 2Cl 2. This demonstrates that the Os VI nitrido complex can undergo a net four-electron change by a combination of atom and group transfers.

Redox chemistry of copper acetate binuclear complexes in acetic acid-methanol mixture as solvent

The redox chemistry of the photochemically generated bioinorganic model (CH 3COO) 2Cu II Cu I(OOCCH 3) 2 and the parent species (CH 3COO) 2Cu IICu II(OOCCH 3) 2 (complex I) are reported. The purpose is to achieve a more complete physicochemical characterization of the acetate binuclear copper complex and consequently a closer evaluation of its behaviour as a model of type III Cu sites in cuproproteins. Complex I may be sequentially reduced (broad not resolved peaks around −0.2 and −0.4 V) and reoxidized (peaks at 0.16 and 0.36 V), but in competition with a thermal disproportionation to Cu II and Cu 0. Controlled potential electrolysis (CPE) at −0.4 V measures quantitatively the overall reduction process including disproportionation and involves four electrons per mole of initial complex I. Structural changes seem to play a role in the oxidation-reduction processes as suggested by ip/√v vs v studies (Nicholson and Shain's criteria), and they make the processes irreversible. The mixed-valence Cu II-Cu I species could not be produced by CPE at any voltage before the second reduction peak; however, its electrochemical generation by pulses at −0.4 V render direct experimental evidence that the reduction process is sequential. The voltammograms of the Cu II-Cu I species generated photochemically are more complicated: the reduction and oxidation peaks are centered at −0.2 and 0.0 V, respectively. The species Cu II-Cu II originated from the oxidation of this mixed valence complex, called as complex II, shows similarities and differences with complex I. The results are discussed in relation to the structure stability and to the copper interactions in the binuclear species considered as models for the copper protein centers.

Reductive Electrochemistry of Rhodium Porphyrins. Disproportionation of Intermediary Oxidation States

The reduction of rhodium(III) porphyrins in polar aprotic solvents is a two-electron irreversible reaction yielding directly the Rh(I) complex. The cause of this irreversibility is not the metal−metal dimerization of the initially formed Rh(II) complex as believed earlier but rather deligation which generates a secondary Rh(II) species easier to reduce than the starting Rh(III) porphyrin. This is confirmed by the fact that sterically encumbered porphyrins, such as those bearing cross-trans basket-handle superstructures which forbid the approach of two molecules at bonding distance, exhibit the same behavior as simple rhodium porphyrins. The occurrence of such an ECE−disproportionation process, seldom observed in the redox chemistry of metallo-porphyrins or similar complexes, is probably related to the tendency of the rhodium atom to shift out of the porphyrin plane, particularly at the Rh(I) oxidation state. It is remarkable that strong and soft ligands, e.g., tertiary phosphines, annihilate the dispropor...

Reactions of cationic dinuclear molybdenum complexes containing ?-sulfido and ?-thiolate ligands

Cationic dinuclear molybdenum complexes with bridging sulfido and thiolate ligands of the formula [(CpMo)2(µ-S2CH2)(µ-S)(µ-SR)]− have been found to show extensive reactivity with molecular hydrogen and with organic molecules that results in the cleavage of C-C, C-N, and C-O bonds. The scope of the reactivity and mechanistic information are reviewed in this paper, and the potential relevance of the reactions to those of heterogeneous molybdenum sulfide catalysts in the hydrotreating process is discussed. Studies of the complex redox chemistry and of the electrophilic and nucelophilic sites within the dinuclear derivatives provide an important basis for understanding the bond cleavage reaction mechanisms, and these topics are also reviewed here.

The Redox Chemistry of Niobium(V) Fluoro and Oxofluoro Complexes in LiF‐NaF‐KF Melts

The electrochemical behavior of niobium(V) fluoro and oxofluoro complexes in eutectic LiF‐NaF‐KF (FLINAK) melts at 700°C has been studied by cyclic voltammetry. The fluoro complexes , introduced into the melt by the addition of , can be reduced to niobium metal in two reversible steps involving one and four electrons, respectively. At 700°C the diffusion constants of the fluoro niobate complexes involved in these reduction steps, i.e., and , were determined to be and , respectively. Titration with equivalent amounts of oxide ions, introduced as , leads to a conversion of to oxofluoro complexes of the type and . At 700°C the conversion of to is not complete, and the degree of conversion is shown to depend strongly on temperature. Thus, at 645°C the conversion is more nearly complete than at 700°C, while the presence of complexes cannot be identified in cyclic voltammograms obtained at 795°C. It is concluded that the degree of conversion decreases with increasing temperature. At molar ratios equal to three, electroactivity is still observed in the melt, indicating the presence of solute species. The products of reduction of the oxofluoro complexes have not been identified because the reduction of ions cannot be obtained without simultaneous reduction of ions, and at molar ratios exceeding two, no deposits are obtained. The reduction of the oxofluoro complex , and complexes formed at molar ratios exceeding two always proceed in one step.

Coordination and Redox Chemistry of Substituted-Polypyridyl Complexes of Ruthenium.

The complexes [Ru(tpy)(acac)(Cl)], [Ru(tpy)(acac)(H(2)O)](PF(6)) (tpy = 2,2',2"-terpyridine, acacH = 2,4 pentanedione) [Ru(tpy)(C(2)O(4))(H(2)O)] (C(2)O(4)(2)(-) = oxalato dianion), [Ru(tpy)(dppene)(Cl)](PF(6)) (dppene = cis-1,2-bis(diphenylphosphino)ethylene), [Ru(tpy)(dppene)(H(2)O)](PF(6))(2), [Ru(tpy)(C(2)O(4))(py)], [Ru(tpy)(acac)(py)](ClO(4)), [Ru(tpy)(acac)(NO(2))], [Ru(tpy)(acac)(NO)](PF(6))(2), and [Ru(tpy)(PSCS)Cl] (PSCS = 1-pyrrolidinedithiocarbamate anion) have been prepared and characterized by cyclic voltammetry and UV-visible and FTIR spectroscopy. [Ru(tpy)(acac)(NO(2))](+) is stable with respect to oxidation of coordinated NO(2)(-) on the cyclic voltammetric time scale. The nitrosyl [Ru(tpy)(acac)(NO)](2+) falls on an earlier correlation between nu(NO) (1914 cm(-)(1) in KBr) and E(1/2) for the first nitrosyl-based reduction 0.02 V vs SSCE. Oxalate ligand is lost from [Ru(II)(tpy)(C(2)O(4))(H(2)O)] to give [Ru(tpy)(H(2)O)(3)](2+). The Ru(III/II) and Ru(IV/III) couples of the aqua complexes are pH dependent. At pH 7.0, E(1/2) values are 0.43 V vs NHE for [Ru(III)(tpy)(acac)(OH)](+)/[Ru(II)(tpy)(acac)(H(2)O)](+), 0.80 V for [Ru(IV)(tpy)(acac)(O)](+)/[Ru(III)(tpy)(acac)(OH)](+), 0.16 V for [Ru(III)(tpy)(C(2)O(4))(OH)]/[Ru(II)(tpy)(C(2)O(4))(H(2)O)], and 0.45 V for [Ru(IV)(tpy)(C(2)O(4))(O)]/[Ru(III)(tpy)(C(2)O(4))(OH)]. Plots of E(1/2) vs pH define regions of stability for the various oxidation states and the pK(a) values of aqua and hydroxo forms. These measurements reveal that C(2)O(4)(2)(-) and acac(-) are electron donating to Ru(III) relative to bpy. Comparisons with redox potentials for 21 related polypyridyl couples reveal the influence of ligand changes on the potentials of the Ru(IV/III) and Ru(III/II) couples and the difference between them, DeltaE(1/2). The majority of the effect appears in the Ru(III/II) couple. ()A linear correlation exists between DeltaE(1/2) and the sum of a set of ligand parameters defined by Lever et al., SigmaE(i)(L(i)), for the series of complexes, but there is a dramatic change in slope at DeltaE(1/2) approximately -0.11 V and SigmaE(i)(L(i)) = 1.06 V. Extrapolation of the plot of DeltaE(1/2) vs SigmaE(i)(L(i)) suggests that there may be ligand environments in which Ru(III) is unstable with respect to disproportionation into Ru(IV) and Ru(II). This would make the two-electron Ru(IV)O/Ru(II)OH(2) couple more strongly oxidizing than the one-electron Ru(IV)O/Ru(III)OH couple.

Crystal structures of trans-[Ru(dppe) 2(CO)(Cl)](BF 4)·2(toluene) and trans-[Ru(dppm) 2(CO)(Cl)](BF 4)·CH 2Cl 2: a study of the steric and electronic ligand effects of trans-positioned diphosphine ligands

Single-crystal X-ray diffraction studies were carried out on the complexes trans-[Ru(dppe) 2(CO)(Cl)](BF 4) ·2(toluene) ( 1) (where dppe = 1,2-bis(diphenylphosphino)ethane) and trans-[Ru(dppm) 2(CO)(Cl)](BF 4) ·CH 2Cl 2 ( 2) (where dppm = bis(diphenylphosphino)methane). Complex 1 crystallizes in the orthorhombic space group P2 12 12 with a = 14.366(3), b = 17.075(3), c = 12.433(2) A ̊ , V = 3049.8(10) A ̊ 3 and Z = 2 . The structure was refined to R = 3.02% for 3233 reflections above 6σ ( R = 4.46% for all 3991 point-group independent data); the Ru-cation lies on a site of C 2 symmetry, leading to disorder of the Cl and CO ligands. Complex 2 crystallizes in the orthorhombic space group Pna2 1, with a = 22.425(7), b = 11.515(4), c = 19.511(10) A ̊ , V = 5038(3) A ̊ 3 and Z = 4 . The structure was refined to R = 4.43% for 4770 reflections above 6σ ( R = 7.09% for all 6631 point-group independent data). The crystal structure data suggest increased intramolecular interligand interactions with the trans-bis(dppe) complexes relative to the trans-bis(dppm) complexes. In order to furth assess the steric ligand effects of dppm and dppe on the redox chemistry of ruthenium complexes, the electrochemical data for complexes 1 and 2 as well as for trans-Ru(dppe) 2(Cl) 2 and trans-Ru(dppm) 2(Cl) 2 were analyzed. The E pa value for the oxidation of complex 1 was more positive than the E pa value for the oxidation of complex 2; similarly, the E 1 2 value for the oxidation of trans-Ru(dppe) 2(Cl) 2 was more positive than the E 1 2 value for the oxidation of trans-Ru(dppm) 2(Cl) 2. The increase in the redox potentials for the oxidation of the dope complexes may be due to the enhanced intramolecular interligand interactions of the dppe ligands, which is in agreement with the crystal structure data.

Redox chemistry and substitution reactions of the μ-cyanoalkylidene complexes [Fe 2(CO) 2(cp) 2( μ-CO){ μ-C(CN) (X)}] n+ ( n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH 2CH = CH 2, PEt 2, or NC 5H 10; n = 1, X = PMe 2Ph)

Electrochemistry of the μ-cyanoalkylidene complexes [Fe 2(CO) 2(cp) 2( μ-CO){ μ-C(CN)(X)}] n+ ( n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH 2CH=CH 2, PEt 2, piperidinyl; n = 1, X = PMe 2Ph) in nonaqueous solutions shows a one-electron reduction to the corresponding paramagnetic monoanions, which have been characterized by EPR spectroscopy. The presence of the positive charge in [Fe 2(CO) 2(cp) 2(μ-CO){μ-C(CN)(PMe 2Ph)}] + makes the one-electron addition significantly easier than to the neutral complexes. None of the 19-electron anions are fully stable and all undergo slow decomposition reactions, the rates of which are a function of the X substituent. Access to the radical anion intermediates [Fe 2(CO) 2(cp) 2(μ-CO){μ-C(CN)(X)}] − does not trigger Electron Tra Chain catalytic substitution reactions of CO by phosphines, but allows these reactions to be successfully carried out by different methods, such as chemical reduction, CO photolysis and use of Me 3NO. The CO-substituted derivatives [Fe 2(cp) 2(CO)(PMe 2Ph)(μ-CO){μC(CN)(X) (X = CN, H, SMe) and [Fe 2(cp) 2( μ-CO)( μ-dppm){ μ-C(CN)(X)}], (X = H, CN; dppm = Ph 2PCH 2PPh 2) were obtained. The one-electron reduction of the monophosphine-substituted complexes is fully irreversible and occurs at potentials 0.3–0.4 V more negative than those of the corresponding precursors. The different methods for promoting CO displacement in the μ-alkylidene complexes have been compared; the photolytic method affords the highest yields.

Structure and Redox Chemistry of Analogous Nickel Thiolato and Selenolato Complexes: Implications for the Nickel Sites in Hydrogenases

The syntheses, structures, and redox properties of isomorphous Ni(I1) thiolato and selenolato complexes of the tridentate ligands bis(2-(hydrochalcogeno)ethyl)methylamines are reported. Reaction of Ni(0Ac)z with bis(2mercaptoethy1)methylamine leads to the formation of a dimeric complex, bis{ [@-2-mercaptoethyl)(2-mercaptoethyl)methylaminato(2-)]nickel(II)}, [Ni(l)]2. This complex contains planar, diamagnetic Ni(I1) centers ligated by a tertiary amine N-donor atom, a terminal thiolate, and two thiolates that bridge to the second Ni center in the dimer. Crystals of [Ni(l)]2 form in orthorhombic space group h a 2 1 with cell dimensions a = 19.695(2) 8, b = 6.042(2) 8, c = 13.463(3) 8, V = 1602(1) A3, and Z = 4. Reaction of Ni(0Ac)p with bis(2-(hydroseleno)ethy1)methylamine results in the formation of a structurally analogous dimeric complex, bis([@-2-(hydroseleno)ethyl)(2-(hydroseleno)ethyl)methylaminato(2-)]nickel(II)}, [Ni(2)]2, where all of the chalcogenolate donors are selenolates. Crystals of [Ni(2)]2 are isomorphous with those of [Ni(l)]z, with a = 20.040(8) 8, b = 6.265(2) 8, c = 13.590(5) 8, and V = 1706(2) A3, One-electron oxidation of either dimeric complex leads to the formation of radical cations, which exhibit EPR spectra consistent with S = l/2 radicals. For [Ni(l)]2+ the g values observed (gx = 2.20, g, = 2.14, g, = 2.02) are essentially identical to those observed for a reduced and catalytically viable redox state of Fe,Ni hydrogenases (gx = 2.20, g, = 2.14, g, = 2.01). The substitution of Sefor S-donors in [Ni(2)]2 does not alter the observed g values much (gx = 2.23, g, = 2.14, g, = 2.05) but leads to the observation of 77Se hyperfine coupling (A, = 129 G) that indicates that the molecular orbital containing the unpaired spin is largely Se in character (54%). Reaction of either dimeric complex with CNleads to the formation of mononuclear trans-dichalcogenolate complexes, [Ni(l)CN]and [Ni(2)CN]-. Exposure of [Ni(l)CN]to 0 2 leads to the quantitative formation of a monosulfinato complex. In contrast, the selenolato complex does not react with 0 2 under the same conditions. The role of selenocysteinate ligation in Fe,Ni,Se hydrogenases is discussed in view of this chemistry.

A redox-based mechanism for the neuroprotective and neurodestructive effects of nitric oxide and related nitroso-compounds.

Congeners of nitrogen monoxide (NO) are neuroprotective and neurodestructive. To address this apparent paradox, we considered the effects on neurons of compounds characterized by alternative redox states of NO: nitric oxide (NO.) and nitrosonium ion (NO+). Nitric oxide, generated from NO. donors or synthesized endogenously after NMDA (N-methyl-D-aspartate) receptor activation, can lead to neurotoxicity. Here, we report that NO.- mediated neurotoxicity is engendered, at least in part, by reaction with superoxide anion (O2.-), apparently leading to formation of peroxynitrite (ONOO-), and not by NO. alone. In contrast, the neuroprotective effects of NO result from downregulation of NMDA-receptor activity by reaction with thiol group(s) of the receptor's redox modulatory site. This reaction is not mediated by NO. itself, but occurs under conditions supporting S-nitrosylation of NMDA receptor thiol (reaction or transfer of NO+). Moreover, the redox versatility of NO allows for its interconversion from neuroprotective to neurotoxic species by a change in the ambient redox milieu. The details of this complex redox chemistry of NO may provide a mechanism for harnessing neuroprotective effects and avoiding neurotoxicity in the central nervous system.

Orthogonal Ru II(bpy) 3 complexes in meso-substituted porphyrins

The synthesis and characterization of mono- and bis- meso-substituted porphyrins, where the substituents are bipyridine (bpy) groups are described. Treatment of these new porphyrins with an excess of cis-RuCl 2(bpy) 2 gives rise to their respective mono- and bis-Ru II(bpy) 3 complexes. These ruthenium porphyrin complexes all exist as a number of structural isomers and this is reflected in both the proton and carbon NMR spectra. The cyclic voltammetry of these redox active systems was examined and is reported herein. The cyclic voltammetry for the ruthenium porphyrins is complex, with the usual two oxidation and two reduction waves of porphyrins mixing with the three reduction waves of the porphyrin bound Ru II(bpy) 3 and the single oxidation wave seen for the Ru II/Ru III couple. In the case of the mono-ruthenium porphyrin, this complex redox chemistry results in the presence of a reversible two-electron reduction, along with the other redox processes. The bis-ruthenium porphyrin has an even more complex redox chemistry. However, the first ligand-based reduction wave in both the mono- and bis-substituted complexes, occur at more negative potentials than those in, simple free, Ru II(bpy) 3.

Redox chemistry of trinuclear complexes possessing a hexathiolatomolybdate(IV) core: in situ syntheses, characterization and geometry optimization

The trinuclear heterobimetallic clusters [(Ph3P)Cu(µ-SR)3Mo(µ-SR)3Cu(PPh3)](R = C6H4Me-4 2, C6H4F-4 3, C6H4Cl-4 4 or C6H4Br-4 5) have been found to undergo reversible one-electron reductions. The reduction potential is sensitive to the para substituent on the thiolate and has been correlated with the electron-donating properties of the substituent. In addition, 2 undergoes a reversible one-electron oxidation. According to EPR measurements, the oxidation of 2 is molybdenum-based. Geometry optimizations based on density functional theory of the oxidized and reduced model cluster [(H3P)Cu(µ-SH)3Mo(µ-SH)3Cu(PH3)], assuming retention of the D3 point-group symmetry, have shown that both redox processes will lead to an elongation of the Mo–Cu vector. Reduction of the central molybdenum fragment will decrease the strength of the Cu to Mo donor bond. Oxidation of the central molybdenum fragment will result in a decrease of electrostatic interaction with the [(H3P)CuCu(PH3)]2+ fragment. The reaction of 2 with NOBF4 results in oxidation of the cluster. The IR spectrum of the diamagnetic reaction product shows a band at 1657 cm–1 suggesting the presence of co-ordinated NO–. Further evidence is provided by 14N NMR spectroscopy. The reactions of 2 and 5 with arenediazonium salts result in degradation of the clusters, with the liberation of organic sulfides and disulfides, suggesting the involvement of free thiyl radicals.

Synthesis, structure and redox chemistry of ferrocenylsilylmethylidinetricobaltnonacarbonyl complexes, FcSi(R) 2CCo 3(CO) 9, 1,1′-Fc′[Si(R) 2CCo 3(CO) 9] 2 (R = Me, Et, Ph) and their derivatives

Reaction between the ferrocenyl silanes FcSiR 2H and 1,1′-Fc′[SiR 2H] 2 (R = Me, Et, Ph) and HCCo 3(CO) 9 gives the corresponding ferrocenylsilylmethylidinetricobaltnonacarbonyl complexes FcSi(R) 2CCo 3(CO) 9 and 1,1′-Fc′[Si(R) 2CCO 3(CO) 9] 2 in good yield. Spectroscopic data include 29Si NMR. The crystal structure of 1,1′-Fc′[Si(Me) 2CCo 3(CO) 9] 2 has been determined by an X-ray diffraction study. Thermal and electron-transfer catalysed substitution reactions with Lewis bases were successful except for the cluster 1,1′-Fc′[Si(Ph) 2CCo 3(CO) 9] 2, where an unusual cleavage of the FcSi bond takes place. Electrochemical and ESR studies of the complexes FcSi(R) 2CCo 3(CO) 9 and 1,1′-Fc′[Si(R) 2CCo 3(CO) 9] 2 (R = Me, Ph) showed a one-electron oxidation centred on the ferrocenyl moiety and a one- or two-electron reduction dependent on the number of CCo 3 redox centres. The observed electrochemistry is consistent with electrochemically non-interacting redox centres. Chemical oxidation of FcSi(Me) 2CCo 3(CO) 9, 1,1′-Fc′[Si(Me) 2CCo 3(CO) 9] 2 and FcSi(Me) 2CCo 3(CO) 8L (L = P(OMe) 3, PPh 3, PCy 3) gave the respective monocations, whereas oxidation of FcSi(Me) 2CCo 3(CO) 7 [P(OMe) 3] 2 produced a dication.

A fast-kinetic investigation of the redox chemistry of iridium chloride complexes using pulse radiolysis

Reactions initiated by OH radicals or e - aq in aqueous IrCl 3- 6 solutions were studied by electron pulse radiolysis using a 600 keV Febetron electron accelerator. Solutions of IrCl 3- 6 were made basic by adding Na 2CO 3; using the carbonate competition method, we find the rate constant for the reaction of OH with IrCl 3- 6 to be 4.7 × 10 9 M -1 s -1. The product IrCl 2- 6 disappears rapidly in N 2O-saturated basic solution or in neutral N 2-saturated solution (N 2O absent) but is nearly inert in neutral solution with H 2O present. We find that IrCl 2- 6 reacts rapidly with hydrogen peroxide in basic media, as confirmed on the benchtop and by stopped-flow kinetics. We therefore infer that reaction with HO - 2 may account for the loss of IrCl 2- 6 under basic conditions. Since e - aq reduces Ir(III) chloride to the Ir(II) state with a rate constant of 6.1 × 10 9 M -1 s -1, we suggest that loss of Ir(IV) in neutral deaerated solution without added N 2O may involve electron transfer from Ir(II). Loss of Ir(IV) in aerated solution is attributed to reduction by the superoxide ion, O - 2. Kinetic simulation of the system on the model described gives good agreement with our experimental results.

Redox chemistry of complexes of nickel(II) with some biologically important peptides in the presence of reduced oxygen species: An ESR study

The reactions between some Ni(II) oligopeptides (Gly-His-Lys, (Gly) 4, Asp-Ala-His-Lys, Gly-Gly-His, βAla-His, and serum albumin) and reduced oxygen species have been characterized by spin-trapping experiments using DMPO and Me 2SO. Most of the peptides possessed superoxide dismutase- and catalase-like activities leading to the formation of either oxene [NiO] 2+ or, in the case of βAla-His, hydroxyl radicals. Both these species may affect DNA integrity through distinct mechanisms.

Redox and reaction chemistry of (octaethylporphyrinato) ruthenium-phenyl complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRedox and reaction chemistry of (octaethylporphyrinato) ruthenium-phenyl complexesJeffery W. Seyler and Charles R. LeidnerCite this: Inorg. Chem. 1990, 29, 19, 3636–3641Publication Date (Print):September 1, 1990Publication History Published online1 May 2002Published inissue 1 September 1990https://doi.org/10.1021/ic00344a004RIGHTS & PERMISSIONSArticle Views90Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (679 KB) Get e-Alerts Get e-Alerts

Redox chemistry of iron picolinate complexes and of their hydrogen peroxide and dioxygen adducts

In aprotic solvents the bis(picolinato)iron(II) [Fe(PA) 2 ] and (2,6-pyridinedicarboxylato)iron(II) [Fe(DPA)] complexes react with hydrogen peroxide and with dioxygen to form a series of monooxygen and dioxygen intermediates and adducts [(PA) 2 FeOFe(PA) 2 (1), (PA) 2 Fe(OO), (PA) 2 FeOFe(PA) 2 •HOOH (2), and their analogues with Fe(DPA)]. The electron-transfer chemistries of the complexes and of their oxygenated products have been characterized by cyclic voltammetry, controlled-potential electrolysis, and rotated ring-disk voltammetry. These results in combination with UV-visible spectrophotometric and magnetic measurements have been used to develop a self-consistent mechanism for the formation of (PA) 2 FeO(OO)Fe(PA) 2 (3) from (PA) 2 FeOFe(PA) 2 (1) and HOOH and for its transformation of methylene carbons to ketones. In dimethylformamide, species 3 (formed from 1 and HOOH) spontaneously decomposes to singlet dioxygen ( 1 O 2 ) and 1

ChemInform Abstract: Redox Reactions of Osmium Porphyrins.

AbstractA variety of experimental techniques is used to study the redox chemistry of Os complexes of porphyrins such as octaethylporphyrin or tetraphenylporphyrin in order to clarify the extent to which the various states are interconvertible.

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

The syntheses and characterization of some new octaethylporphyrin complexes of ruthenium(II) and ruthenium(III) are described; the complexes are Ru(OEP)(P″Bu3)2, Ru(OEP)(CO)L (L = PPh3, P″Bu3), [Ru(OEP)(P″Bu3)2]Br, and Ru(OEP)(P″Bu3)Br, where OEP is the dianion of octaethylporphyrin. The Ru(OEP)(CO)EtOH complex, 1, which reversibly loses the ethanol ligand in CH2Cl2 solution, undergoes a one-equivalent oxidation at the porphyrin ligand to generate the cation-radical [Ru(OEP)•+(CO)]+; a purple species of 2A2u ground state, produced electrochemically in perchlorate media, can coordinate bromide to generate a green 2A1u 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 formed by electrochemical oxidation of Ru(OEP)(CO)py. Addition of tertiary phosphines (PR3) to the cation-radical carbonyl species can lead to formation of [Ru(OEP)(PR3)2]+, via an internal electron transfer process from Ru(II) to the OEP•+ that appears to be triggered by loss of the CO ligand. A reversible one-electron electrochemical oxidation of Ru(OEP)(P″Bu3)2 at 0.03 V (vs. Ag/AgCl) in CH2Cl2 also gives the ruthenium(III) biphosphine cation, while a further one-electron oxidation at 1.2 V generates [Ru(OEP)•+(P″Bu3)2]2+, a ruthenium(III) π-cation radical characterized by esr. The [Ru(OEP)(P″Bu3)2]Br complex decomposes in the solid state to a mixture of Ru(OEP)(P″Bu3)Br, formed together with free phosphine via an intramolecular ligand exchange, and Ru(OEP)(P″Bu3)2, formed by reduction of the initial ionic ruthenium(III) cation with the phosphine that appears as [P″Bu3Br]Br.