One electron oxidation and reduction

Complexes of manganese with the 1,1-dithiolates have been restricted to the (PrSN)3[Mn(i-mnt)3] complex (112) and nitrosyl or carbonyl derivatives, e.g., [7i--CpMn(NO)(S2C==X)] (X = C(CN)C02Et, C(CN)C0NH2, NCN, C(CN)2, or (HNO2) (110, 204, 205). These complexes undergo electrochemical, one-electron oxidations and reductions to afford the neutral or dianionic species. 

In voltametric studies of Co(R2 Jtc)3 in various solvents, a one-electron oxidation and reduction step was detected (75, 76,162). 

A major consideration before the ligand exchange equilibria can be considered with reference to biological systems is the stability of a particular oxidation state in the biological medium. Low-spin complexes undergo rapid one-electron oxidation and reduction. As a biological system operates at a low redox potential, say —0.5 to 0.0 volts, reduced, i.e. low valence, states of the metals are to be expected. The metal complexes, Ru, Os, Rh, Ir, Pd, Pt and Au should be reduced to the metallic state in fact but for the slow speed of this reduction. The metals of Fig. 6 will tend to go to the following redox states ... 

Elastic tunneling spectroscopy is discussed in the context of processes involving molecular ionization and electron affinity states, a technique we call orbital mediated tunneling spectroscopy, or OMTS. OMTS can be applied readily to M-I-A-M and M-I-A-I -M systems, but application to M-A-M junctions is problematic. Spectra can be obtained from single molecules. Ionization state results correlate well with UPS spectra obtained from the same systems in the same environment. Both ionization and affinity levels measured by OMTS can usually be correlated with one electron oxidation and reduction potentials for the molecular species in solution. OMTS can be identified by peaks in dl/dV vs bias voltage plots that do not occur at the same position in either bias polarity. Because of the intrinsic... 

Electrochemical data have been collected for a selection of the antimony OEP and TPP complexes including [Sb(Por)Me2] and [Sb(Por)(R)(OH)] (R = Me, Et). The complexes show one-electron oxidations and reductions at the porphyrin rings. Spectroelectrochemistry indicated that small amounts of antimony(III) products may be formed through a chemical reaction following the first reduction. " ... 

Redox potentials for i-2 were determined in butyronitrile containing O.IM tetra-n-butylammonium perchlorate using a Pt disc electrode at 21. These potentials were measured relative to a saturated calomel electrode using ac voltammetry.(lQ) Both the one electron oxidations and reductions of i-2 exhibited good reversibility. The half-wave potentials for the one-electron oxidation and reduction of i-2, ZnTPP, and two model quinones are given in Table I. 

Rhenium(III) tris-chelates are formed by the reaction of 2-(diphenylphosphinomethyl)-4-methylphenol, PpOH (258a), or 2-diphenylphosphinophenol, P2-OH (258b) with [ReCl3(PPh3)2(CH3CN)] in a 1 3 ratio. [Re(Pi-0)3] is stable as solid and in solutions while [Re(P2-0)3] is easily oxidized in air giving the rhenium(V) 0x0 complex [Re0(P2-0)2(0P2-0]. This behavior is also reflected in the electrochemical behavior of the compounds, where each one well-defined redox couple for one-electron oxidation and reduction steps are observed for both compounds. A second oxidative wave (Re /Re ) is only reversible for [Re(Pi-0)3]. 

The electrochemical oxidation of [ (bpy)2(NH3)Ru 2(/i-0)] releases N2. Oxidation of the ruthenium species initially gives [ (bpy)2(NH3)Ru 2(/i-0)] followed by irreversible five-electron oxidation and H+ loss. The Ru ° complexes [ (bpy)2LRu 2(/i-0)(p-02CMe)2] have been prepared as perchlorate salts for L = im, 1 - and 4-Meim. Structural data for L = 1 -Meim confirm a trans arrangement of imidazole and 0x0 ligands. The complexes exhibit reversible one-electron oxidation and reduction processes. The interaction of [ (bpy)2(H20)Ru 2(/u-0)] " with DNA results in reductive cleavage of the complex to form [Ru(bpy)2(H20)2] and the rate of reaction increases in the presence... 

Radical cation and anion generated from one-electron oxidation and reduction are... 

NEt4][MoO(S-4-tolyl)4] reacts with A-(2-hydroxybenzyl)-2-mercaptoaniline (H3hbma) to yield [NEt4][Mo(hbma)2], the anions of which possess a highly distorted, all-irons, octahedral geometry. Cyclic voltammetry has been used to demonstrate reversible one-electron oxidation and reduction processes for this complex.309... 

For both complexes, reversible metal-centered one-electron oxidations and reductions have been observed. The products of such redox processes have been examined by monitoring the EPR and electronic spectra obtained by controlled-potential electrolysis and, in the case of the molybdenum complex, have been identified as [Mo(IV)0(TMTEC)]+ and [Mo(VI)0(TMTEC)] ions. 

To determine whether ECL is possible, the free energy of the annihilation reaction can be determined from the one-electron oxidation and reduction potentials of the reactant species and can be expressed as... 

Reactivities of a variety of alcohols, ethers, and amides toward hydroxy radicals derived from Fenton s reagent have been compared with those obtained from radiation chemistry in the absence of iron species.728 b Reactivities of different C—H bonds indicate that hydroxyl radical is a strongly electrophilic radical so that electron supply is more important than C—H bond strength in determining its reactivity. Fenton s reagent thus serves as a useful means for studying the one-electron oxidation and reduction of the resulting carbon-centered radicals with iron(II, III) species.73a,b Furthermore, in these systems the addition of copper(II) complexes that can intercept free radicals effectively often leads to enhanced yields of oxidation products.72 73... 

The difference between the first one-electron oxidation and reduction potential is 2.25 0.2 V. 

In electron-transfer theory it is an important postulate that electrons are transferred one by one (Semenov, 1958), which does not mix well with the two-electron centered electronic theory of organic molecules. Interestingly enough, a lively Russian school propagates ideas of organic electron-transfer mechanisms, often in contradiction to currently accepted views (for reviews, see Todres, 1978 Blyumenfel d et al., 1970 Bilevich and Okhlobystin, 1968). This is reminiscent of a period when one-electron oxidants and reductants, e.g. Fe(CN6)3- and metallic sodium, were perfectly acceptable as electrophiles and nucleophiles, respectively (Ingold, 1953). 

In this article, we discuss several early examples of photoinitiated electron transfer reactions. We also follow the development of alternative methods to achieve one-electron oxidation and reduction. This general reaction type, of which the photo-induced reaction is a special case, pervades organic, bio-, and inorganic chemistry. 

A chemistry of cobalt-sulfide-thiolate molecular clusters comparable with that of iron systems has also begun to emerge. Treatment of [Co4( -SPh)6(SPh)4]2- with HS- in acetone affords the octanuclear cluster [Co8(ji4-S)6(SPh)8]4 isolated as its Pr4N+ salt.988 In MeCN solution the complex is red-purple with intense sulfur-core charge transfer bands which obscure the Co" d-d transitions. This behaviour contrasts with that of both mono- and poly-nuclear cobalt"-thiolate complexes, which all display LMCT bands below 440 nm and have well-developed v2 and v3 features. The [Co8(/j4-S6)]4+ core sustains reversible one-electron oxidation and reduction (E]l2 = —0.54, — 1.18 V, MeCN) and chemical reduction with sodium acenaphthylenide in THF gives [Co8(/r4-... 

Weller correlation Empirical correlation for the energy of full charge-transfer exci-plexes relative to the ground-state in n-hexane as a function of the electrochemical one electron oxidation and reduction potentials measured in a polar solvent for the donor (D) and the acceptor (A) involved (see e.g. A. Weller, in The Exciplex , Gordon and Ware eds., Academic Press Inc., N.Y., 1975) ... 

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