Oxidized forms, electrons

Many of the problems and misconceptions occurring for dithiolene compounds are related to the fact that the ligands are redox-active and can be oxidized to monoanionic radicals. Typical examples for this phenomenon are the mono and diradical complexes [Fe ( "bdt )( "bdt)(PMe3)] (9) and [Fe ( "bdf)2(PMe3)]-" (10) for which bdt and bdt are tcrt-butyl-dithiolene and its one-electron oxidized form. Originally, these and other bdt derivatives had been described as... 

The anodic oxidation of 2,4,5-triarylimidazole was studied in aprotic solvents.291-295 The 2,4,5-triarylimidazole anions undergo a one-electron oxidation, forming dimeric bis-(2,4,5-triarylimidazolyls).294 The isomeric bis imidazolyls consist of imidazole and isoimidazole systems. The dimerization is a result of a nucleophilic attack of 2,4,5-triarylimidazole anions on the electrochemically generated 2,4,5-triarylimidazolium cations. 

Peroxodisnlfuryl difluoride reversibly dissociates into yellow flnorosnlfate radicals at elevated temperatures. In a I-l glass vessel, 100 Torr of S2O6F2 gives a bright yellow color when heated to 150 °C. The FSOs- radical is a powertul one-electron oxidant, forming the very stable fluorosulfate anion or covalent bonds with many metals and nonmetals (Scheme 7). 

It should be pointed out here that the geometries of molecular radical cations as primary one electron-oxidized forms and of their neutral precursors can be quite different, leading to high reorganization energies in the sense of the Marcus concept [5]. One of the better known examples in the field of main... 

For the Shilov system a mechanism was proposed which consists of three basic steps (1) activation of the alkane by a Pt" species, followed by (2) a two-electron oxidation forming a Pt intermediate and (3) reductive elimination of the oxidized alkane as shown in Scheme 4. 

Of these three metal compounds, thallium compounds such as T1(N03)3 and T1(0C0CF3)3 have been widely utilized in organic synthesis. Both TP+ and Pb" + ions are isoelectronic and the former is a less powerful oxidant than the Pb(IV) ion. Oxidizing reactivities of Tl+ salts vary with the anion associated with the metal, the solvent and other factors. On treatment with T1(N03)3 [TTN], phenols generally undergo two-electron oxidation forming phenoxonium ions which will be attacked by a variety of nucleophiles. 

An analog of the one-electron oxidized form has been isolated as [MoFe5(CO)6(S)6(I)3]2-, which, based on spectroscopic evidence, has been... 

Spectroscopic data support location of the radical in GAO on the Y272-C228 unit. The first indication came from UV-vis, EPR, and ENDOR studies of a one-electron oxidized form of Cu-depleted (apo) GAO, which showed the formation of a thioether-modified tyrosyl radical. " " This radical was found to be quite stable, as reflected by the oxidation potential of about-1-0.4 V (vs. normal hydrogen electrode (NHE)) which is significantly less than that of other tyrosine/ tyrosyl radical couples (cf.+0.93V for free tyrosine or +1.0V for the tyrosyl residue near the diiron site in ribonucleotide reductase, vide infra). Possible origins of this unusual stability that have been considered are the thioether substituent," the nearby W290, and/or other unspecified protein environmental effects. Coordination of this radical to Cu was then proposed for the... 

Computational studies of the geometry and electronic stmcture of an all-inorganic and homogeneous tetra-Ru-polyoxotungstate catalyst for water oxidation and its four subsequent one-electron oxidized forms. J Phys Chem A 114 535-542... 

Two and four electron oxidized forms of porphyrinogen, like those shown in the scheme or others, would have no chance of being trapped in the case of /we.yo-tetrahydrotetraalkylporphyrinogen, while they may be, eventually, identified in case of the /w o-octaalkyl form. 

The nickel has been shown by EXAFS to have a predominantly sulfur ligand environment. The epr active, odd-electron oxidized form, perhaps Ni(III), can be reduced to an epr inactive form, perhaps Ni(II), a more reduced, odd-electron form, perhaps Ni(I), accessible by H2 reduction, and an even more reduced even-electron form. The balance of probability is that the Ni(III) state may be formed as part of a mechanism for protecting the enzyme against exposure to air and that the catalytic cycle involves Ni(II) and more reduced states. Hydrogen activation by the enzyme is heterolytic because D2 exchanges with solvent protons, as shown here ... 

On the basis of these results, the one-electron oxidized form of complex 3 can be formulated... 

The reaction of Co3(dpa)4Cl2 with NOBF4 yields the one-electron oxidized form [Co3(dpa)4Cl2][BF4] (Scheme 13). The crystal structure of [C03 (dpa)4Cl2][BF4] shows that the Co-Co-Co unit is linear and essentially symmetrical. Two independent Co-Co distances are 2.3168 (8) and 2.3289 (8) A. The terminal Co-Cl and Co-N distances are shorter as compared to the neutral species. The factor contributing to a decrease in metal-ligand distances is the removal of one electron from the antibonding orbital of the neutral molecule. 

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