Aryls redox potentials

Much information can be gained by examining trends in redox potentials within series of compounds. Let us consider such a series of coordination compounds, M0, Mj, M2. .. M , which undergo reversible, one-electron oxidation reactions at potentials E°0, E°lf E°2,... E° respectively, with respect to the same reference electrode. If we define the oxidation of M0 as our standard reaction (equation 8), then we can examine the variation of the free energy difference, F(E°0— E° ), in terms of the structural difference between M0 and each other member M . Such an analysis is directly comparable to the classic approach of Hammett17 which relates a free energy difference term, log(AH/Ax), for equilibrium reactions such as (9) and (10), to the nature of the aryl substituent, X. 

Infrared vibrational energies of ligating groups such as CO, N2, NO or RNC (R = alkyl or aryl) have been extensively correlated with redox potential data.28 37""41 For a series of closely related mononuclear complexes it is generally observed that as E° (or EVl) for the oxidation of members of the series becomes increasingly positive, then v, the infrared stretching frequency for the (ter-... 

The electrochemical oxidation of 2,5-diaryl-1,4-dithiins (50) has been studied using various voltametric techniques and all compounds were found to undergo quasi-reversible one-electron transfers to the radical cations and dications.126 The first formal redox potential and the lifetime of the radical cation were found to decrease with increasing electron donation from the aryl ring. The major products were the 2,2 -dimers, which result via reaction of two radical cations for which rate constants are given. Dibenzothiophene radical cations reacted with tetranitromethane under... 

So the overall reaction (Equation 8.17) occurs at a redox potential close to that of the Nin/Ni° system, i.e. at -1.1 V/SCE, whereas Zn11 ions are reduced at ca. -1.4 V/SCE in DMF, and aryl halides are reduced at between -2 and -2.7 V/SCE. In addition, apart from N02, sensitive functional groups can be present on the ring, o-arylnickel compounds are reducibly converted into Ar-Ar (para- or meta-substituted compounds) or into Ar-H (ortho-substituted compounds). 

TABLE 12.1 Redox Potentials for Alkyl Halides (RX) and Aryl Chlorides (ArClx) in Dimethyl Formamide at a Glassy-Carbon Electrode"... 

One of the interesting features of these chiral viologens is that this kind of viologen can be systematically synthesized with a variety of bulky substituents. Their redox potentials moderately depend on the aryl substituent, and they are observed in the range of —0.17 to —0.24 V (E3+/2+ vs. SCE in water) [23]. 

The triarylaminium salts [N(aryl)3][X] in which the para position is substituted (in order to inhibit nucleophilic reactions at that position) are among the most useful oxidants because they are strong, almost innocent oxidants known for a range of standard redox potentials from 0.16 V to -1.76 V relative to FeCp2 depending of the nature and number of substituents (Table 10), and they are easily accessible by oxidation of the triarylamine in CH2CI2 using [NO] salts, silver salts in the presence... 

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