Halides redox properties

The above-discussed anionic ligands are the most important ones from the viewpoint of redox properties. For the sake of completeness, we can also consider the redox behavior of halides and boron. Halides stable in water are the simple... 

In addition to the acidic and basic properties mentioned previously, oxides and halides can possess redox properties. This is particularly true for solids containing transition metal ions because the interactions with probe molecules such as CO, H2, and O2 can lead to electron transfer from the surface to the adsorbed species and to the modification of the valence state of the metal centers. An important role in surface redox processes involving CO is played by the most reactive oxygen ions on the surface (e.g., those located at the most exposed positions such as corners), which can react with CO as follows ... 

Aminations of five-membered heterocyclic halides, such as furans and thiophenes, are limited. These substrates are particularly electron-rich. As a result, oxidative addition of the heteroaryl halide and reductive elimination of the amine are slower than for simple aryl halides (see Sections 4.7.1 and 4.7.3). In addition, the amine products can be air-sensitive and require special conditions for their isolation. Nevertheless, Watanabe has reported examples of successful couplings between diarylamines and bromothiophenes [126]. Triaryl-amines are important for materials applications because of their redox properties, and these particular triarylamines should be especially susceptible to electrochemical oxidation. Chart 1 shows the products formed from the amination of bromothiophenes and the associated yields. As can be seen, 3-bromothiophene reacted in higher yields than 2-bromothiophene, but the yields were more variable with substituted bromothiophenes. In some cases, acceptable yields for double additions to dibromothiophenes were achieved. These reactions all employed a third-generation catalyst (vide infra), containing a combination of Pd(OAc)2 and P(tBu)3. The yields for reactions of these substrates were much higher in the presence of this catalyst than they were in the presence of arylphosphine ligands. 

Couples such as hydroquinone/quinone have been hypothesized to dominate the redox properties of humic and fulvic acids, and to act either as electron transfer mediators or as the direct donors of electrons for dechlorination reactions (Schwarzenbach et al., 1990 Dunnivant et al., 1992). For example, it has been shown in sediment-water systems that the rates of alkyl halide reduction increase with organic matter content (Peijnenburg et al., 1992). Further support for this hypothesis was obtained by Svenson et al. (1989), who reported a first-order dependence between rates of hexachloroethane reduction and hydroxyl concentrations. Aside from alkyl halides, structural features of organic matter have been shown to catalyze (Fu et al., 1999) or accelerate (Barkovskii and Adriaens, 1998) the dechlorination of dioxins (Figure 9). 

An authoritative review on the chemistry of radon, which includes the formation of clathrate compounds, the simple and complex fluorides, ionic radon in solution, redox properties, and the various unsuccessful efforts to prepare an oxide and halides of radon other than the fluoride, was published by the most significant contributor to this field in 1983 (14). 

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