Halogens and pseudohalogens

The rate law for 1 reduction of copper(III) peptide complexes shown in equation (2) is consistent with a mechanism depicted in equations (3)-(5), 

The redox interactions of [Os(bipy)3] and [Os(bipy)3] with II and SCNl formed by pulse radiolysis have been studied and the reactions are likely to be outer-sphere in nature since no intermediate adducts were detected. This allows calculation of the one-electron reduction potentials for I2,12, and (SCN)J of 1.063, 0.172, and 1.331 V, respectively, at 22 C and 0.1 M ionic strength. 

Reduction of [AuCU] and [AuBr4] by F involves rapid attack by outer-sphere F on coordinated halide (2) to give IX , where X is Cl or 

Either a two-electron or a one-electron process with formation of Au(II) is involved. In the presence of excess [AuXi] , rapid interhalogen substitution reactions complicate the kinetic behavior. 

Initial substitution [equation (6)] is involved in the corresponding thiocyanate ion reduction. This is followed by an electron transfer step, 

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Addition of halogens and pseudohalogens to the cyclopropylthiocarbene chromium complexes 122 affords the 1,4-dihalo-1-phenylthio-l-alkenes 123 stereoselectively [65]. Electrophilic halogen is likely to activate the carbene complexes, followed by the homo-Michael addition of halide anion. (Scheme 44)... 

A number of different polar and nonpolar covalent bonds are capable of undergoing the oxidative addition to M( ). The widely known substrates are C—X (X = halogen and pseudohalogen). Most frequently observed is the oxidative addition of organic halides of sp2 carbons, and the rate of addition decreases in the order C—I > C—Br >> C—Cl >>> C—F. Alkenyl halides, aryl halides, pseudohalides, acyl halides and sulfonyl halides undergo oxidative addition (eq. 2.1). 

Parallels have been observed between the chemistry of the halogens and a number of other dimeric species. Dimeric molecules showing considerable similarity to the halogens are often called pseudohalogens. Some of the most important parallels in chemistry between the halogens and pseudohalogens include those illustrated for chlorine in Table 8-16. 

The halogen and pseudohalogen dimer radical anions, X2 (X = Cl, Br, I, SCN), react efficiently with phenols and phenolate ions to give the corresponding phenoxyl radicals (equation 6). 

Careful analysis of the products of the addition of halogens and pseudohalogens to glycals has led to a definitive picture of the factors yielding various stereochemistries and products (Figure 6.68), as follows. 

Amino-2,3-dihydro-l,4-benzothiazin-3-one (134) is a useful source of a wide variety of 6-substituted derivatives via diazotization. The amino group has been replaced by halogens and pseudohalogens, by NO, and by N02, as well as by HgCl, H2As03, and H2Sb03.61... 

The chlorine substituents of cyanuric chloride can be exchanged with other halogen and pseudohalogen substituents.96,133 140 2,4,6-Trifluoro-l,3,5-triazine (2) (see also p 683) is formed by the reaction of cyanuric chloride (1) with sodium fluoride.133... 

In contrast to the diverse chemistry of allylpalladium complexes, vinylpalladium intermediates have been involved mainly in the vinylpalladation of carbon-carbon unsaturated systems and in the insertion into carbon-hydrogen and heteroatom-hydrogen bonds (Scheme 10). It is found that a vinylpalladium species reacts with carbon electrophiles such as aldehydes, ketones, and nitriles (Scheme 11, type a). Oxidative addition of vinyl-halogen and -pseudohalogen bonds to Pd(0) is the common way to generate the vinylpalladium species. Vinyl-... 

Olefins are essentially soft donors, tt Complexation of alkenes with soft metal ions, such as Ag , Pt , and Pd , is well established. The addition of halogens and pseudohalogens is commonly regarded as proceeding via the n complexes, as detected spectroscopically for the olefin-bromine charge-transfer species (24). 

Major applications of ion pair extraction are alkylations (mainly C-alkylations), synthesis of esters, halogen and pseudohalogen exchanges, oxidations and reductions . In these cases, it is obviously important to recover and recycle the quaternary salt. A number of methods to this end were proposed by Brandstrom. ... 

The reactions of pentafluorothio olefins are broad, with cycloadditions being rare l-SF5-l,3-cyclohexadiene can be dehydrogenated to QH5SF5 (20). Additions of halogens and pseudohalogens take place easily nucleophilic and electrophilic additions or nucleophilic substitutions may occur (20,21). 

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