Of halogens and pseudohalogens

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)... 

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. 

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). 

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). 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

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. 

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-... 

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. ... 

Pseudohalides of Se in which the role of halogen is played by cyanide, thiocyanate or selenocyanate are known and, in the case of Se are much more stable with respect to disproportionation than are the halides themselves. Examples are Se(CN)2, Se2(CN)2, Se(SeCN)2, Se(SCN)2, Se2(SCN)2. The selenocyanate ion SeCN is ambidentate like the thiocyanate ion, etc., p. 325), being capable of ligating to metal centres via either N or Se, as in the osmium(IV) complexes [OsCl5(NCSe)], [OsCl5(SeCN)], and trans-[OsCU(NCSe)(SeCN)]2-.920) Tellurium and polonium pseudohalogen analogues include Te(CN)2 and Po(CN)4 but have been much... 

Dimethyltin dichloride has a similar chain structure (375). In diethyltin diiodide (374), dimethyltin diisothiocyanate (376, 377), and di-chloro bis(chloromethyl)stannane (378), however, the distorted, trans-RgSnX geometry of each tin atom is completed by two bridging bonds involving the halogen or pseudohalogen atoms on the same, neighboring molecule. 

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