Pseudohalides

Lead(ii)Pseudohalides. The crystal structure of the complex Pb(SCN)2,Cj2H2j-N2O4 shows that the lead ion lies in the plane of the four oxygen atoms, the two nitrogen atoms being on both sides. The co-ordination sphere of the lead is completed by the sulphur atoms of the NCS ions, one above and one below the ring. The lead thus has hexagonal-bipyramidal co-ordination. The 

Pb—N and Pb—O bonds are essentially electrostatic, whereas the Pb—S bonds are covalent in character. The Pb—S, Pb—O, and Pb—bond distances are 2.894, 2.897, and 2.787 and 2.751 A, respectively. The effect of particle size on the thermal decomposition, the photodecomposition and electronic structure, and the i.r. spectra of adead azide have been studied. 

1 Carboxylates Among various 0-substituted electrophiles, O-acylated phenols share a few distinct advantages over other pseudohahdes (i) they are readily available and affordable, (ii) they are relatively stable substrates to various reaction conditions, and (iii) they can serve as directing groups for aromatic substitution reactions such as directed ortho-metallations (DoMs) [58]. Moreover, these carboxylates are much more environmentally friendly, generating acetate salts as the only by-product in the Suzuki-Miyaura cross-coupling reaction [59, 

This remarkable orthogonality allows sequential, chemoselective cross-coupling reactions to be orchestrated for the syntheses of a variety of triaryl products. 

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The other popular solution is to fill out the valence with atoms. Usually, H atoms are used as shown in Figure 23.1. Pseudohalide atoms have been used... 

Efficient homocoupling of the aryi iodonium salt 827 using Zn is catalyzed by Pd(acac)2[708], Homocoupling of the aryisuifonyl chloride 828 as a pseudohalide takes place in the presence of 2 equiv. of Ti tctraisopropoxide[7Q9]. 

In addition to the tri alkyl- and triaryldihaloarsoranes there are a number of compounds of the type R2ASY2, where Y is a pseudohalide, nitrate, carboxy, or other negative group. They are usually prepared from tri alkyl- or triaryldibromo- or dichloroarsoranes by metathesis. Thus dia2idotrimethyiarsorane [21121-84-6], C H AsN, has been prepared in the following manner (151) ... 

Chemistry of Halides, Pseudohalides and Azides, Parts 1 and 2, Patai S, ... 

Nucleophiles like alcohols [2, S], hydrogen sulfide [2], thiols [2,10], ammonia, amines, hydrazines, hydroxylamines [2 11, 12, 13, 14, 75], azides [2], other pseudohalides [2], phosphonates [2,16,17,18,19, 20], and phosphanes [2,19] add rapidly across the CO or CN double bond to yield stable adducts The phosphonate adduets undergo a subsequent aleohol—lester rearrangement [19, 20] (equation 2)... 

This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

Paralleling the various phosphorus trihalides are numerous pseudohalides and mixed pseudohalide-halides of which the various isocyanates and isothiocyanates are perhaps the best known. Most are volatile liquids, e.g. 

The corresponding phosphoryl and thiophos-phoryl pseudohalides are also known, i.e. P0(NC0)3, PS(NC0)3, etc. Preparations are by standard procedures such as those on the diagram for PCI3 (p. 497). As indicated there, P(CN)3 has also been made it is a highly reactive white crystalline solid mp 203° which reacts violently with water to give mainly phosphorous acid and HCN. 

Table 12.4 Some phosphoryl and thiophosphoryl halides and pseudohalides...

Oxohalides and pseudohalides Table 16.7 Some physical properties of selenium oxohalides... 

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... 

The name Sandmeyer reaction - is used for the replacement of the diazonium group in an arenediazonium compound by halide or pseudohalide, taking place in the presence of a metal salt. However this is not a strict definition, since the replacement of the diazonium group by iodide, which is possible without a metal catalyst, is also called a Sandmeyer reaction. 

Other RhX(CO)(PPh3)2 compounds can be made as shown in Figure 2.23 metathesis with an alkali metal halide or pseudohalide is often convenient, but the most versatile route, as with the iridium analogues, is a two-stage process in which the fluoro complex is first prepared, the fluorine then being readily displaced. 

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