Partially Substituted Halides

Linear phosphazenes with terminal NH2 groups react with halogeno-phosphoranes to give phos- 

Mixed chlorobromo phosphazenes P3N3Clg Br can be prepared directly from an appropriate mixtnre of phosphorus and ammonium halides, heated in tetrachloroethane at llO C (7.352). A mixture of PBrj, Br2 and NH4Br give P3N3Cl4Br2. Various fluorochloro compounds are known. 

Phenyl-substituted derivatives can be prepared by Friedel-Crafts-type reactions (7.353) (cf. 7.333), or by reactions such as (7.354) and (7.355). 

Although the parent hydrides (PNH2) have not yet been prepared, derivatives with a limited number of H atoms are known, for example. 

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Partial substitution of halides on bismuth predictably gives alkoxy-bismuth halides, and salts of bismuth anions are obtained by reaction of the alkoxide with an ammonium or phosphonium halide (28). Two isostructural derivatives [Bi2Cl4(thf)2(ju,-OAr)2] (Ar = C6H3Me2-2,6 and C6H2Me3-2,4,6) are composed of dimeric units residing on a C2 axis 8. The bismuth is in a five-coordinate distorted square pyramidal geometry in each case. The apical sites are occupied by terminal... 

Because of their increased acidity, it is possible for phenols to effect total substitution of halide ligands in cases where alcohols cause only partial substitution. Hence, although WC16 reacts with ethanol to give the Wv complex [WCl3(OEt)2]2,35 phenol in benzene gives W(OPh)6 in excellent yields.4,36 Similarly, the phenoxides of Ti,37 Nb and Ta38 have been obtained. In cases where only partial replacement by phenol occurs, the use of substituents that increase the phenolic acidity can sometimes aid the reaction, for example as shown in equation (7).39,4(1... 

VO(OR)3 are very convenient and easily available precursors for the preparation of a wide range of V(V) derivatives and via their reduction by matalla-lkyls even for the derivatives of the lower oxidation states. The complete or partial substitution of OR-groups has led to halides, carboxylales, P-diketo-nates, alkyls, sulfides, azids, complexes with Shiffbases, phenylisocyanate, and so on. Hydrolysis of VO(OR)3 is discussed in Chapter 9. 

Ge tetraalkoxides can be produced through the complete alcoholysis of Ge halides in the presence of a base. Partial substitution yields many Ge alkoxy derivatives (alkyl orthogermanates) (equations 27 and 28). 

The Wurtz reaction as a method of alkylating germanium tetrachloride has never achieved the popularity of the Grignard reaction, chiefly because the difficulty of control makes it reasonably successful only as a means of preparing the fully substituted tetraalkyls or tetraaryls. The partially substituted germanium halides appear only in low yields since the reaction as usually conducted goes to complete substitution. One explanation is based upon the heterogeneity of the system. The sodium is unavoidably... 

The precise shape of the M4 core can be varied by partial substitution of OR with halide, and ranges from square to butterfly but apparently never tetrahedral ... 

Cationic Compiexes. Apart from the aqua ions and partially substituted species such as [GaCl(H20)5] +, cationic complexes of gallium halides with pyridine, bipyridine, or phenanthroline are known, for example, [GaCl2(phen)2]+ and [Ga(phen)3] +. Furthermore, given the steric hindrance about the gallium center in complexes formulated as GaX3(NH3) (X = Cl, n = 1, 3, 5, 6, 7, 14 X = Br, n = 1, 5, 7, 9, 14 X = I, n = 1, 5, 6, 7, 9, 13, 20), it is likely that where n is greater than 3 these are also cationic solvates. 

The simple alkyl and aryl-thio phosphorus derivatives, (RS)gP, (RS)aPO and (RS)gPS, can readily be prepared from phosphorus trichloride (or phosphorus pentachloride), phosphoryl chloride or thiophosphoryl chloride, and the corresponding lead thiolate Partially substituted compounds, such as ClxP(SCFa)3 j, are sometimes formed . Substituted derivatives R2P(SRi) and RP(SR )2 can be prepared from the corresponding halide and lead thiolate - " . Various mixed fluorophosphoranes, such as MePF2(SEt)2, can be prepared from MePF4 and ethanethiol or its sodium salt . 

By selective esterification with sulphonyl halides partially substituted sulphonate esters of sucrose can be prepared. For example, using limited quantities of toluene- -sulphonyl ( tosyl ) chloride in pyridine and subsequent purification by column chromatography, the 6,6 -ditosylate (G), 1 6,6 -tritosylate (H), and 1, ... 

Alkoxides are readily formed from partially substituted polyols and sugars by treatment with sodium naphthalenide 19) in 1,2-dimethoxy-ethane solution and subsequent reaction with alkyl halides then produces ethers 20). The reaction sequence is simple to apply, and the method deserves further investigation. 

Halide substitution on the anion site in LiBHi, i.e., partial substitution of (BHt) for F , Q, Br , or r, has been found to influence the phase transition temperature [64]. Here, in contrast to the alkali substitution presented in the previous section, iodide is systematically substituted into the anion sites in different concentrations. Figure 18.7 shows the energy of LiBHt s high temperature structure (P63mr) relative to the low temperature structure (Pnma) as function of the iodide concentration. The stabihty of the high temperature structure is graduaUy increased relative to the low temperature structure as we move toward higher iodide concentrations [65]. 

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