Preparation tetrahalides

Similar results are obtained for dre deposition of the carbides of these metals using methane as a source of carbon, atrd silicon tetrahalides for the preparation of silicides. These reactions are more complex than dre preparation of the diborides because of the number of carbides atrd silicides that the tratrsition metals form, some of which have wide ranges of non-stoichiometry. The control of the ratio of the partial pressures of dre ingoing gases is therefore important as a process variable. 

A halogenating system related to the preceding case is formed by the reaction of triphenylphosphine with molecular bromine or chlorine. The system is not as sensitive to moisture as the phosphine-carbon tetrahalide system (see preceding section), but it suffers from the disadvantage that hydrohalic acids are produced as the reaction proceeds. Nevertheless, sensitive compounds can be successfully halogenated by the system, as exemplified by the preparation of cinnamyl bromide from the alcohol. 

A highly explosive liquid [1]. Early attempts failed to isolate it but prepared numerous other explosive compounds. Reaction of dichlorine hexoxide with silicon tetrachloride or tetrabromide gave an explosive solid, apparently a perchlorato oligosiloxane. Silver perchlorate and silicon tetrahalides in ether gave explosive volatile organics, perhaps ethyl perchlorate. Replacing ether by acetonitrile as solvent, a solid (di)acetonitrile adduct of the tetraperchlorate precipitated, described as exceptionally explosive even in the smallest quantities [2],... 

Diboron tetrahalides, B2X4, are also known. These may be prepared in a variety of ways, among them the reaction of BC13 with mercury. 

Despite the large body of literature discussing the preparation and reaction chemis try of dichloromethylene in solution, very few reports of the isolation of the molecule have appeared. The technique of forming Group IV dihalides from the reduction of the tetrahalide with the metal has proved to be of great utility for production of SiX2 and GeX2, but has not been successful in the case of carbon. 

The advantages of the carbon tetrahalide-organophosphine-alcohol reaction to prepare halides are simplicity of experimental procedure good yields relatively mild, essentially neutral reaction conditions absence of allylic rearrangements. The reaction proceeds with inversion of configuration and is a useful simple device for converting optically active alcohols to chiral halides in high optical purity.12-22... 

The preparation and properties of numerous actinide haUdes have been described by D. Brown Although the oxidation numbers of actinides in halides can vary from II to VI, most solid state studies are limited to di-, tri- and tetrahalides. 

In this procedure cis- [dihalobis(2,4-pentanedionato)titanium(IV)] complexes (halo = F, Cl, Br) are prepared in high yields through the reaction of a titanium tetrahalide with 2,4-pentanedione in dichloromethane. 

Addition of hydrogen halides to alkynes preparation of alkyl dihalides and tetrahalides... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Zirconium(IV) and hafnium(IV) chlorides and bromides form 1 2 adducts of the type [ZrX4(RCN)2] (R = Me, Et, Pr or Ph X = Cl or Br) and [HfX4(MeCN)2] (X = Cl or Br).11SM24 These complexes may be prepared by (i) direct reaction of the metal tetrahalide with an excess of the nitrile120 123 or (ii) electrochemical oxidation of zirconium or hafnium metal in the presence of a solution of chlorine or bromine in acetonitrile.118 The adducts are moisture-sensitive, white solids, insoluble in nonpolar solvents, but soluble in acetonitrile. In the later solvent, [ZrBr4(MeCN)2 behaves as a nonelectrolyte.122... 

Zirconium and hafnium tetrahalides form six-, seven- and eight-coordinate adducts with polydentate phosphine and arsine ligands. The 1 1 adducts [MXt(dppe)] and [MX dpae)] (M = Zr, X = C1 or Br M = Hf, X = C1 dppe = Ph2PCH2CH2PPh2, dpae = Ph2AsCH2CH2AsPh2) have been prepared in benzene media. IR spectra of the [MCLt(dppe)] complexes exhibit four v(M—Cl) modes in the 353-278 cm-1 region, consistent with a six-coordinate octahedral structure.45... 

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