Simple Halides

As already noted, the simple salts in this oxidation state are powerful oxidising agents and oxidise water. Since, also, Co(III) would oxidise any halide except fluoride to halogen, the only simple halide salt is C0F3. Cobalt(lll) Jluoride, obtained by reaction of fluorine with cobalt(II) fluoride it is a useful fluorinating agent. 

In addition to simple halides, the method was used to prepare chol-esteryl iodide (30%) and cyclohexyl iodide (34%) from the corresponding alcohols, thus demonstrating the applicability of the reaction to cyclic secondary alcohols. An early adaptation to carbohydrates was reported by Lee and El Sawi (75). They claimed that treatment of l,2 5,6-di-0-isopropylidene-D-glucofuranose (49) with triphenylphosphite methiodide... 

The halogens are reactive even without water. All the halogens react quite vigorously with most of the metals to produce simple halide salts. Copper and nickel, however, appear to be quite inert to F2. This apparent inertness is attributed to the fact that a thin layer of the fluoride salt forms on the surface of each of those metals and protects it from further attack by fluorine. 

Unfortunately, the requirements cannot be fulfilled by a single salt, because they are partially contradicting. For example, the last two requirements would be best fulfilled with simple halides such as LiF or LiCl. However, their solubility in every suitable solvent is low, due to their high lattice energies. In addition, these salts show strong ion-ion interaction forces, even in solvents of high permittivity. 

The (EDT-TTF-I)2Br salt described above [36] and the 1 1 (TTFI4)I salt reported by Gompper [51] were the only structurally characterized salts with simple halide anions until Imakubo recently described an extensive series of Cl" and Br" salts from several ortho-diiodo tetrathiafulvalene, tetraselena-fulvalene and dithiadiselenafulvalene derivatives (Scheme 8) [62], The X-ray crystal structure analysis of the nine salts described there show a variety of halogen bonded motifs, demonstrating the adaptability of the supramolecu-lar interactions to other structural requirements imposed by the nature of the heteroatoms (O, S, Se) in the TTF frame. Indeed, in (EDT-TTF-l2)2X-(H20)2 (X = Cl, Br), a bimolecular motif (Fig. 6) associates two partially oxidized EDT-TTF-I2 molecules with one Br" anion and one water molecule. 

A variety of leaving groups (other than simple halide) may be associated with the electrophilic component of the reaction with these phosphorus components. These include haloepoxides (leading to (3-ketophosphoryl compounds),59 quaternary ammonium salts,60-64... 

In 1884, Sandmeyer, however, made the important discovery that in the presence of the corresponding cuprous salt chlorine and bromine are also directed to the nucleus. This catalytic action has not yet been explained. Perhaps a double salt is formed, or else a complex salt in which the halogen is more firmly bound than in the simple halide. According to Gattermann, the cuprous salt may be replaced by copper powder. In general, the decomposition of labile diazo-compounds, by elimination of elementary nitrogen, is accelerated by copper. 

Square-planar complexes of platinum(II) and palladium(II) have been known for a long time the comparatively simple unit cells of compounds such as K2PdCl4, K2PtCl4, and Pd(NH3)4Cl2H20 led to early elucidation of the structures (257) and they all contain square-planar ions. The simple halides PdCl2 and Pt,Cl2 (71) consist of chains in which the metal is bonded from the corners of a square. Nickel chloride, on the other hand, has a layer lattice in which the nickel is octahedrally coordinated, and in the halide complexes the coordination is tetrahedral, as described in Section IV,B. 

It is suggested that substances such as potassium cliloraurate are dissociated first by ammonia into simple halides, for the alkali clilor-aurates and bromaurates behave towards ammonia like the auric salts.2 Auric bromide, obtained by dissolving precipitated gold in bromine, also absorbs ammonia, the amount depending on the temperature. 

This chapter has been devoted to the coordination chemistry of titanium and has made no attempt to describe the more basic chemistry of this element. References to alloys, to the simple halides and oxyhalides, the oxides, sulfides, selenides, tellurides, nitrides, azides, phosphides, arsenides and antimonides are well reviewed by Clark,14 and the recent text by Greenwood and Earnshaw180 contains a good section on titanium. 

In addition to the simple halides, boron forms fluorine complexes containing the fluoroboratc ion (BF4 ) Subhalidcs of boron arc known (B2X4) of the structure ... 

Because of the reactivity of lithium with water lo lomi its hydroxide. LiOH. and hydrogen, its properties when dissolved in other solvents have been studied extensively. It dries not decompose liquid H<. hut does form a blue solution, which decomposes to yield its amide, LIN IT. and hydrogen, when catalyzed by metallic salts. With the elements of main groups 2 to 7. lithium in liquid NIL, reacts lo form binaty compounds, which may vary from simple halides, as with the halogens, to inlermetallic phases, as with cadmium and mercury. Lithium amide in liquid NIL is regarded in the same class as a hydroxide ill aqueous solution. 

Ilia Simple halides halite NaCl, fluorite CaF2, chlorargyrite AgCl... 

Interestingly, for these compounds simple halide ions constitute the counter anion in salt formation. The compactness of the ring, especially in the case of L3, does impose a severe steric constriction at the metal centre. In the case of uncomplexed L2 the preferred endodentate conformation identifies it as an (almost) ideal ligand for occupation of three metal coordination sites (fac-octahedral)16-20. For free L3 there are four chair conformers... 

Iodonium salts readily transfer one of their aryl groups to a heteroatom substrates successfully arylated range from simple halide anions to complex natural products. The plethora of such reactions leaves no doubt that the use of iodonium salts is the best choice for arylations. 

A number of nitrido manganese complexes have been reported. Most of these complexes are Mnv, with only one example reported for Mnvn. These complexes typically incorporate polydentate ligands thus, no examples could be found of simple halide or alkoxide nitrido manganese complexes. Since the original disclosure by Groves and co-workers that these could be utilized as nitrogen transfer reagents, they have received considerable attention [48,49]. ... 

All these elements do not occur free in nature and are always found in combination with metals, generally as the simple halides. The tendency to form anion, X-, is weakest in astatine and is weak in iodine. 

Simple halides normally undergo direct electrochemical coupling in very low yields819. However, use of nickel complexes as catalysts has been used to synthetic advantage820. Also, the use of a sacrificial anode has much improved the procedure for electrochemical coupling and this process has been reviewed recently821. 

Upon treatment of the filtrate from 1 with sodium nitrite solution, chlorate and bromate are reduced to the simple halides, the presence of which is revealed by the separation of silver chloride and silver bromide respectively. Chromates (which, of course, yield a coloured solution) are simultaneously reduced to chromium(III) salts. 

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