II Halides

In recent years, more novel methods have been developed by chemists in order to hasten the reaction between solids or to grow single crystals of new and exotic solids. Among those included in the following syntheses are electrolysis of fused salts, chemical transport, and hydrothermal crystal growth. 

Iron(II) chloride and bromide may be obtained from the reaction of the metal with the appropriate hydrogen halide at elevated temperatures.1 The chloride has also been made by the reduction of iron(III) chloride with hydrogen,1 from iron(III) chloride and the metal in tetrahydrofuran,2 and by the reaction of iron(III) chloride with chlorobenzene.3 The iodide has been prepared from the metal and iodine in a sealed tube at elevated temperatures.1 

The simplest procedure, dissolution of metallic iron in the aqueous mineral acid, suffers from the risk of accidental oxidation. The following relatively simple procedure overcomes this difficulty. This method, with minor modifications, has also been used successfully by the author for the preparation of chromium-(II) halides. 

Acid Approx. strength, % Amount, cc. Approx, yield of FeX, 6- X.%  

The amounts of mineral acid recommended for 10 g. of iron powder, the approximate yield of product, and halogen analyses are shown in Table I. 

Submitted by PIERO NANNELU and B. P. BLOCK Cheeked by D. A. EDWARDSt and A. K. MALLOCK  

Molybdenum(II) halides, which can be formulated (Mo X8)X4 (X=C1, Br, or I), are typical metal-cluster compounds. The 

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Other Group II halides are essentially ionic and therefore have relatively high m.p., the melts acting as conductors, and they are soluble in water but not in organic solvents. 

Cobalt is a bluish silvery metal, exhibits ferromagnetism, and can exist in more than one crystal form it is used in alloys for special purposes. Chemically it is somewhat similar to iron when heated in air it gives the oxides C03O4 and CoO, but it is less readily attacked by dilute acids. With halogens, the cobalt(II) halides are formed, except that with fluorine the (III) fluoride, C0F3, is obtained. 

Cobalt II) halides can be obtained by direct combination of the elements, or by dehydration of their hydrates. Anhydrous cobalt(II) chloride is blue, and the solid contains octahedrally-coordinated cobalt the hydrated salt C0CI2. bHjO is pink, with each cobalt surrounded by four water molecules and two chloride ions in a distorted octahedron. 

Alkyl- and arylmercury(II) halides are used for the ketone formation[402]. When active methylene compounds. such as /f-keto esters or malonates are used instead of alcohols, acylated / -keto esters and malonates 546 are produced, For this reaction, dppf is a good ligand[403]. The intramolecular version of the reaction proceeds by trapping the acylpalladium intermediate with eno-late to give five- and six-membered rings smoothly. Formation of 547 by intramolecular trapping with malonate is an example[404]. 

Perfluoroalkyltin halides can be prepared via oxidative addition of perfluo-roalkyl iodides to tin(II) halides in dimethylformamide (DMF) [12] The per-fluoroalkyltin(IV) dihalide could not be isolated, but in DMF solution, the tin(lV) compound did react with aldehydes and ketones in the presence of pyndine [12] (equation 8) Typical perfluoroalkylcarbinols prepared by this method are shown in Table 1 [12]... 

II. Halides from Alcohols and Phenols by Triphenylphosphine Dihalide... 

The other palladium(II) halides are all diamagnetic. PdCl2 exists in well defined a- and /3-forms [16] (as well as a 7-form) the former has a PdCU/2... 

In contrast to the situation with copper-based catalysis, most studies on ruthenium-based catalysts have made use of preformed metal complexes. The first reports of ruthenium-mediated polymerization by Sawamoto and coworkers appeared in I995.26 In the early work, the square pyramidal ruthenium (II) halide 146 was used in combination with a cocatalyst (usually aluminum isopropoxide). 

Preparation, structures and properties of vanadium(II) halides and complex halides. C. Cros, Rev. Inorg. Chem., 1979, 1,165-204 (93). 

The possible mechanism for the reactions involving stoichiometric amount of preformed Ni(0) complexes is shown in Fig. 9.8. The first step of the mechanism involves the oxidative addition of aryl halides to Ni(0) to form aryl Ni(II) halides. Disproportion of two aryl Ni(II) species leads to a diaryl Ni(II) species and a Ni(II) halide. This diaryl Ni(II) species undergoes rapid reductive elimination to form the biaryl product. The generated Ni(0) species can reenter the catalytic cycle. 

Table 9-2. log values for zinc(ii) and mercury(ii) halide complexes. 

Table 9-3. log Ki values for iron(iii) and lead(ii) halide complexes. 

Alkoxybenzenes were highly regioselectively halogenated by use of copper(II) halides supported on alumina to give 4-halo-alkoxybenzenes in high yield. Bromination of alkoxybenzenes with alumina-supported copper(II) bromide occurred at lower temperature than chlorination with alumina-supported copper(II) chloride (ref. 14). 

The yield increased with increasing the ratio of alumina-supported copper(II) bromide to alkoxybenzenes. The size of alkoxy group did not influence significantly the yield and the ratio of p/o. Nonpolar solvents such as benzene and hexane were better than polar solvent. Polar solvents such as chloroform and tetrahydrofiiran decreased the yield. It is suggested that these polar solvents may be strongly adsorbed on the surface of the reagent. The reaction did not proceed in ethanol to be due to the elution of copper(II) bromide from the alumina to the solution. It is known that the reaction of aromatic hydrocarbons with copper(II) halides in nonpolar solvents proceeds between aromatic hydrocarbons and solid copper(II) halides and not between hydrocarbons and dissolved copper(II) halides (ref. 6). 

Attempts to prepare In(II) halide complexes by this method are unsuccessful. Anodic oxidation of In metal produces In which disproportionates to the clement and In(II) halide complexes- . 

Similarly, Hg(II) halides yield compounds containing two transition-metal-Hg bonds ... 

Good yields of chlorides have also been obtained for reaction of isolated diazonium tetrafluoroborates with FeCl2-FeCl3 mixtures.100 It is also possible to convert anilines to aryl halides by generating the diazonium ion in situ. Reaction of anilines with alkyl nitrites and Cu(II) halides in acetonitrile gives good yields of aryl chlorides and bromides.101... 

In a thorough work with an extensive literature survey, crystal structures, vibrational and 31P NMR spectra of several phosphine complexes of mercury(II) halides HgX2 are presented.235 In the dibenzophosphole complex (dbp)2HgBr2, Hg adopts a distorted tetrahedral coordination (rav(Hg—P) 250.2, rav(Hg—Br) 261.1pm) (cf. the related Cd complex in the previous paragraph), with slightly shorter Hg—P and Hg—Br bonds, respectively, than in the comparable... 

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