Aryl -, onium halide

The coordinatively unsaturated aryl tellurium halides, when refluxed with an onium halide in an organic solvent, accept a halide ion to form salts of aryldihalotellurates(II)3 4 (p. 298). 

Onium Aryltetrahalotelluratcs(IV) [Organic Medium]1 3 mmol of the aryl tellurium tri halide are dissolved in dry methanol or ethanol, a solution of 3 mmol of the onium halide in the same alcohol is added dropwise at 20°, and the precipitated product is filtered yield > 85%. 

Onium Aryltetrahalotelliirates(TV) [Aqueous Medium]2 1 mmol of the aryl tellurium trichloride (or tribromide) is dissolved in 6 molar hydrochloric acid (or 3 molar hydrobromic acid) and a solution of 1 mmol of the onium halide in 20 ml of water is added dropwise with stirring. The product precipitates immediately yield 100%... 

Halogen exchange reactions may be used to prepare tetrahalotellurates(IV) that are not accessible through reactions of aryl tellurium trihalides and onium halides. Treatment of tetrachloro- or bromotrichlorotellurates with dilute hydrobromic acid produces the tetrabromotellurates. The conversion of bromotellurates to tetrachlorotellurates requires concentrated hydrochloric acid. Chlorine and bromine are easily replaced by iodine when the tellurates are reacted with excess potassium iodide in dilute hydrochloric acid. The iodotellurates cannot be converted to the bromo- or chlorotellurates ... 

In the reaction of activated aryl halides with phenoxide and thiophenoxide in chloro- or o-dichloro-benzene at reflux, pyridinium salts (48 R, R = —-CH2CH2CHMeCH2CH2— R = Me, Bu", n-C6Hi3 R = CH2CHEtBu, CH2BU1) proved to be superior catalysts to simpler onium salts, like TBAB, due mainly to their greater thermal stability.162... 

Halide displacement by thioanions such as thioalkoxides, thiocyanate and sulfite, can be readily carried out under PTC conditions in activated arenes. The reaction of nitro- and dinitro-aryl halides with thiophenol and NaOH in the presence of an ammonium or phosphonium salt catalyst proceeds readily in toluene at room temperature to give the phenyl aryl sulfides in nearly quantitative yield.189 Excellent yields of thiocyanoarenes were obtained from the reaction of the 2,4-dinitrohalobenzenes with KSCN in toluene at 90 C with a tetraalkyl onium salt PTC catalyst.190... 

Mixed tetrahalotellurates(IV) result from the combination of an aryl tellurium trihalide with an onium salt containing a halide different from that in the tellurium compound. 

Suzuki-Miyaura coupling, involving the reaction of aryl boronic derivatives with aryl halides in the presence of a palladium catalyst, is a very powerful method for the preparation of biaryls. Solutions of aryl bromides or iodides supported on onium salts via an ester link in an RTIL lead to BTSILs that can be engaged in the Suzuki-Miyaura coupling reaction with aryl boronic derivatives. like the Heck reaction, this coupling is also sensitive to the variations in different parameters. The possibility to synthesize libraries of biarylic derivatives by parallel synthesis is illustrated by (Scheme 5.5-39) [51]. 

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