Diazonium hexafluorophosphates, aryl

The diazonium hexafluorophosphates, prepared similarly from the appropriate diazonium chloride solution and hexafluorophosphoric acid, may in general be used instead of the fluoroborates with advantage. The thermal decomposition of diazonium hexafluorophosphates to aryl fluorides generally proceeds smoothly and in better yield.29... 

More prevalent than diazonium fluorosilicates in so-called modified Baiz-Schiemann reactions have been diazonium hexafluorophosphates.16 In some cases these latter diazonium salts give higher yields of aryl fluorides. Some examples are shown below, with the normal Balz-Schiemann reaction yields using diazonium tetrafluoroborates given in parentheses.163... 

Difluorotris(perfluoroalkyl)-25-phosphancs (Rf)3PF2 give stable salts with cesium fluoride, potassium fluoride, sodium fluoride or arenediazonium fluorides, i.e. Cat + [(RF)3PF3] , where Cal+ = Cs +. K+, Na +, ArN2+. The last are difficult to dissolve and they decompose at much lower temperatures (60-90 C) than tetrafluoroborates and hexafluorophosphates. which allows more complete precipitation of diazonium salts from water solutions and their conversion into aryl fluorides 6 without tar formation.6... 

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, tri aryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on triflic acid (158,163—166). Coordination polymerization of THF maybe in a different class (167). 

Fluorine can also be introduced onto aromatic rings via diazonium ions. One procedure is to isolate aryl diazonium tetrafluoroborates. These thermally decompose to give aryl fluorides presumably by formation of the aryl cation which abstracts fluoride from the anion.Hexafluorophosphate salts behave similarly.The... 

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