Arylations hexafluorophosphate

Depending on structure, photolysis of films of arenediazonium fluoroborates and hexafluorophosphates at room temperature gives aryl fluorides m 10-75% yield [32] In situ photochemical decomposition of arenediazonium fluoroborates... 

Addition of hexafluorophosphate salts reduces the dediazoniation rate of 4-me-thylbenzenediazonium tetrafluoroborate in TFE/H20 (1 1) (Maskill and McCrud-den, 1992). However, as the concentration of these salts (0.12 — 0.23 M) does not affect the rate, it is evident that these salts are intercepting one of the intermediates, i.e., either the ion-molecule pair or the aryl cation. 

Ambroz and Kemp (1979 a, 1982 a, b) photolyzed benzenediazonium salts with donor substituents in the 4-position (2,5-di- -butoxy-4-morpholine-, 2,5-diethoxy-4-H-butylthio-, and 2,4,5-trimethoxy-benzenediazonium hexafluorophosphate in LiCl - H20 - acetone matrices at low temperatures, 77-130 K). Under these conditions the aryl cation formed is sufficiently stable to be identified spectroscopically. It is a triplet, a result that is consistent with earlier ab initio calculations by Dill et al. (1977), and with earlier observations by Lee et al. (1961), also at low temperature (77 K). 

Retrosynthetic analysis of the carbazomycins C (263) and D (264) based on the iron-mediated construction of the carbazole framework leads to tricarbonyl [3-methoxy-(l-5-ri)-cyclohexadienyl]iron hexafluorophosphate (779) and the aryl-amines 780a and 780b (see Scheme 5.84) as synthetic precursors (611). The arylamines 780a and 780b have been used previously as precursors for the total syntheses of carbazomycin A (260) and B (261) (see Schemes 5.86, 5.87 and 5.88). 

A special case for such aza[60]fuUerene arylation is the reaction of 2 with a 25-fold excess of ferrocenium hexafluorophosphate at 150 °C in an argon atmosphere, which afforded the ferrocenyl-hydroaza[60]fullerene dyad 31 (Scheme 12.10) [23]. 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

An intramolecular substitution of trimethylamine fix>m 17 gave a bicyclic oxetane 18 in a diastereoselective process <98MI2185>. A [2+2]cycloaddition of 2,2,4,5-tetrasubstituted 2,3-dihydrofuran to aryl aldehydes gave the bicyclic oxetane 19 <98JCS(P1)3261>. 2,2-Disubstituted-3-bromooxetane was obtained by a 4-endo-tcig cyclization process of 3,3 -disubstituted allyl alcohol in the presence of bis(collidine)bromine hexafluorophosphate <99JOC81>. 

Hexafluorophosphoric acid is a useful reagent for the conversion of arylamines into aryl fluorides 6 via decomposition of intermediate arenediazonium hexafluorophosphates 5 (see also Section 26.1.4.3.) and in some cases this procedure has a marked advantage over the use of fluoroboric acid (see Section 26.1.3.) in the same reaction.5... 

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). 

The use of ionic liquids in microwave chemistry has great potential and a number of research groups have introduced the use of ionic liquids in synthetic approaches43,44. l-Butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was recently evaluated as a solvent for the microwave-promoted Heck reaction45. Terminal arylations of electron-poor olefins were carried out rapidly with good-to-excellent yields, using the old-fashioned catalyst palladium chloride (Scheme 2.15). As an example, the... 

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... 

The conversion of aryl amines to aryl fluorides via diazotisation and subsequent thermal decomposition of the derived tetrafluoroborates or hexafluorophosphates. The decomposition may also be induced photochemically. 

Once the aryl cation is formed it reacts immediately with the best nucleophile in the reaction mixture. Being a very strong electrophile an aryl cation can even react with very weak nucleophiles. When the best nucleophile is H20—a weak one, indeed—a phenol is produced (Figure 5.41, left). Even when the nucleophile is a tetrafluorobo-rate or a hexafluorophosphate (which are extremely weak nucleophiles), SN1 reactions run their course, and an aryl fluoride is obtained. As the so-called Schiemann reaction, this transformation is carried out by heating the dried aryldiazonium tetrafluorobo-rates or hexafluorophosphates (Figure 5.41, right). 

Benzenetellurolate, generated by electrochemical reduction of diphenyl ditellurium in a solution of tetrabutylammonium hexafluorophosphate, reacted with electrochemically partly reduced chlorobenzonitriles5 and bromobenzophenones6 to produce aryl phenyl tellurium compounds in moderate yields. The following compounds were isolated from the reaction mixtures ... 

The caged species may escape geminate recombination and produce various species that can initiate cationic polymerization. Solvent (RH) often participates in these reactions producing protonic acids. As shown in Eq. (44), protonic acids are also formed by reaction of radical cations with aryl radicals or by Friedel-Crafts arylation. Up to 70% of the protonic acid is formed upon photolysis of diaryliodonium salts [205]. In addition to initiation by protons, arenium cations and haloarene radical cations can react directly with monomer. The efficiency of these salts as cationic initiators depends strongly on the counterions. Those with complex anions such as hexafluoroantimonate, hexafluorophosphate, and triflate are the most efficient. 

Addition of aryl azides to CpRh(PMe3)(CNMe) resnlts in conpling of the aryl nitrene with the isocyanide to form (110) (Ar = Ph, p-tol) which can be converted to (111) (R = H, Me), another example of a carbene complex (see also 73, Section 2.4, Carbene Complexes) Replacement of COD in Rh2(COD)2(/u-Cl)(/u.-PBu 2) by t-butylisocyanide yields Rh2(CNBu04(M-Cl)(/r-PBu 2), which on treatment with one equivalent of lithium di(t-butyl)phosphide forms [Rh(CNBu )2(/x-PBu 2)]2, which has a planar Rh2P2 core and no Rh-Rh bond. In a chloroform solution, the last complex is slowly converted into a mixture of cis- and frani -[RhCl(CNBuO(/tr-PBu 2)]2, while oxidation with ferricinium hexafluorophosphate yields [Rh(CNBu )2(/u.-PBu 2)]2 - Both of the oxidized dimers contain Rh-Rh bonds. ... 

---