Tetrafluoroborate salts

Hexafluorophosphate and tetrafluoroborate dienyl salts react with many nucleophiles. The tetrafluoroborate salts are to be preferred, being more soluble in organic solvents than the hexafluorophosphates. 

Attempts to prepare 2-aminoazepinium cations by the action of trityl tetrafluoroborate on 3//-azepin-2-amines have failed,64 as have attempts to Ar-methylate 2,5,7-trimethyl-3/f-azepine with an excess of iodomcthanc in a scaled tube at 100°C for seven hours.77 In contrast, the unstable Ar,Ar-dialkyl-6-(methylsulfanyl)-3//-azepin-2-amines, e. g. 1, with trityl tetrafluoroborate, or the corresponding nitrosonium salts, yield their tetrafluoroborate salts, e.g. 2s4 (see also Section 3.1.1.5.4.). 

Methyl-5-oxo-l-phenyl-4,5-dihydropyrazol-4-ylidene)-2,3-dihydro-l//-azepine (3), formed in 62% yield by the condensation of 2-amino- or 2-butoxy-37/-azepine with 3-methyl-l-phenylpyrazol-5(4//)-one, with Meerwein s reagent yields the tetrafluoroborate salt 4 which, on treatment with sodium dihydrogen phosphate, liberates the free base 5.64... 

The Balz-Schiemann reaction continues to attract attention, with much of it generated by the interest in fluoroquinolones, e.g., (7), which is a potential antibacterial. Two approaches to its synthesis are possible—introduction of fluorine prior to or post ring construction. Decomposition of the tetrafluoroborate salt was unsuccessful, whereas the PF6 salt (8) gave only a poor yield (84JMC292). A more successful approach was the introduction of F into the pyridine nucleus prior to formation of the 1,8-naphthyridine ring (84JHC673). A comparison of decomposition media showed that cyclohexane was the best with regard to yield and time. 

The Stability of hydrocarbon ions is discovered intuitively by observing whether the hydrocarbon ion can be isolated as a salt, for example, a sodium salt of the carbanion or a tetrafluoroborate salt of the carbocation. Conversely, a single hydrocarbon ion produced in the gas phase is obviously an unstable and short-lived species. Thus, many of the aliphatic carbocations in the gas phase are merely observable species but are not usable for synthesis. 

Boron trihalides are strong Lewis acids that react with a wide collection of Lewis bases. Many adducts form with donor atoms from Group 15 (N, P, As) or Group 16 (O, S). Metal fluorides transfer F ion to BF3 to give tetrafluoroborate salts LiF + BF3 LiBF4 Tetrafluoroborate anion is an important derivative of BF3 because it is nonreactive. With four <7 bonds, [BF4 ] anion has no tendency to coordinate further ligands. Tetrafluoroborate salts are used in synthesis when a bulky inert anion is necessary. 

Salts containing the nitronium ion can be prepared and are reactive nitrating agents. The tetrafluoroborate salt has been used most frequently,8 but the... 

In the classical procedure, base is added to a two-phase mixture of the aqueous diazonium salt and an excess of the aromatic that is to be substituted. Improved yields can be obtained by using polyethers or phase transfer catalysts with solid aryl diazonium tetrafluoroborate salts in an excess of the aromatic reactant.177 Another source of aryl radicals is A-nitrosoacetanilides, which rearrange to diazonium acetates and give rise to aryl radicals via diazo oxides.178... 

Aromatic diazo compounds can be reduced in water via a radical process (Scheme 11.5).108 The reduction mechanism of arenediazo-nium salts by hydroquinone was studied in detail.109 Arenediazonium tetrafluoroborate salts undergo facile electron-transfer reactions with hydroquinone in aqueous phosphate-buffered solution containing the hydrogen donor solvent acetonitrile. Reaction rates are first order in a... 

To further demonstrate the stability and unreactivity of the isopropenylferrocene carbenium ion, a stable derivative of this ion was prepared and evaluated as an initiator for the cationic polymerization of styrene. The derivative prepared for this purpose was the tetrafluoroborate salt of the isopropenylferrocene carbenium ion. Even at 20°C a 26% yield (Mjj = 11,315, = 18,815) of... 

They have been prepared with several anions,332-335 the tetrafluoroborate salt exhibits SA and Sc phases332,333 but the triflate shows a nematic phase 334 One of the problems in studying these complexes was the very high temperatures at which the phases existed and the fact that decomposition was often observed in the upper reaches of the SA phases. Reduction of these temperatures was achieved by changing the small anions for dodecyl sulfate that also make that more materials exhibit nematic SA and Sc phases, and another more viscous phase appeared, named cubic phase So- With the anion octyl sulfate336 the crystal structure of one of the complex with 4-metoxystilbazole could be achieved (20), with this anion the cubic phase was not present. 

The intermolecular cyclization that involves the peri positions of unsubstituted systems (6 6) has been applied to the construction of fused (6 6 6) systems. An example of this approach is the reaction of bicyclic guanidine 123 with 1,3-dibromopropane furnishing the /wi-fused product 124 which can be isolated as tetrafluoroborate salt (Equation 12) C1996CB21, 1997TL1911>. 

X-ray structural analysis of the methylsulfate compound indicates the orthorhombic crystal unit cell contains two translationally inequivalent cations positioned on mirror planes and tilted at 3 ° relative to the two-fold screw (c) axis (23). This is a compromise orientation for simultaneously, rather than individually, maximizing x ccc and x /> bbc in this polar structure. This structure is therefore consistent with the extremely large SHG intensity reported in Table 1 while, also consistently, preliminary x-ray data show the perrhenate and tetrafluoroborate salts to be isostructural (23.). Details of the packing... 

CAS 1714-38-1 69044-01-5 (Fluorosulfate salt) 25059-10-3 (Perchlorate salt) 25482-84-2 (Perchlorate salt) 54098-95-2 (Perchlorate salt) 29630-03-3 (Tetrafluoroborate salt)... 

In 1977 Driessen and van der Voort identified an extremely abrupt spin crossover with Tm of 213 K for [Fe(isoxazole)6](Cl04)2 [71]. Although various spectroscopic techniques have been employed to study this spin transition, the structural features of this compound at the time could not be determined, due to its extreme sensitivity to decomposition [71]. The same applies to the tetrafluoroborate salt that also displays a spin crossover, but in this instance a two-step transition was observed [71]. 

Recently, this family of isoxazole compounds has been re-examined with particular emphasis on the tetrafluoroborate salt. These studies included the first extended magnetic and structural characterisation of [Fe(isoxa-zole)6](BF4)2 [72]. In addition, the double salt [Fe(isoxazole)6] [Fe(isoxa-zole)4(H20)2](BF4)4 was isolated [73]. 

Some 4,5-dihydro[l,2,4]triazolo[3,4-r-]benzo[l,2,4]triazines 57 easily reacted with aromatic aldehydes to result in the formation of synthetically valuable azomethine imines 58 <2005EJO3553>. The transformation took place at room temperature in the presence of tetrafluoroboric acid in 10 min in high yields. The product 58 was conveniently prepared and stored in the form of tetrafluoroborate salt, and was subjected to further reactions (e.g., 1,3-dipolar cycoadditions see Section 11.19.5.4.) by in situ liberation of the free base prior to transformation. 

The synthesis of ionic liquids with BF4 and PF6 as cations has been the subject of much research since they are the most widely used in catalysis. However, it is difficult to make these ionic liquids in a pure form. The original route used to prepare ionic liquids with these anions consists of a metathesis (anion-cation exchange) reaction in which the imidazolium chloride is reacted with the sodium salt of the anion in a suitable solvent [8], The reaction is illustrated in Scheme 4.2 for the tetrafluoroborate salt. 

Several substituted title salts, intermediates in the preparation of 1,3-diselenole-2-selenones, exploded on heating, ignition or shock. The tetrafluoroborate salts were stable, safe intermediates for large-scale application. Individually indexed compounds are ... 

Common precursors for the enantioselective hydrogenation with the use of cationic rhodium are the tetrafluoroborate salts of bis-alkadiene rhodium. As a solvent one often uses dichloromethane or methanol, in which tetrafluoroborate is indeed weakly or non-coordinating. The first alkadiene at rhodium is rapidly replaced in situ by the phosphorus ligands added. 

Diazonium salts are another useful source of free radicals, and the formation of the reactive species can be achieved by reductive electrolysis or direct treatment with diazonium tetrafluoroborate salts [39]. By this route, several aryl derivatives could be introduced onto the nanotube sidewalls [40]. Aryl groups bearing halogen or alkyne functionalities are particularly interesting as they can be further reacted in Pd-catalyzed coupling reactions (Suzuki, Heck) or in click chemistry reactions to create products with great potential in materials science [41]. 

There has been significantly less exploration of the corresponding ditellur-oethers. However, by analogy to diselenoether 112, 1,5-ditelluracyclooctane 118 was prepared, and converted to ditelluradication tetrafluoroborate salt 118a (Fig. 41) as well as to the hexafluorophosphate salt. " As expected, 118 was oxidized reversibly even more readily than 112 = —0.02 V) (Table 15) and... 

These changes in anion and cation were not merely a case of methyl, ethyl, propyl, butyl, and then futile. The change of anion dramatically affects the chemical behavior and stability of the ionic liquid the change of cation has a profound effect on the physical properties, such as melting point, viscosity, and density readily can be seen by examining the phase diagrams for the hexafluorophosphate and tetrafluoroborate salts (see Figures 5.5 and 5.6, respectively). 

Sun, J. MacFarlane, D. R. Forsyth, M. A new family of ionic liquids based on the l-alkyl-2-methylpyrrolinium cation, Electrochim. Acta, 2003, 48(12), 1707-1711 Fors3dh, S. Golding, J. MacFarlane, D. R. Forsyth, M. A-methyl-iV-alkylpyrrolidinium tetrafluoroborate salts ionic solvents and solid electrolytes, Electrochim. Acta, 2001, 46(10-11), 1753-1757 Golding, J. J. Macfarlane, D. R. Spiccia, L. et al. Weak intermolecular interactions in sulfonamide salts structure of 1-ethyl-2-methyl-3-benzylimidazolium bis[(trifluoromethyl)sulfonyl]amide, Chem. Commun., 1998, 1593-1594. 

Figure 8.7 shows such a flow plot for the radical cation of the viologen species, l,l -bis(p-cyanophenyl)-4,4 -bipyridilium ( CPQ ), as the bis(tetrafluoroborate) salt in propylene carbonate solution, with the radical having been formed at a polished platinum electrode. The plot is seen to be linear, implying that, once formed, the CPQ radical cation is chemically stable. 

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