Tetra fluoroborate ion

One additional term occurs ui this Bom-Haber cycle the formation of the tetra-fluoroborate ion in the gas phase ... 

In the following reaction of tetrafluoroboric acid, HBF4, with the acetate ion, C2H302, the formation of tetra-fluoroborate ion, Bp4, and acetic acid, HC2H3O2 is favored. 

There is, however, another possible explanation. For relatively weak complexes, as in these cases, a complex other than one of the insertion type may form in solution, for example a charge-transfer complex. An early observation which may indicate the formation of other types of complexes was reported by Bartsch and Juri (1980), but not interpreted the dediazoniation rate for 4-tert-butylbenzenediazonium tetra-fluoroborate in 1,2-dichloroethane decreases by 12% in the presence of one equivalent of 15-crown-5, a host compound which does not form insertion complexes. Kuokkanen and Virtanen (1979) also observed some stabilization towards dediazoniation of 2-toluenediazonium ion by 18-crown-6, even though, for steric reasons, an insertion-type complex is hardly possible in this case. 

Fyfe et al. (355) were able to produce a very informative 13C CP/MAS NMR spectrum of the triphenylmethyl carbonium ion by using the tetra-fluoroborate counterion and by employing simultaneous 19F and H decoupling during spectral acquisition (see Fig. 81). The nonequivalence of the ortho and meta carbons is readily seen in the spectrum. 

The steric effects of the substituents, such as in 3,5-dialkylpyrazoles, may induce the coordination of small ligands or counterions that usually do not coordinate to transition metal ions. This behaviour is believed to be responsible for the unusual decomposition of transition metal tetra-fluoroborates in the presence of such ligands.43 Otherwise, the coordination number changes, resulting in, for example, square-planar Ni11 (low-spin) complexes, even with rather weak ligands such as 1,2-dimethylimidazole.44... 

These methylene-bridged complexes III are extremely robust, air-stable substances. We have sought without success to effect insertions into the Pd-C bonds. The complexes are unreactive toward carbon monoxide (at 5 atm at 30°C) or sulfur dioxide. Reaction with methyl isocyanide or pyridine results in displacement of the terminal halide ions and produces cations that have been isolated as hexa-fluorophosphate salts [Pd2(dpm)2( -CH2)(CNCH3)2][PF6]2( (CN) = 2217 cm-1) and [Pd2(dpm)2(/Lt-CH2)(py)2][PF6]2. Treatment of III with fluoroboric or trifluoroacetic acid slowly results in the protonation of the methylene group which is converted into a terminal methyl group. The resulting brown complex, which has been isolated as its tetra-fluoroborate salt has been shown by H-l and P-31 NMR spectroscopy and X-ray crystallography to have Structure IV. 

The crystal structure for pentamethylcyclopentadienyltin(II) tetra-fluoroborate has been determined (23) and is shown in Fig. 4. The Sn—C bonds are all equal and quite short at 2.462 A. Apparently, the Sn—Cp bonding is stronger in the +1 ion than in the neutral SnCp2 species. Each tin atom is associated to two fluorine atoms of the BF4 counterion at distances of 2.97 and 2.99 A. 

Dienes are generally much less reactive when coordinated to transition metals than when in an uncoordinated state. An important discovery was thus made by Fischer and Fischer (86) in 1960 when they found that cyclo-hexadiene-iron tricarbonyl (XV) (formed from 1,3-cyclohexadiene and iron pentacarbonyl) undergoes hydride ion abstraction by triphenylmethyl tetrafluoroborate to form 7r-cyclohexadienyl-iron tricarbonyl tetra-fluoroborate (XVI) ... 

Another way of generating arenium ions based on dihydroaromatic compounds is to break off, with a pair of electrons, a substituent located at one of the ring sp -hybridized carbon atoms. G. Olah et al. have used this method to obtain tetra-fluoroborate of the methylbenzenium ion by the action of AgBF on the bromination product of l-methylcyclohexa-l,4-diene at —60 °C. 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

Transition metal cations are usualty octahedrally solvent coordinated according to spectral evidence. When competitive ligands, such as bromide, chloride or azide ions are added to the solutions of transition metal perchlorates or tetra-fluoroborates, replacement of the solvent molecules together with the coordination changes involved has been followed by spectrophotometric, conductometric and potentiometric techniques (Table 67). 

The electrolyte solution consists of a lithium salt in an organic solvent. Commonly used salts include lithium hexafluorophosphate, lithium perchlorate, lithium tetra-fluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, and lithium tetraphen)dborate. Organic solvents used in the electrolyte solution are ethylene carbonate, dieth)d carbonate, dimethyl carbonate, methyl ethyl carbonate, and propylene carbonate, to name the most important ones. When a lithium ion battery is charged, the positive lithium ions move from the positive electrode to the negative one. The process to insert the lithium ions into the graphite electrode is called intercalation. When the cell is discharging, the reverse occurs. 

Dissolved ionophores are initially completely dissociated and the ions are solvated. However, association to ion pairs, triple irms, or even higher aggregates may occur, depending oti solvent properties (e.g., permittivity) or electrolyte concentration. Equation 2 shows the different association steps and the different species for lithium tetra fluoroborate in dimethoxyethane (DME) as an example (solvated ions, ion pair, and triple ions) [4, 5]... 

An elimination-addition mechanism has also been invoked for the nucleophilic substitution of cyclohexenyliodonium salts with acetate ion. For example, the reaction of either the 4- or 5-substituted cyclohex-l-enyl(phenyl)iodonium tetra-fluoroborate (31 or 32 respectively) with tetrabutylainmonium acetate in aprotic solvents gives the ipso and cine acetate substitution products (33 and 34 and vice-versa, respectively) in almost the same ratio (Scheme 23). These results were consistent with an elimination-addition mechanism involving 4-substituted cyclohexyne 35 as a common intermediate. The presence of a cyclohexyne intermediate was confirmed by deuterium labelling and trapping studies leading to [4-l-2]-cycloaddition products. 

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