Imidazolium and formamidinium salts, ionic liquids and precursors to stable carbenes, are often isolated as tetrafluoroborates. BF 4Īn electrochemical cycle involving ferrous/ferric tetrafluoroborate is being used to replace thermal smelting of lead sulfide ores by the Doe Run Company. Transition metal nitrile complexes, e.g.Most other transition metal tetrafluoroborates only exist as solvates of water, alcohols, ethers, or nitriles. Silver tetrafluoroborate and thallium tetrafluoroborate are convenient halide abstracting agents (although the thallium salt is highly toxic).Bromonium and iodonium species, including py 2X + (X = Br X = I: Barluenga's reagent) and Ar 2I + ( diaryliodonium salts).Selectfluor, a fluorination agent, and other N–F electrophilic fluorine sources.NO + a one-electron oxidizing agent and nitrosylation reagent.(Et 2O) nģ, the strongest commercial alkylating agents.Solvated proton (H + (solv.), fluoroboric acid), including H +.Potassium fluoroborate is obtained by treating potassium carbonate with boric acid and hydrofluoric acid.ī(OH) 3 + 4 HF → HBF 4 + 3 H 2O 2 HBF 4 + K 2CO 3 → 2 KBF 4 + H 2CO 3įluoroborates of alkali metals and ammonium ions crystallize as water-soluble hydrates with the exception of potassium, rubidium, and cesium.įluoroborate is often used to isolate highly electrophilic cations. Tin, lead, copper, and nickel fluoroborates are prepared through electrolysis of these metals in a solution containing HBF 4. Transition and heavy metal fluoroborates are produced in the same manner as other fluoroborate salts the respective metal salts are added to reacted boric and hydrofluoric acids. Ether and halopyridine adducts of HBF 4 have been reported to be effective reagents for the hydrofluorination of alkynes. The Balz–Schiemann reaction for the synthesis of aryl fluorides is the best known example of such a reaction. ĭespite the low reactivity of the tetrafluoroborate anion in general, BF −Ĥ serves as a fluorine source to deliver an equivalent of fluoride to highly electrophilic carbocationic species to generate carbon–fluorine bonds.
For instance, the gold complex was found crystallographically to contain two Au–F–B bridges. Moreover, in other cases of ostensibly "cationic" complexes, the fluorine atom in fact acts as a bridging ligand between boron and the cationic center. Įxtremely reactive cations such as those derived from Ti, Zr, Hf, and Si do in fact abstract fluoride from BF −Ĥ is not an "innocent" anion and less coordinating anions (e.g., SbF 6 –, BARF –, or –) must be employed. Illustrative of a fluoroborate salt is (BF 4) 2, a kinetically labile octahedral complex, which is used as a source of Ni 2+. Related to BF −Ħ, both of which are even more stable toward hydrolysis and other chemical reactions and whose salts tend to be more lipophilic. In addition to the weakly coordinating nature of the anion, BF −Ĥ salts are often more soluble in organic solvents (lipophilic) than the related nitrate or halide salts. BF −Ĥ owes its inertness to two factors: (i) it is symmetrical so that the negative charge is distributed equally over four atoms, and (ii) it is composed of highly electronegative fluorine atoms, which diminish the basicity of the anion. Thus, when using salts of BF −Ĥ, one can usually assume that the cation is the reactive agent and this tetrahedral anion is inert. With a formula weight of 86.8, BF –Ĥ is also conveniently the smallest weakly coordinating anion from the point of view of equivalent weight, often making it the anion of choice for preparing cationic reagents or catalysts for use in synthesis, in the absence of other substantial differences in chemical or physical factors.Ĥ anion is less nucleophilic and basic (and therefore more weakly coordinating) than nitrates, halides or even triflates. Safety considerations, however, overshadow this inconvenience. Disadvantages to BF −Ĥ include its slight sensitivity to hydrolysis and decomposition via loss of a fluoride ligand, whereas ClO −Ĥ does not suffer from these problems.
With organic compounds, especially amine derivatives, ClO −Ĥ forms potentially explosive derivatives. 1 As an anion in inorganic and organic chemistryĪs an anion in inorganic and organic chemistry Ĥ in the laboratory as a weakly coordinating anion.
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