chemistry

Tris(pentafluorophenyl)borane

Tris(pentafluorophenyl)borane is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tris(pentafluorophenyl)borane rather than just read about it. In short: Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C6F5)3B. It is a white, volatile solid.

Key takeaways

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Reference excerpt

Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C6F5)3B. It is a white, volatile solid. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central boron atom; the BC3 core is planar. It has been described as the “ideal Lewis acid” because of its high thermal stability and the relative inertness of the B-C bonds. Related fluoro-substituted boron compounds, such as those containing B−CF3 groups, decompose with formation of B-F bonds. Tris(pentafluorophenyl)borane is thermally stable at temperatures well over 200 °C, resistant to oxygen, and water-tolerant.

Preparation Tris(pentafluorophenyl)borane is prepared using a Grignard reagent derived from bromopentafluorobenzene:

3C6F5MgBr + BCl3 → (C6F5)3B + 3MgBrCl The synthesis originally employed C6F5Li, but this reagent can detonate with elimination of LiF.

Structure The structure of tris(pentafluorophenyl)borane (BCF) was determined by gas electron diffraction. It has a propeller-like arrangement of its three pentafluorophenyl groups with a torsional angle of 40.6(3)° for the deviation of these groups from a hypothetically planar arrangement. Compared with a torsional angle of 56.8(4)° for tris(perfluoro-para-tolyl)borane, which is a stronger Lewis acid than BCF, this shows that there is some delocalization of electron density from the para-fluorine atoms to the boron atom that reduces its acidity.

Lewis acidity The most noteworthy property of this molecule is its strong Lewis acidity. Its Lewis acid strength, as quantified by experimental equilibrium constants, is by 7 orders of magnitude higher than the one of structurally analogous triphenylborane. Experimental equilibrium measurements, its AN value (Gutmann-Beckett method) as well as quantum-chemical calculations all indicate that the Lewis acidity of B(C6F5)3 is slightly lower than that of BF3 and significantly reduced compared to BCl3. B(C6F5)3 forms a strong Lewis adduct with water, which was shown to be a strong Brønsted acid having an acidity comparable to hydrochloric acid (in acetonitrile). In consequence, even traces of moisture are able to deactivate B(C6F5)3 and remaining catalytic activity might only be due to the Brønsted acidity of the water adduct.

Applications in catalysis In one application (C6F5)3B forms noncoordinating anions by removing anionic ligands from metal centers. Illustrative is a reaction that give rise to alkene polymerization catalysts where tris(pentafluorophenyl)boron is used as an activator or cocatalyst:

(C6F5)3B + (C5H5)2Zr(CH3)2 → [(C5H5)2ZrCH3]+[(C6F5)3BCH3]− In this process, the strongly coordinating methyl group transfers to the boron to expose a reactive site on zirconium. The resulting cationic zirconocene species is stabilised by the non coordinating borane anion. The exposed site on the zirconium allows for coordination of alkenes, whereupon migratory insertion into the remaining carbon-methyl ligand gives rise to a propyl ligand this process continues resulting in the growth of a polymer chain. This reagent has led to the development of immobilised catalyst/activator species; where the catalyst/activator is immobilised on an inert inorganic support such as silica. Tris(pentafluorophenyl)borane is also capable of abstracting hydride to give [(C6F5)3BH]−, and it catalyzes hydrosilylation of aldehydes. Otherwise (C6F5)3B binds to a wide range of Lewis bases, even weak ones. The compound is hygroscopic, forming the trihydrate [(C6F5)3BOH2](H2O)2, wherein one water in coordinated to boron and the other two waters are hydrogen-bonded to the coordinated water. Related compounds are pentafluorophenylboron halides.

Frustrated Lewis pair Tris(pentafluorophenyl)borane is a key reagent leading to the concept of frustrated Lewis pairs. The combination of BCF and bulky basic phosphines, such as tricyclohexylphosphine (PCy3) cleaves H2:

(C6F5)3B + PCy3 + H2 → (C6F5)3BH− + HPCy3+ Many related phosphines, boranes, and substrates participate in related reactions.

Other reactions (C6F5)3B was used to prepare a compound containing a Xe-C bond:

(C6F5)3B + XeF2 → [C6F5Xe]+[(C6F5)2BF2]− Upon reaction with pentafluorophenyllithium, the salt of the noncoordinating anion lithium tetrakis(pentafluorophenyl)borate is formed.

(C6F5)3B + C6F5Li → Li[(C6F5)4B] B(C6F5)3 reacts with dimesitylphosphine to give the zwitterionic phosphonic-boronate (mes = C6H2Me3):

(C6F5)3B + mes2PH → (C6F5)2B(F)−C6F4−P(H)mes2 This zwitterionic salt can be converted to a system that reversibly binds molecular H2:

(C6F5)2B(F)−C6F4−P(H)mes2 + Me2SiHCl → (C6F5)2B(H)−C6F4−P(H)mes2 + Me2SiFCl (C6F5)2B(H)−C6F4−P(H)mes2 → (C6F5)2B−C6F4−Pmes2 + H2

References

Extra reading Lawson, James R.; Melen, Rebecca L. (3 February 2017). "Tris(pentafluorophenyl)borane and Beyond: Modern Advances in Borylation Chemistry". Inorganic Chemistry. 56 (15): 8627–8643. doi:10.1021/acs.inorgchem.6b02911. PMID 28157303.

Illustrations

Worked examples

Example 1 — a first encounter with Tris(pentafluorophenyl)borane

Start with the simplest possible case. Write down what Tris(pentafluorophenyl)borane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tris(pentafluorophenyl)borane before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tris(pentafluorophenyl)borane ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tris(pentafluorophenyl)borane

In research: Tris(pentafluorophenyl)borane appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tris(pentafluorophenyl)borane in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tris(pentafluorophenyl)borane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acid catalysts, Organoboranes, Pentafluorophenyl compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Tris(pentafluorophenyl)borane outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tris(pentafluorophenyl)borane in 20 minutes

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Frequently asked questions

What is Tris(pentafluorophenyl)borane in simple terms?

Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C6F5)3B. It is a white, volatile solid.

Why does Tris(pentafluorophenyl)borane matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tris(pentafluorophenyl)borane?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tris(pentafluorophenyl)borane.