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Polyfluoroalkoxyaluminates

Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates rather than just read about it. In short: Polyfluoroalkoxyaluminates (PFAA) are weakly coordinating anions many of which are of the form [Al(ORF)4]−. Most PFAA's possesses an Al(III) center coordinated by four −ORF (RF = -CPh(CF3)2 (hfpp), -CH(CF3)2 (hfip), -C(CH3)(CF3)2 (hftb), -C(CF3)3 (pftb)) ligands, giving the anion an overall -1 charge.

Polyfluoroalkoxyaluminates — main illustration
Polyfluoroalkoxyaluminates — illustration

Key takeaways

  • Polyfluoroalkoxyaluminates belongs to chemistry; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Polyfluoroalkoxyaluminates to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Polyfluoroalkoxyaluminates from memory before moving on to harder problems.

Reference excerpt

Polyfluoroalkoxyaluminates (PFAA) are weakly coordinating anions many of which are of the form [Al(ORF)4]−. Most PFAA's possesses an Al(III) center coordinated by four −ORF (RF = -CPh(CF3)2 (hfpp), -CH(CF3)2 (hfip), -C(CH3)(CF3)2 (hftb), -C(CF3)3 (pftb)) ligands, giving the anion an overall -1 charge. The most weakly coordinating PFAA is an aluminate dimer, [F{Al(Opftb)3}2]−, which possess a bridging fluoride between two Al(III) centers. The first PFAA, [Al(Ohfpp)4]−, was synthesized in 1996 by Steven Strauss, and several other analogs have since been synthesized, including [Al(Ohfip)4]−, [Al(Ohftb)4]−, and [Al(Opftb)4]− by Ingo Krossing in 2001. These chemically inert and very weakly coordinating ions have been used to stabilize unusual cations, isolate reactive species, and synthesize strong Brønsted acids.

Synthesis Work by Strauss demonstrated that the synthesis of Li+[Al(Ohfpp)4]− could be achieved from the reaction of lithium aluminum hydride and HOhfpp. Analogous metal PFAA salts (MPFAA's) were later synthesized by Krossing using a similar synthetic pathway. LiAlH 4 + 4 HOR F ⟶ LiAl ( OR F ) 4 + 4 H 2 {\displaystyle {\ce {LiAlH4 + 4HOR_{F}-> LiAl(OR_{F})4 + 4H2}}} Reaction of lithium aluminum hydride with four equivalents of polyfluoroalcohol overnight in refluxing toluene yields the desired PFAA's . The colorless products can be precipitated from toluene in high yields on multi-gram scales by cooling at -20 °C for an hour. It can be furthered purified by sublimation.

Cation exchange and reactivity

Metal exchange While Li+[Al(Ohfpp)4]− is readily soluble in hydrocarbon solvents, presumably due to aryl substituents, Li+[Al(Ohfip)4]−, Li+[Al(Ohftb)4]−, and Li+[Al(Opftb)4]− are only sparingly soluble in common organic solvents including dichloromethane (DCM), toluene, and hexane. Their silver analogs are much more soluble however, making AgPFAA's more desirable reagents for liquid phase reactivity. LiAl ( OR F ) 4 + AgF ⟶ AgAl ( OR F ) 4 + LiF {\displaystyle {\ce {LiAl(OR_{F})4 + AgF -> AgAl(OR_{F})4 +LiF}}}

Ag+[Al(Ohfip)4]−, Ag+[Al(Ohftb)4]−, and Ag+[Al(Opftb)4]− can be synthesized via salt metathesis reactions; ultrasonication of a suspension of Li+[PFAA]− and an excess of AgF at 40 °C for 12 hours produces the final colorless products in high yields on multigram scales. Analogous M+[Al(Opftb)4]−, M = Na, K, Rb, Cs, salts can also be prepared via the same synthetic route, from the metathesis reactions of Li+[Al(Opftb)4]− with the corresponding MCl salt.

Brønsted acid chemistry Strong Brønsted acids, [H(OEt2)2]+[Al(Opftb)4]− and [H(THF)2]+[Al(Opftb)4]− , can be prepared via the reaction of Li+[Al(Opftb)4]− with two equivalents of Lewis base, Et2O or THF, and strong acid, HX (X = Cl, Br). [H(OEt2)2]+[Al(Opftb)4]− is isolable as a white powder sensitive to air and water and stable at moderately high temperatures. [H(THF)2]+[Al(Opftb)4]− can be isolated as a crystalline solid from a brown oily reside, presumably containing polymerized THF products formed upon addition of strong acid.

Li + [ Al ( OR F ) 4 ] − + 2 B + HX ⟶ [ H ( B ) 2 ] + [ Al ( OR F ) 4 ] − + LiX {\displaystyle {\ce {Li+[Al(OR_{F})4]- + 2B + HX -> [H(B)2]+[Al(OR_{F})4]- + LiX}}}

… excerpt ends here. Continue reading the full article.

Illustrations

Polyfluoroalkoxyaluminates: Space-filled crystal structure of Al(OC(CF3)3)4−. Oxygen atoms are colored red, aluminum pink, carbon gray and fluorine yellow
Space-filled crystal structure of Al(OC(CF3)3)4−. Oxygen atoms are colored red, aluminum pink, carbon gray and fluorine yellow
Polyfluoroalkoxyaluminates: Proposed resonance structure of protonated ether.[7] Recreated from source.
Proposed resonance structure of protonated ether.[7] Recreated from source.
Polyfluoroalkoxyaluminates: Crystal structure of Mn(NO)4+[Al(OC(CF3))4]− recreated from source.[12] Manganese atoms are colored purple, nitrogen blue, oxygen red, aluminum pink, carbon gray and fluorine yellow.
Crystal structure of Mn(NO)4+[Al(OC(CF3))4]− recreated from source.[12] Manganese atoms are colored purple, nitrogen blue, oxygen red, aluminum pink, carbon gray and fluorine yellow.
Polyfluoroalkoxyaluminates: Crystal Structure of [Cr(CO)6]•+[F{Al(pftb)3}2]− recreated from source.[9] Chromium atoms are colored purple, oxygen red, aluminum pink, carbon gray and fluorine yellow.
Crystal Structure of [Cr(CO)6]•+[F{Al(pftb)3}2]− recreated from source.[9] Chromium atoms are colored purple, oxygen red, aluminum pink, carbon gray and fluorine yellow.
Polyfluoroalkoxyaluminates: Synthesis of Co(I)bz2+[Al(ORF)4]− (-ORF = -OC(CF3)).[13]
Synthesis of Co(I)bz2+[Al(ORF)4]− (-ORF = -OC(CF3)).[13]

Worked examples

Example 1 — a first encounter with Polyfluoroalkoxyaluminates

Start with the simplest possible case. Write down what Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates

In research
Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates 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
Polyfluoroalkoxyaluminates is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkoxy groups, Aluminates, Non-coordinating anions, so understanding it makes those chapters shorter.
In everyday life
Look for Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Polyfluoroalkoxyaluminates means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Polyfluoroalkoxyaluminates out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polyfluoroalkoxyaluminates in simple terms?

Polyfluoroalkoxyaluminates (PFAA) are weakly coordinating anions many of which are of the form [Al(ORF)4]−. Most PFAA's possesses an Al(III) center coordinated by four −ORF (RF = -CPh(CF3)2 (hfpp), -CH(CF3)2 (hfip), -C(CH3)(CF3)2 (hftb), -C(CF3)3 (pftb)) ligands, giving the anion an overall -1 char…

Why does Polyfluoroalkoxyaluminates 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 Polyfluoroalkoxyaluminates?

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 Polyfluoroalkoxyaluminates.

Tags

  • Alkoxy groups
  • Aluminates
  • Non-coordinating anions
  • Perfluorinated compounds

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