chemistry

White catalyst

White catalyst 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 White catalyst rather than just read about it. In short: The White catalyst is a transition metal coordination complex named after the chemist by whom it was first synthesized, M. Christina White, a professor at the University of Illinois.

Key takeaways

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

Reference excerpt

The White catalyst is a transition metal coordination complex named after the chemist by whom it was first synthesized, M. Christina White, a professor at the University of Illinois. The catalyst has been used in a variety of allylic C-H functionalization reactions of α-olefins. In addition, it has been shown to catalyze oxidative Heck reactions.

Preparation This compound is commercially available. It may be prepared by oxidation of 1,2-bis(phenylthio)ethane to the sulfoxide, followed by reaction with palladium acetate.

Mechanism of allylic C-H acetoxylation The reaction mechanism of allylic C-H acetoxylation has been studied. The first step in the catalytic cycle is cleavage of the allylic C-H bond. The sulfoxide ligand is thought to promote this step by generating a highly electrophilic, possibly cationic palladium species in situ. This species coordinates to the alkene and acidifies the adjacent C-H bond, which allows acetate to abstract the proton and forms a π-allyl palladium complex (II). Subsequently, a π-acid such as benzoquinone coordinates to the palladium, activating the π-allyl complex to nucleophilic attack (III). A nucleophile, in this case acetate, attacks to reductively eliminate palladium, generating the product and palladium(0) (IV). The palladium(0) is reoxidized to palladium(II) by benzoquinone and the sulfoxide ligand reassociates, closing the catalytic cycle.

Allylic esterification The White catalyst was originally developed for use in a branched allylic acetoxylation reaction. An enantioselective version of this reaction was subsequently reported, using chromium(III) salen fluoride as a chiral cocatalyst. A macrolactonization reaction based on the branched allylic esterification was developed for the preparation of 14- to 19-membered macrolides. This method was applied to the total synthesis of 6-deoxyerythronolide B. In addition to acetate, a wide variety of carboxylic acids may be employed as nucleophiles in the branch allylic esterification reaction. As the first step in an esterification/Heck sequence, aliphatic and aromatic carboxylates were demonstrated, including amino acids.

Allylic amination The White catalyst can effect both branched and linear regioselective allylic C-H aminations. In order to promote nucleophilic attack at the internal terminus of the π-allyl to generate branched product, a tethered N-sulfonyl carbamate nucleophile is used. This strategy has been applied to the synthesis of 1,2 and 1,3-amino alcohols. The amination proceeds with high yields and good diastereoselectivity, and the products may be readily elaborated to amino acids and other synthetic intermediates and natural products. Key to the development of the reaction was identification of a very acidic nitrogen nucleophile with a pKa close to acetic acid, as more basic nucleophiles divert reactivity to aminopalladation. The intermolecular version of the allylic C-H amination is also known. Using methyl N-tosyl carbamate nucleophile, the linear E-allylic amine products are obtained from α-olefin substrates. It has been shown that functionalization of the π-allyl intermediate may be promoted by chromium(III) salen chloride activation of the electrophile, or Hunig's base activation of the nucleophile.

Allylic alkylation In 2008, simultaneous publications described the allylic C-H alkylation of allylarene substrates. These reactions were catalyzed by the White catalyst or by an earlier version of the complex bearing benzyl substituents on the sulfoxide in place of phenyl. It was demonstrated that an additional sulfoxide ligand, dimethylsulfoxide (DMSO), was essential for promoting functionalization of the π-allyl intermediate; the bis-sulfoxide ligand alone was unable to complete the catalytic cycle.

Heck reaction The White catalyst has been found to be an effective catalyst for an oxidative version of the classic Heck reaction. Rather than performing allylic C-H cleavage—a relatively slow process—the catalyst quickly transmetallates with a boronic acid. This aryl palladium intermediate undergoes a 1,2-addition across the alkene double bond. β-Hydride elimination releases the product. The oxidative Heck was originally reported as a sequential process following allylic C-H esterification. It was subsequently demonstrated as a stand-alone method for a broad range of α-olefin substrates. The regioselectivity of the reaction is controlled by directing groups such as carbonyls, alcohols and amines.

References

Illustrations

Worked examples

Example 1 — a first encounter with White catalyst

Start with the simplest possible case. Write down what White catalyst 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 White catalyst 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 White catalyst 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 White catalyst

In research: White catalyst 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 White catalyst 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: White catalyst is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acetates, Catalysts, Organometallic chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for White catalyst 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 White catalyst in 20 minutes

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

Frequently asked questions

What is White catalyst in simple terms?

The White catalyst is a transition metal coordination complex named after the chemist by whom it was first synthesized, M. Christina White, a professor at the University of Illinois.

Why does White catalyst 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 White catalyst?

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 White catalyst.