Organozinc chemistry

Key takeaways

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

Reference excerpt

Organozinc chemistry is the study of the physical properties, synthesis, and reactions of organozinc compounds, which are organometallic compounds that contain carbon (C) to zinc (Zn) chemical bonds. Organozinc compounds were among the first organometallic compounds made. They are less reactive than many other analogous organometallic reagents, such as Grignard and organolithium reagents. In 1848 Edward Frankland prepared the first organozinc compound, diethylzinc, by heating ethyl iodide in the presence of zinc metal. This reaction produced a volatile colorless liquid that spontaneous combusted upon contact with air. Due to their pyrophoric nature, organozinc compounds are generally prepared using air-free techniques. They are unstable toward protic solvents. For many purposes they are prepared in situ, not isolated, but many have been isolated as pure substances and thoroughly characterized. Organozincs can be categorized according to the number of carbon substituents that are bound to the metal.

Diorganozinc (R2Zn): A class of organozinc compounds in which two alkyl ligands. These may be further divided into subclasses depending on the other ligands attached Heteroleptic (RZnX): Compounds which an electronegative or monoanionic ligand (X), such as a halide, is attached to the zinc center with another alkyl or aryl substituent (R). Ionic organozinc compounds: This class is divided into organozincates (RnZn−) and organozinc cations (RZnL+n).

Bonding In its coordination complexes zinc(II) adopts several coordination geometries, commonly octahedral, tetrahedral, and various pentacoordinate geometries. These structural flexibility can be attributed to zinc's electronic configuration [Ar]3d104s2. The 3d orbital is filled, and therefore, ligand field effects are nonexistent. Coordination geometry is thus determined largely by electrostatic and steric interactions. In organozinc compounds, carbon and zinc atoms form a polar covalent bond. The bond is polarized toward carbon due to the differences in electronegativity values (carbon: 2.5 & zinc: 1.65), but still about 85% covalent, comparable to a carbon-tin bond. Because zinc has a large atomic radius and low electron deficiency, organozinc compounds rarely saturate zinc's coordination sphere. Instead, they are usually two- or three-coordinate, reflecting strong donation from the carbanionic ligands. Diorganozinc species complex ethereal solvents only weakly, and bridging alkyl or aryl groups are rare. Exceptions are Ph2Zn and certain metal clusters:

Organozinc complexes with formula R2Zn are monomeric and linear at the zinc atom, generating sp-hybridization in the molecular orbitals. The symmetric molecules have no dipole moment, and dissolve easily in nonpolar solvents like cyclohexane. When a halogen ligand is added to the zinc atom, the molecule is polarized and both the acceptor and donor character of zinc is enhanced, allowing for aggregation.

Synthesis Several methods exist for the generation of organozinc compounds. Commercially available diorganozinc compounds are dimethylzinc, diethylzinc and diphenylzinc, but these reagents are expensive and difficult to handle.

From zinc metal Frankland's original synthesis of diethylzinc involves the reaction of ethyl iodide with zinc metal. Similar to formation of a Grignard reagent, the zinc must be activated to facilitate this redox reaction, and ethereal solvents accelerate the reaction by stabilizing the product. One of such activated form of zinc employed by Frankland is zinc-copper couple:

2 EtI + 2 Zn0 → Et2Zn + ZnI2 Alternatively, in situ reduction of ZnCl2 with potassium generates Riecke zinc, another activated form of zinc:

ZnCl 2 + 2 K → − 2 KCl THF Zn 0 ⏞ Riecke zinc + R − X → 20 − 60 ∘ C THF R − Zn − I { R : Allyl, Aryl, Alkyl, Benzyl X : Bromide, Iodide {\displaystyle {\ce {{ZnCl2}+2K->[{\ce {THF}}][{\ce {-2KCl}}]}}\overbrace {\ce {Zn^{0}}} ^{\ce {Riecke\ zinc}}+{\ce {R-X->[{\ce {THF}}][20-60^{\circ }{\ce {C}}]R-Zn-I}}\qquad {\begin{cases}\mathbf {R} :&{\text{Allyl, Aryl, Alkyl, Benzyl}}\\\mathbf {X} :&{\text{Bromide, Iodide}}\end{cases}}}

In some cases, a weak Lewis acid, suffices to activate the zinc metal. For example, in the following synthesis, 1,2-dibromoethane and trimethylsilyl chloride catalyze formation of the final organozinc through transmetallation, but a key ingredient is lithium chloride, which quickly forms a soluble adduct with the bromoethylzinc intermediate, removing it from the metal surface:

… excerpt ends here. Continue reading the full article.

Illustrations

Organozinc chemistry: Organozinc chemistry — Organozinc chemistry

Worked examples

Example 1 — a first encounter with Organozinc chemistry

Start with the simplest possible case. Write down what Organozinc chemistry 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 Organozinc chemistry 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 Organozinc chemistry 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 Organozinc chemistry

In research: Organozinc chemistry 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 Organozinc chemistry 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: Organozinc chemistry is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organozinc compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Organozinc chemistry 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.

How to study Organozinc chemistry in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Organozinc chemistry 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 Organozinc chemistry out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Organozinc chemistry in simple terms?

Organozinc chemistry is the study of the physical properties, synthesis, and reactions of organozinc compounds, which are organometallic compounds that contain carbon (C) to zinc (Zn) chemical bonds. Organozinc compounds were among the first organometallic compounds made.

Why does Organozinc chemistry 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 Organozinc chemistry?

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 Organozinc chemistry.