chemistry

Organorhodium chemistry

Organorhodium chemistry 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 Organorhodium chemistry rather than just read about it. In short: Organorhodium chemistry is the chemistry of organometallic compounds containing a rhodium-carbon chemical bond, and the study of rhodium and rhodium compounds as catalysts in organic reactions. Stable organorhodium compounds and transient organorhodium intermediates are used as catalyst such as in olefin hydroformylation, olefin hydrogenation, olefin isomerization and the Monsanto process.

Key takeaways

Organorhodium 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 Organorhodium chemistry to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Organorhodium chemistry from memory before moving on to harder problems.

Reference excerpt

Organorhodium chemistry is the chemistry of organometallic compounds containing a rhodium-carbon chemical bond, and the study of rhodium and rhodium compounds as catalysts in organic reactions. Stable organorhodium compounds and transient organorhodium intermediates are used as catalyst such as in olefin hydroformylation, olefin hydrogenation, olefin isomerization and the Monsanto process.

Classification based on principal oxidation states Organometallic rhodium compounds share many characteristics with those of iridium, but less so with cobalt. Rhodium can exist in oxidation states of −3 to +5, but rhodium(I) and rhodium(III) are the more common. Rhodium(I) compounds (d8 configuration) usually occur with square planar or trigonal bipyramidal geometries, while rhodium (III) compounds (d6 configuration) typically have an octahedral geometry.

Rhodium(0) Rhodium(0) complexes are binary carbonyls, the principal examples being tetrarhodium dodecacarbonyl, Rh4(CO)12, and hexadecacarbonylhexarhodium, Rh6(CO)16. These compounds are obtained by reductive carbonylation of rhodium(III) salts or Rh2Cl2(CO)4. In contrast to the stability of the homologous Co2(CO)8, Rh2(CO)8 is very labile.

Rhodium(I) Rhodium(I) complexes are important homogeneous catalysts. Common complexes include bis(triphenylphosphine)rhodium carbonyl chloride, chlorobis(ethylene)rhodium dimer, cyclooctadiene rhodium chloride dimer, chlorobis(cyclooctene)rhodium dimer, dicarbonyl(acetylacetonato)rhodium(I), and rhodium carbonyl chloride. Although not formally organometallic, Wilkinson's catalyst (RhCl(PPh3)3), is included in the list of important catalysts. The simple olefin complexes chlorobis(ethylene)rhodium dimer, chlorobis(cyclooctene)rhodium dimer, and cyclooctadiene rhodium chloride dimer are often used as sources of "RhCl", exploiting the lability of the alkene ligands or their susceptibility to removal by hydrogenation. (η5-Cp)RhL2 are derived from Rh2Cl2L4 (L = CO, C2H4).

Rhodium(II) Unlike the prevalence of cobalt(II) complexes, compounds of rhodium(II) are rare. The sandwich compound rhodocene is one example, even it exists in equilibrium with a dimeric Rh(I) derivative. Although not organometallic, rhodium(II) acetate (Rh2(OAc)4) catalyzes cyclopropanations via organometallic intermediates. Rhodium(II) porphyrin complexes react with methane.

Rhodium(III) Rhodium is usually supplied commercially in the Rh(III) oxidation state, the main starting reagent being hydrated rhodium trichloride. The latter reacts with olefins and with CO to give organometallic complexes, often concomitant with reduction to Rh(I). Cyclopentadienyl complexes of rhodium include the half-sandwich compound pentamethylcyclopentadienyl rhodium dichloride dimer.

Rhodium(V) Strong donor ligands - hydride, silyl, boryl - are required to stabilize Rh(V). This oxidation state is invoked in borylation reactions.

Metallacycles Cyclometalated rhodium compounds constitute an important class of organometallic chemistry. Although such compounds are well documented in the literature rhodium(III) cyclometalates with azo function are spare. A typical example of this category viz. novel hexacoordinated orthometalated rhodium(III) thiolato complex trans-[Rh(C∧N∧S)Cl(PPh3)2] was synthesized from benzyl 2-(phenylazo)phenyl thioether and RhCl3·3H2O in the presence of excess PPh3 via in situ C(sp2)−H and C(sp3)−S bond scissions. This is the first example for a coordination compound of (phenylazo)thiolate ligand. The mechanism of formation of orthometalated azobenzene derivative was described to proceed via initial coordination of azo-nitrogen followed by electrophilic substitution at the pendant phenyl ring. PPh3 plays a crucial role in the C(sp3)−S cleavage process. Reductive cleavage by single electron transfer (SET) mechanism is likely to be operative for the C−S bond cleavage. Unlike analogous (phenylazo)phenolato compound the orthometalated thiolato complex exhibits a fully reversible oxidative wave at 0.82 V vs Ag/AgCl and this response is supposed to be primarily centered on the thiolato sulfur atom.

Main applications Despite its high cost, rhodium is heavily relied on as a commercial catalyst.

Acetic acid and acetic anhydride syntheses The Monsanto process is an industrial method for the making of acetic acid by catalytic carbonylation of methanol, although it has largely been supplanted by the iridium-based Cativa process.

The catalytically active species is the anion cis-[Rh(CO)2I2]−. which undergoes oxidative addition with methyl iodide. The related Tennessee Eastman acetic anhydride process affords acetic anhydride by carbonylation of methyl acetate.

CH3CO2CH3 + CO → (CH3CO)2O

Hydroformylation

Hydroformylations often rely on rhodium-based catalysts. Water-soluble catalysts have also been developed. They facilitate the separation of the products from the catalyst.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Organorhodium chemistry

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

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

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How to study Organorhodium chemistry in 20 minutes

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

Frequently asked questions

What is Organorhodium chemistry in simple terms?

Why does Organorhodium 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 Organorhodium 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 Organorhodium chemistry.