chemistry

Pentamethylcyclopentadienyl rhodium dichloride dimer

Pentamethylcyclopentadienyl rhodium dichloride dimer 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 Pentamethylcyclopentadienyl rhodium dichloride dimer rather than just read about it. In short: Pentamethylcyclopentadienyl rhodium dichloride dimer is an organometallic compound with the formula [(C5(CH3)5RhCl2)]2, commonly abbreviated [Cp*RhCl2]2 This dark red air-stable diamagnetic solid is a reagent in organometallic chemistry. Structure and preparation The compound has idealized C2h symmetry.

Key takeaways

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Reference excerpt

Pentamethylcyclopentadienyl rhodium dichloride dimer is an organometallic compound with the formula [(C5(CH3)5RhCl2)]2, commonly abbreviated [Cp*RhCl2]2 This dark red air-stable diamagnetic solid is a reagent in organometallic chemistry.

Structure and preparation The compound has idealized C2h symmetry. Each metal centre is pseudooctahedral. The compound is prepared by the reaction of rhodium trichloride trihydrate and pentamethylcyclopentadiene in hot methanol, from which the product precipitates:

2 C5(CH3)5H + 2 RhCl3(H2O)3 → [(C5(CH3)5)RhCl2]2 + 2 HCl + 6 H2O It was first prepared by the reaction of hydrated rhodium trichloride with hexamethyl Dewar benzene

This complex was first prepared from hexamethyl Dewar benzene and RhCl3(H2O)3. The hydrohalic acid necessary for the ring-contraction rearrangement is generated in situ in methanolic solutions of the rhodium salt, and the second step has been carried out separately, confirming this mechanistic description. The reaction occurs with the formation of 1,1-dimethoxyethane, CH3CH(OCH3)2, and hexamethylbenzene is produced by a side reaction. This rhodium(III) dimer can be reduced with zinc in the presence of CO to produce the rhodium(I) complex [Cp*Rh(CO)2].

Reactions Reductive carbonylation gives [Cp*Rh(CO)2]. The Rh-μ-Cl bonds are labile and cleave en route to a variety of adducts of the general formula Cp*RhCl2L. Treatment with silver ions in polar coordinating solvents causes precipitation of silver(I) chloride, leaving a solution containing dications of the form [Cp*RhL3]2+ (L = H2O, MeCN). The chemistry is similar to that of the analog pentamethylcyclopentadienyl iridium dichloride dimer.

References

Further reading (early literature) Kang, Jung W.; Mosley, K.; Maitlis, Peter M. (1968). "Mechanisms of Reactions of Dewar Hexamethylbenzene with Rhodium and Iridium Chlorides". Chem. Commun. (21): 1304–1305. doi:10.1039/C19680001304. Kang, Jung W.; Maitlis, Peter M. (1968). "Conversion of Dewar Hexamethylbenzene to Pentamethylcyclopentadienylrhodium(III) Chloride". J. Am. Chem. Soc. 90 (12): 3259–3261. doi:10.1021/ja01014a063. Criegee, Rudolf; Grüner, H. (1968). "Acid-catalyzed Rearrangements of Hexamethyl-prismane and Hexamethyl-Dewar-benzene". Angew. Chem. Int. Ed. 7 (6): 467–468. doi:10.1002/anie.196804672. Kang, Jung W.; Moseley, K.; Maitlis, Peter M. (1969). "Pentamethylcyclopentadienylrhodium and -iridium halides. I. Synthesis and properties". J. Am. Chem. Soc. 91 (22): 5970–5977. doi:10.1021/ja01050a008. Herrmann, Wolfgang A.; Zybill, Christian (1996). "Bis{(μ-chloro)[chloro(η-pentamethylcyclopentadienyl)rhodium]} — {Rh(μ-Cl)Cl[η-C5(CH3)5]}2". In Herrmann, Wolfgang A.; Salzer, Albrecht (eds.). Synthetic Methods of Organometallic and Inorganic Chemistry – Volume 1: Literature, Laboratory Techniques, and Common Starting Materials. Georg Thieme Verlag. pp. 148–149. ISBN 9783131791610. Heck, Richard F. (1974). "Reactions of Dienes Trienes and Tetraenes with Transition Metal Compounds". Organotransition Metal Chemistry: A Mechanistic Approach. Academic Press. pp. 116–117. ISBN 9780323154703.

Illustrations

Worked examples

Example 1 — a first encounter with Pentamethylcyclopentadienyl rhodium dichloride dimer

Start with the simplest possible case. Write down what Pentamethylcyclopentadienyl rhodium dichloride dimer 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 Pentamethylcyclopentadienyl rhodium dichloride dimer 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 Pentamethylcyclopentadienyl rhodium dichloride dimer 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 Pentamethylcyclopentadienyl rhodium dichloride dimer

In research: Pentamethylcyclopentadienyl rhodium dichloride dimer 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 Pentamethylcyclopentadienyl rhodium dichloride dimer 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: Pentamethylcyclopentadienyl rhodium dichloride dimer is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chloro complexes, Dimers (chemistry), Organorhodium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Pentamethylcyclopentadienyl rhodium dichloride dimer 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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Frequently asked questions

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