Pentamethylcyclopentadienyl rhodium dichloride dimer

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.

Pentamethylcyclopentadienyl rhodium dichloride dimer

Names
IUPAC name Di-μ-chloro-bis[chloro(pentamethylcyclopentadienyl)rhodium(III)]
Other names Dichloro(pentamethylcyclopentadienyl)rhodium(III)
Identifiers
CAS Number	12354-85-7  Y
3D model (JSmol)	Interactive image
ChemSpider	26583494
PubChem CID	16212157
InChI InChI=1S/2C10H15.4ClH.2Rh/c2*1-6-7(2)9(4)10(5)8(6)3;;;;;;/h2*1-5H3;4*1H;;/q;;;;;;2* 2/p-4 Key: QNIVKTTWBMFSBR-UHFFFAOYSA-J
SMILES c1(C)=c(C)c(C)=c(C)c1(C)[Rh](Cl)(Cl1)Cl[Rh](Cl)1C1(C)C(C)=C(C)C(C)=C1C
Properties
Chemical formula	C20H30Cl4Rh2
Molar mass	618.07 g·mol−1
Appearance	red solid
Solubility in water	dichloromethane, chloroform
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H312, H315, H319, H332, H334, H335
Precautionary statements	P261, P264, P270, P271, P280, P285, P301 P312, P302 P352, P304 P312, P304 P340, P304 P341, P305 P351 P338, P312, P321, P322, P330, P332 P313, P337 P313, P342 P311, P362, P363, P403 P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Structure and preparation

The compound has idealized C_2h symmetry. Each metal centre is pseudo-octahedral.

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

Synthesis of [Cp*RhCl₂]₂ using 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.

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/C19680001304.1304-1305&rft.date=1968&rft_id=info:doi/10.1039/C19680001304&rft.aulast=Kang&rft.aufirst=Jung W.&rft.au=Mosley, K.&rft.au=Maitlis, Peter M.&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">
• 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/ja01014a063.3259-3261&rft.date=1968&rft_id=info:doi/10.1021/ja01014a063&rft.aulast=Kang&rft.aufirst=Jung W.&rft.au=Maitlis, Peter M.&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">
• 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.196804672.467-468&rft.date=1968&rft_id=info:doi/10.1002/anie.196804672&rft.aulast=Criegee&rft.aufirst=Rudolf&rft.au=Grüner, H.&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">
• 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/ja01050a008.5970-5977&rft.date=1969&rft_id=info:doi/10.1021/ja01050a008&rft.aulast=Kang&rft.aufirst=Jung W.&rft.au=Moseley, K.&rft.au=Maitlis, Peter M.&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">
• 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 9783131791610.148-149&rft.pub=Georg Thieme Verlag&rft.date=1996&rft.isbn=9783131791610&rft.aulast=Herrmann&rft.aufirst=Wolfgang A.&rft.au=Zybill, Christian&rft_id=https://books.google.com/books?id=dlGGAwAAQBAJ&pg=PA148&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">
• 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 9780323154703.116-117&rft.pub=Academic Press&rft.date=1974&rft.isbn=9780323154703&rft.aulast=Heck&rft.aufirst=Richard F.&rft_id=https://books.google.com/books?id=VmE2BtDmHjYC&pg=PA116&rfr_id=info:sid/en.wikipedia.org:Pentamethylcyclopentadienyl rhodium dichloride dimer" class="Z3988">