Tetrarhodium dodecacarbonyl

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IUPACName = tri-μ-carbonyl-1:2κ²"C";1:3κ²"C";2:3κ²"C"-nonacarbonyl-1κ²"C",2κ²"C",3κ²"C",4κ³"C"- ["T"_d-(13)-Δ⁴-"closo"] -
tetrarhodium(6 "Rh"—"Rh")
OtherNames = rhodium(0) carbonyl; rhodium carbonyl; rhodium dodecacarbonyl
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CASNo = 19584-30-6
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Section2 = Chembox Properties
Formula = C₁₂O₁₂Rh₄
MolarMass = 747.743 g/mol
Appearance = Red crystals
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SolubleOther = Chlorocarbons, toluene, tetrahydrofuran
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OtherCpds = Rhodium(III) chloride, Rh₆(CO)₁₆, Rh₂(CO)₄Cl₂

Tetrarhodium dodecacarbonyl is the chemical compound with the formula Rh₄(CO)₁₂. This dark-red crystalline solid is the smallest stable binary rhodium carbonyl. It is used as a catalyst in organic synthesis.

tructure, synthesis, reactions

The structure of Rh₄(CO)₁₂ is described by a tetrahedral array of four Rh atoms with nine terminal CO ligands and three bridging CO ligands. The structure can be expressed as Rh₄(CO)₉(µ-CO)₃.

It is prepared by treatment of an aqueous solution of rhodium trichloride with activated copper metal under an atmosphere of CO.cite journal | author = S. Martinengo, G. Giordano, P. Chini, G. W. Parshall, E. R Wonchoba | title = Tri-µ-carbonyl-nonacarbonyltetrarhodium | journal = Inorganic Syntheses | year = 1990 | volume = 28 | pages = 242 – 245 | editor = Robert J. Angelico | doi = 10.1002/9780470132593.ch62]

:4 RhCl₃(H₂O)₃ + 8 Cu + 22 CO → Rh₄(CO)₁₂ + 2 CO₂ + 8 Cu(CO)Cl + 4 HCl + 10 H₂O

Alternatively, the compound can be prepared by treatment of a methanolic solution of RhCl₃(H₂O)₃ with CO to afford H [RhCl₂(CO)₂] , followed by carbonylation in the presence of sodium citrate.cite journal | author = Serp, P.; Kalck, P.; Feurer, R.; Morancho, R. | title = Tri-µ-carbonyl-nonacarbonyltetrarhodium | journal = Inorganic Syntheses | year = 1998 | volume = 32 | pages = 284 – 287 | editor = Marcetta. Y. Darensbourg | doi = 10.1002/9780470132630.ch45]

The cluster undergoes thermal substitution with phosphorus ligands::Rh₄(CO)_12-n + n L → Rh₄(CO)_12-nL_n + n CO

Related metal carbonyls

Because of their relevance to hydroformylation catalysis, the metal carbonyls has been systematically studied to a high degree. The instability of Rh₂(CO)₈ has been a source of curiosity. The analogous binary carbonyl of cobalt, Co₂(CO)₈, is well known. Solutions of Rh₅(CO)₁₂ under high pressures of CO do convert to the dirhodium compound: [cite journal | author = Brown, D. T.; Eguchi, T.; Heaton, B. T.; Iggo, J. A.; Whyman, R. | title = High-pressure spectroscopic studies of reactions of the clusters [Rh₄(CO)_12–x{P(OPh)₃}_x] (x= 1–4) with carbon monoxide or syngas | journal = Journal of the Chemical Society, Dalton Transactions | year = 1991 | pages = 677 - 683 | doi = 10.1039/DT9910000677] :Rh₄(CO)₁₂ + 4 CO → 2 Rh₂(CO)₈The relative instability of Rh₂(CO)₈ conforms with a general trend: Ru(CO)₅ loses CO spontaneously to give Ru₃(CO)₁₂.

References

General reading

* King, R. B., "Rhodium: Organometallic Chemistry" Encyclopedia of Inorganic Chemistry 1994, 7, 3494.