Tetrarhodium dodecacarbonyl

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Tetrarhodium dodecacarbonyl
Rh4(CO)12.png
Tetrarhodium-dodecacarbonyl-from-xtal-173K-3D-balls-A.png
Names
IUPAC names
tri-μ-carbonyl-1:2κ2C;1:3κ2C;2:3κ2C-nonacarbonyl- 1κ2C,2κ2C,3κ2C,4κ3C-[Td-(13)-Δ4-closo]-
tetrarhodium(6 RhRh)
Other names
rhodium(0) carbonyl; rhodium carbonyl; rhodium dodecacarbonyl
Identifiers
19584-30-6 YesY
Properties
Rh4(CO)12
Molar mass 747.743 g/mol
Appearance Red crystals
Solubility Chlorocarbons, toluene, tetrahydrofuran
Vapor pressure {{{value}}}
Related compounds
Related compounds
Rhodium(III) chloride, Rh6(CO)16, Rh2(CO)4Cl2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.

Structure, 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.[1]

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.[2]

The cluster undergoes thermal substitution with phosphorus ligands:

Rh4(CO)12-n + n L → Rh4(CO)12-nLn + 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 Rh4(CO)12 under high pressures of CO convert to the dirhodium compound:[3]

Rh4(CO)12 + 4 CO → 2 Rh2(CO)8

Unlike Co2(CO)8, the main isomer of Rh2(CO)8 features only terminal CO ligands. The relative instability of Rh2(CO)8 is analogous to the tendency of Ru(CO)5 to convert to Ru3(CO)12.

References

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General reading

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