Cyclooctadiene rhodium chloride dimer

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Cyclooctadiene rhodium chloride dimer
Cyclooctadiene-rhodium-chloride-dimer-2D-skeletal.png
Cyclooctadiene-rhodium-chloride-dimer-3D-balls.png
Names
IUPAC names
di-μ-chlorido-
bis[η22-(cycloocta-1,5-diene)rhodium]
Other names
Cyclooctadiene rhodium chloride dimer
Identifiers
12092-47-6 YesY
ChemSpider 21171524 YesY
Jmol-3D images Image
Properties
C16H24Cl2Rh2
Molar mass 493.0806 g/mol
Density 1.93 g/cm3
Melting point 243 °C (469 °F; 516 K)
Solubility in other solvents dichloromethane
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

Cyclooctadiene rhodium chloride dimer is the organorhodium compound with the formula Rh2Cl2(C8H12)2, commonly abbreviated [RhCl(COD)]2 or Rh2Cl2(COD)2. This yellow-orange, air-stable compound is a widely used precursor to homogeneous catalysts.[1]

Preparation and reactions[edit]

The synthesis of [RhCl(COD)]2 involves heating a solution of hydrated rhodium trichloride with 1,5-cyclooctadiene in aqueous ethanol in the presence of sodium carbonate:[1]

2 RhCl3.3(H2O) + 2 COD + 2 CH3CH2OH + 2 Na2CO3 → [RhCl(COD)]2 + 2 CH3CHO + 8 H2O + 2 CO2 + 4 NaCl

[RhCl(COD)]2 is principally used as a source of the electrophile "[Rh(COD)]+."

[RhCl(COD)]2 + n L → [LnRh(COD)]+Cl (where L = PR3, alkene, etc. and n = 2 or 3)

In this way, chiral phosphines such as chiraphos, DIPAMP, and DIOP have been attached to Rh. The resulting chiral catalysts are capable of asymmetrically hydrogenating certain prochiral alkenes.[2] A closely related but still more reactive complex is chlorobis(cyclooctene)rhodium dimer.

Structure[edit]

The molecule consists of a pair of square planar Rh centers bound to a 1,5-cyclooctadiene and two chloride ligands that are shared between the Rh centers. The Rh2Cl2 core is also approximately planar,[3] in contrast to the highly bent structure of cyclooctadiene iridium chloride dimer where the dihedral angle is 86°.

References[edit]

  1. ^ a b Giordano, G.; Crabtree, R. H. “Di-μ-chloro-bis(η4-1,5-cyclooctadiene)dirhodium(I)” Inorganic Syntheses, 1990, volume 28, pages 88-90. doi:10.1002/9780470132593.ch22
  2. ^ W. S. Knowles (2003). "Asymmetric Hydrogenations (Nobel Lecture 2001)". Advances in Synthesis and Catalysis 345 (1–2): 3. doi:10.1002/adsc.200390028. 
  3. ^ "Di-μ-chloro-bis[(cis,cis-η4-1,5-cyclooctadiene)rhodium(I)]: a redetermination" De Ridder, Kirk J. A. Acta Crystallographica, Section C: Crystal Structure Communications 1994, C50, 1569-72. doi:10.1107/S0108270194001459