Cyclooctadiene rhodium chloride dimer

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

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Preparation and reactions

The synthesis of Rh₂Cl₂(COD)₂ involves treatment of hydrated rhodium trichloride with 1,5-cyclooctadiene in hot, deoxygenated aqueous ethanol in the presence of sodium carbonate:^[1]

2 RhCl₃(H₂O)₃ + 2 C₈H₁₂ + 2 CH₃CH₂OH + 2 Na₂CO₃ → [RhCl(C₈H₁₂)]₂ + 2 CH₃CHO + 8 H₂O + 2 CO₂ + 4 NaCl

Rh₂Cl₂(COD)₂ is the principal source of the versatile electrophile "[Rh(COD)]⁺."

[RhCl(COD)]₂ + n L → [L_nRh(COD)]⁺Cl^- (where L = PR₃, alkene, etc.)

In this way, chiral phosphines such as "Chiraphos", "DIPAMP", "DIOP" have been attached to Rh. The resulting chiral catalysts are capable of asymmetrically hydrogenating certain prochiral alkenes.^[2]

References

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. ISBN 0-471-52619-3.
2. ^ Knowles, W. S., Advances in Synthesis and Catalysis 2003, volume 345, pages 3-13.