Cyclooctadiene rhodium chloride dimer

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]

Cyclooctadiene rhodium chloride dimer

Names
IUPAC name di-μ-chlorido-bis[η2,η2-(cycloocta-1,5-diene)rhodium]
Other names Cyclooctadiene rhodium chloride dimer
Identifiers
CAS Number	12092-47-6 Y
3D model (JSmol)	Interactive image
ChemSpider	21171524 Y
ECHA InfoCard	100.031.949
EC Number	235-157-6
PubChem CID	6436379
CompTox Dashboard (EPA)	DTXSID20923606
InChI InChI=1S/2C8H12.2ClH.2Rh/c2*1-2-4-6-8-7-5-3-1;;;;/h2*1-2,7-8H,3-6H2;2*1H;;/q;;;;2*+1/p-2/b2*2-1-,8-7-;;;; Y Key: QSUDXYGZLAJAQU-MIXQCLKLSA-L Y InChI=1/2C8H12.2ClH.2Rh/c2*1-2-4-6-8-7-5-3-1;;;;/h2*1-2,7-8H,3-6H2;2*1H;;/q;;;;2*+1/p-2/b2*2-1-,8-7-;;;;/r2C8H12.2ClRh/c2*1-2-4-6-8-7-5-3-1;2*1-2/h2*1-2,7-8H,3-6H2;;/b2*2-1-,8-7-;; Key: QSUDXYGZLAJAQU-PXXGERDABU
SMILES Cl1[Rh]Cl[Rh]1.C=1CC\C=C/CCC=1.C/1C\C=C/CC\C=C\1
Properties
Chemical formula	C16H24Cl2Rh2
Molar mass	493.0806 g/mol
Density	1.93 g/cm3
Melting point	243 °C (469 °F; 516 K)
Solubility	dichloromethane
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H315, H317, H319, H335, H411
Precautionary statements	P261, P264, P270, P271, P272, P273, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P312, P321, P330, P332+P313, P333+P313, P337+P313, P362, P363, P391, 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

Preparation and reactions

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]

2 RhCl₃·3H₂O + 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 + nL → [L_nRh(COD)]⁺Cl⁻ (where L = PR₃, alkene, etc. and n = 2 or 3)

In this way, chiral phosphines can be attached to Rh. The resulting chiral complexes are capable of asymmetric hydrogenation.^[3] A related but still more reactive complex is chlorobis(cyclooctene)rhodium dimer. The dimer reacts with a variety of Lewis bases (L) to form adducts with the stoichiometry RhCl(L)(COD).

Structure

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,^[4] in contrast to the highly bent structure of cyclooctadiene iridium chloride dimer where the dihedral angle is 86°.