Cyclooctadiene rhodium chloride dimer
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| Template:Longitem | C16H24Cl2Rh2 |
| Molar mass | 493.0806 g/mol |
| Density | 1.93 g/cm3 |
| Melting point | Template:Chembox CalcTemperatures |
| Solubility | dichloromethane |
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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
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 + Template:MvarL → [LTemplate:MvarRh(COD)]+Cl− (where L = PR3, alkene, etc. and Template:Mvar = 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°.
References
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- ↑ 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. Script error: No such module "CS1 identifiers".
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- ↑ "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. Script error: No such module "CS1 identifiers".
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