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. .

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:
 * 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  →  [LnRh(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.