Cyclooctadiene rhodium chloride dimer is the organorhodium compound with the formula Rh₂Cl₂(C₈H₁₂)₂, commonly abbreviated hCl(COD)sub>2 or Rh₂Cl₂(COD)₂. This yellow-orange, air-stable compound is a widely used precursor to homogeneous catalysts.Giordano, G.; Crabtree, R. H. "Di-μ-chloro-bis(η⁴-1,5-cyclooctadiene)dirhodium(I)" Inorganic Syntheses, 1990, volume 28, pages 88-90.

Preparation and reactions

The synthesis of hCl(COD)sub>2 involves heating a solution of hydrated

rhodium trichloride Rhodium is a chemical element; it has symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring isoto ...

with

1,5-cyclooctadiene 1,5-Cyclooctadiene (also known as cycloocta-1,5-diene) is a cyclic compound, cyclic hydrocarbon with the chemical formula , specifically . There are three configurational isomers with this structure, that differ by the arrangement of the four C� ...

in aqueous

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

in the presence of

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

: :2 RhCl₃·3H₂O + 2 COD + 2 CH₃CH₂OH + 2 Na₂CO₃ → hCl(COD)sub>2 + 2 CH₃CHO + 8 H₂O + 2 CO₂ + 4 NaCl hCl(COD)sub>2 is principally used as a source of the

electrophile In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an ...

" h(COD)sup>+." : hCl(COD)sub>2 + L → Rh(COD)sup>+Cl⁻ (where L = PR₃, alkene, etc. and = 2 or 3) In this way,

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

phosphines Organophosphines are organophosphorus compounds with the formula PR''n''H3−''n'', where R is an organic substituent. These compounds can be classified according to the value of ''n'': primary phosphines (''n'' = 1), secondary phosphine ...

can be attached to Rh. The resulting chiral complexes are capable of

asymmetric hydrogenation Asymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from oth ...

. 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

and two chloride ligands that are shared between the Rh centers. The Rh₂Cl₂ core is also approximately planar,"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. in contrast to the highly bent structure of cyclooctadiene iridium chloride dimer where the dihedral angle is 86°.

References

External links

* {{Rhodium compounds Organorhodium compounds Homogeneous catalysis Cyclooctadiene complexes Dimers (chemistry) Chloro complexes Rhodium(I) compounds