Hexadecacarbonylhexarhodium is a metal carbonyl cluster with the formula Rh₆(CO)₁₆. It exists as purple-brown crystals that are slightly soluble in dichloromethane and chloroform. It is the principal binary carbonyl of rhodium.

Discovery and synthesis

Rh₆(CO)₁₆ was first prepared by Walter Hieber in 1943 by carbonylation of RhCl₃·3H₂O at 80–230 °C and 200 atm

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

with silver or copper as a halide acceptor. Hieber correctly formulated the compound as a binary carbonyl, but suggested the formula Rh₄(CO)₁₁, i.e., CO/Rh ratio of 2.75. The correct formula and structure was subsequently established by Dahl et al. using

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

. The correct CO/Rh ratio is 2.66. Relative to the original preparation, the carbonylation of a mixture of anhydrous rhodium trichloride and

iron pentacarbonyl Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula . Under standard conditions Fe( CO)5 is a free-flowing, straw-colored liquid with a pungent odour. Older samples appear darker. This compound is a common precursor t ...

was shown to give good yields of Rh₆(CO)₁₆. Other compounds of rhodium are also effective precursors such as CO)₂Rh(μ-Cl)sub>2 and rhodium(II) acetate: :3 Rh₂(O₂CCH₃)₄ + 22 CO + 6 H₂O → Rh₆(CO)₁₆ + 6 CO₂ + 12 CH₃COOH :3 CO)₂RhClsub>2 + 4 CO + 6 Cu → Rh₆(CO)₁₆ + 6 CuCl It also arises quantitatively by thermal decomposition of tetrarhodium dodecacarbonyl in boiling hexane: :

Reactions

At least some of the CO ligands can be displaced by donor ligands. Rh₆(CO)₁₆ catalyzes a number of organic reactions including

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or Saturated ...

and

hydroformylation In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes () from alkenes (). This chemical reaction entails the net addition of a formyl group () and a hydrogen ...

References

{{Rhodium compounds Carbonyl complexes Organorhodium compounds Chemical compounds containing metal–metal bonds Rhodium(0) compounds