Rhodium carbonyl chloride

Rhodium carbonyl chloride

Identifiers
CAS Number	14523-22-9
ECHA InfoCard	100.035.021
Properties
Chemical formula	C4O4Cl2Rh2
Molar mass	388.76
Appearance	red brown volatile solid
Density	2.708 g/cm−3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Rhodium carbonyl chloride is an organorhodium compound with the formula Rh₂Cl₂(CO)₄. It is a red-brown volatile solid that is soluble in nonpolar organic solvents. It is a precursor to other rhodium carbonyl complexes, some of which are useful in homogeneous catalysis.

Structure

The molecule consists of two planar Rh(I) centers linked by two bridging chloride ligands and four CO ligands. X-ray crystallography shows that the two Rh(I) centers are square planar with the dihedral angle of 53° between the two RhCl₂ planes. The metals are nonbonding.

Synthesis and reactions

First prepared by Walter Hieber, it is typically prepared by treating hydrated rhodium trichloride with flowing carbon monoxide, according to this idealized redox equation:

2 RhCl₃(H₂O)₃ + 6 CO → Rh₂Cl₂(CO)₄ + 2 COCl₂ + 6 H₂O.

The complex reacts with triphenylphosphine to give the bis(triphenylphosphine)rhodium carbonyl chloride:

Rh₂Cl₂(CO)₄ + 4 PPh₃ → 2 trans-RhCl(CO)(PPh₃)₂ + 2 CO

With chloride salts, the dichloride anion forms:

Rh₂Cl₂(CO)₄ + 2 Cl⁻ → 2 cis-[RhCl₂(CO)₂]⁻

With acetylacetone, rhodium carbonyl chloride reacts to give dicarbonyl(acetylacetonato)rhodium(I).