Rhodium carbonyl chloride
Chemical compound
From Wikipedia, the free encyclopedia
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.
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| Names | |
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| IUPAC name
Di-μ-chloro-tetracarbonyldirhodium(I) | |
Other names
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| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.035.021 |
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PubChem CID |
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| Properties | |
| C4O4Cl2Rh2 | |
| Molar mass | 388.76 |
| Appearance | red brown volatile solid |
| Density | 2.708 g/cm3 |
| Melting point | 120–125 °C (248–257 °F; 393–398 K) |
| Hazards | |
| GHS labelling:[1] | |
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| Danger | |
| H301, H302, H330 | |
| P260, P264, P270, P271, P284, P301+P316, P301+P317, P304+P340, P316, P320, P321, P330, P403+P233, P405, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 126.8° between the two RhCl2 planes. The metals are nonbonding.[2]
Synthesis and reactions
First prepared by Walter Hieber,[3] 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.[4]
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).
The dimer reacts with a variety of Lewis bases (:B) to form adducts RhCl(CO)2:B. Its reaction with tetrahydrothiophene and the corresponding enthalpy are:
- 1/2 Rh2Cl2(CO)4 + :S(CH2)4 → RhCl(CO)2:S(CH2)4 ΔH = -31.8 kJ mol−1
This enthalpy corresponds to the enthalpy change for a reaction forming one mole of the product, RhCl(CO)2:S(CH2)4, from the acid dimer. The dissociation energy for rhodium(I) dicarbonyl chloride dimer, which is an energy contribution prior to reaction with the donor,
- Rh2Cl2(CO)4 → 2 RhCl(CO)2
has been determined by the ECW model to be 87.1 kJ mol−1
N-heterocyclic carbene (NHC) ligands react with rhodium carbonyl chloride to give monomeric cis-[RhCl(NHC)(CO)2] complexes. The IR spectra of these complexes have been used to estimate the donor strength of NHCs.[5][6]