Wilkinson's catalyst
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| Wilkinson's catalyst | |
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| General | |
| Systematic name | Chlorotris(triphenylphosphine)- rhodium |
| Other names | Rhodium(I) tris- (triphenylphosphine) chloride, Wilkinson’s catalyst, Tris(triphenylphosphine)- rhodium chloride |
| Molecular formula | C54H45ClP3Rh |
| SMILES | ? |
| Molar mass | 925.22 g/mol |
| EINECS number | 238-744-5 |
| Appearance | red solid |
| CAS number | [14694-95-2] [1] |
| Properties | |
| Density and phase | ? g/cm3 |
| Solubility in water | insoluble |
| Other solvents | benzene |
| Melting point | 245-250 °C |
| Boiling point | ? °C (? K) |
| Structure | |
| Coordination geometry |
square planar |
| Crystal structure | ? |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | none |
| NFPA 704 | |
| R/S statement | R: none S: 22-24/25 |
| RTECS number | none |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related compounds | triphenylphosphine Pd(PPh3)4 IrCl(CO)[P(C6H5)3]2 |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Wilkinson's catalyst is the common name for chlorotris(triphenylphosphine)rhodium(I), a chemical compound with the formula RhCl(PPh3)3 (Ph = phenyl). It is named after the late organometallic chemist and 1973 Nobel Laureate, Sir Geoffrey Wilkinson who popularlized its use.
Contents |
[edit] Structure and basic properties
The compound is a square planar, 16-electron complex and is usually isolated in the form of a red-violet crystalline solid from the reaction of rhodium trichloride with triphenylphosphine. The synthesis is conducted in refluxing ethanol.[1]Ethanol serves as the reducing agent.
- RhCl3(H2O)3 + CH3CH2OH + 3 PPh3 → RhCl(PPh3)3 + CH3CHO + 2 HCl + 3 H2O
The PPh3 probably serves as a base to absorb the HCl.
[edit] Catalytic applications
Wilkinson's catalyst is catalyzes the hydrogenation of alkenes,2 the mechanism of which involves the initial dissociation of one or two triphenylphosphine ligands to give 14 or 12-electron complexes, respectively, followed by oxidative addition of H2 to the metal. Subsequent π-complexation of alkene, intramolecular hydride transfer, and reductive elimination results in extrusion of the alkane product, e.g.:
Other applications of Wilkinson’s catalyst include: catalytic hydroboration of alkenes using catecholborane and pinacolborane,3 and the selective 1,4-reduction of α, β-unsaturated carbonyl compounds in concert with triethylsilane.4
[edit] Other reactions of RhCl(PPh3)3
RhCl(Ph3P)3 reacts with CO to give RhCl(CO)(PPh3)2, which is structurally analogous to Vaska's complex. The complex will also decarbonylate aldehydes, although the reaction is stoiochiometric:
- RhCl(PPh3)3 + RCHO → RhCl(CO)(PPh3)2 + RH + PPh3
Upon stirring in benzene solution, RhCl(PPh3)3 loses PPh3 to give the poorly soluble red-colored species Rh2Cl2(PPh3)4. This conversion demonstrates the lability of the triphenylphosphine ligands.
[edit] References
- ^ Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. "The Preparation and Properties of Tris(triphenylphosphine)halogenorhodium(I) and Some Reactions Thereof Including Catalytic Homogeneous Hydrogenation of Olefins and Acetylenes and Their Derivatives" Journal of the Chemical Society A, 1966, pages 1711 - 1732, DOI: 10.1039/J19660001711.
- (a) A. J. Birch, D. H. Williamson, Organic Reactions 1976, volume 24, page 1ff; (b) B.R. James, Homogeneous Hydrogenation. John Wiley & Sons, New York, 1973.
- D. A. Evans, G. C. Fu, and A. H. Hoveyda, Journal of the American Chemical Society 1988, volume 110, page 6917.
- I. Ojima, T. Kogure, Y. Nagai, Tetrahedron Lett. 1972, page 5035.
