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.
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[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 The 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 When the triphenylphosphine ligands are replaced by chiral phosphines (e.g. Chiraphos, DIPAMP, DIOP), the catalyst becomes chiral and is capable of making chiral alkanes from prochiral alkenes through asymmetric hydrogenation.5
[edit] 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
- J. A. Osborn, F. H. Jardine, J. F. Young, G. Wilkinson, Journal of the Chemical Society A. 1966, pages 1711ff.
- (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.
- W. S. Knowles, Adv. Synthesis and Catalysis 2003, volume 345(1&2), pages 3-13.
