| Wilkinson's catalyst | |
|---|---|
 |
|
 |
|
 |
|
 |
|
| IUPAC name |
|
| Other names | Rhodium(I) tris- (triphenylphosphine) chloride, Wilkinson’s catalyst, Tris(triphenylphosphine)- rhodium chloride |
| Identifiers | |
| CAS number | [] |
| EC number | |
| RTECS number | none |
| Properties | |
| Molecular formula | C54H45ClP3Rh |
| Molar mass | 925.22 g/mol |
| Appearance | red solid |
| Melting point |
245-250 °C |
| Solubility in water | insoluble in water |
| Solubility in other solvents | benzene |
| Structure | |
| Coordination geometry |
square planar |
| Hazards | |
| R-phrases | none |
| S-phrases | S22 S24/25 |
| 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 references | |
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 popularized its use.
Contents |
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(III) chloride with excess triphenylphosphine. The synthesis is conducted in refluxing ethanol.[1] Triphenylphosphine serves as the reducing agent yielding triphenylphosphine oxide.
- RhCl3(H2O)3 + 4 PPh3 → RhCl(PPh3)3 + O=PPh3 + 2 HCl + 2 H2O
Catalytic applications
Wilkinson's catalyst catalyzes the hydrogenation of alkenes,[2][3] 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 (olefin insertion), and reductive elimination results in extrusion of the alkane product, e.g.:
Other applications of Wilkinson’s catalyst includes the catalytic hydroboration of alkenes with catecholborane and pinacolborane,[4] and the selective 1,4-reduction of α, β-unsaturated carbonyl compounds in concert with triethylsilane.[5] When the triphenylphosphine ligands are replaced by chiral phosphines (e.g., chiraphos, DIPAMP, DIOP), the catalyst becomes chiral and convert prochiral alkenes into enantiomerically enriched alkanes via the process called asymmetric hydrogenation.[6]
Other reactions of RhCl(PPh3)3
RhCl(PPh3)3 reacts with CO to give RhCl(CO)(PPh3)2, which is structurally analogous to Vaska's complex but much less reactive. The same complex arises from the decarbonylation of aldehydes, although the reaction is stoichiometric:
- RhCl(PPh3)3 + RCHO → RhCl(CO)(PPh3)2 + RH + PPh3
Upon stirring in benzene solution, RhCl(PPh3)3 converts to the poorly soluble red-colored species Rh2Cl2(PPh3)4. This conversion further demonstrates the lability of the triphenylphosphine ligands.
References
- ^ Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. (1966). "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: 1711–1732. doi:.
- ^ A. J. Birch, D. H. Williamson (1976). Organic Reactions 24: 1ff.
- ^ B.R. James, Homogeneous Hydrogenation. John Wiley & Sons, New York, 1973.
- ^ D. A. Evans, G. C. Fu and A. H. Hoveyda (1988). "Rhodium(I)-catalyzed hydroboration of olefins. The documentation of regio- and stereochemical control in cyclic and acyclic systems". J. Am. Chem. Soc. 110 (20): 6917–6918. doi:.
- ^ I. Ojima, T. Kogure, Y. Nagai (1972). "Selective reduction of α,β-unsaturated terpene carbonyl compounds using hydrosilane-rhodium(I) complex combinations". Tetrahedron Lett. 13 (49): 5035–5038. doi:.
- ^ W. S. Knowles (2003). "Asymmetric Hydrogenations (Nobel Lecture 2001)". Advanced Synthesis and Catalysis 345: 3–13. doi:.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
