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Wilkinson's catalyst



Wilkinson's catalyst
IUPAC name Chlorotris(triphenylphosphine)-
rhodium
Other names Rhodium(I) tris-
(triphenylphosphine) chloride,
Wilkinson’s catalyst,
Tris(triphenylphosphine)-
rhodium chloride
Identifiers
CAS number 14694-95-2
EINECS number 238-744-5
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
Solubility in other solvents benzene
Structure
Coordination
geometry
square planar
Hazards
Main hazards none
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 disclaimer and 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 popularlized its use.

Additional recommended knowledge

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 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

Catalytic applications

Wilkinson's catalyst 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

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.

References

  1. ^ 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:10.1039/J19660001711.
  1. (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.
  2. 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:10.1021/ja00228a068.
  3. I. Ojima, T. Kogure, Y. Nagai, Tetrahedron Lett. 1972, page 5035.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Wilkinson's_catalyst". A list of authors is available in Wikipedia.
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