Wilkinson's catalyst

Chembox new
ImageFile = Wilkinson's-catalyst-2D.png ImageSize = 200px
ImageName = Wilkinson's catalyst
ImageFile1 = Wilkinson's-catalyst-no-hydrogens-3D-balls.png ImageSize1 = 120px
ImageName1 = Wilkinson's catalyst
ImageFile2 = Wilkinson's-catalyst-3D-vdW.png ImageSize2 = 120px
ImageName2 = Wilkinson's catalyst
IUPACName = ("SP"-4)chloridotris(triphenylphosphane)
rhodium
OtherNames = Rhodium(I) tris-
(triphenylphosphine) chloride,
Wilkinson’s catalyst,
Tris(triphenylphosphine)-
rhodium chloride
Section1 = Chembox Identifiers
SMILES =
EINECS = 238-744-5
CASNo = 14694-95-2
RTECS = none
Section2 = Chembox Properties
Formula = C₅₄H₄₅ClP₃Rh
MolarMass = 925.22 g/mol
Appearance = red solid
Density =
Solubility = insoluble
Solvent = other solvents
SolubleOther = benzene
MeltingPt = 245-250 °C
BoilingPt =
Section3 = Chembox Structure
Coordination = square planar
CrystalStruct =
Dipole =
Section7 = Chembox Hazards
ExternalMSDS =
MainHazards = none
RPhrases = none
SPhrases = S22 S24/25
Section8 = Chembox Related
OtherCpds = triphenylphosphine
Pd(PPh₃)₄
[Vaska's complex|IrCl(CO) [P(C₆H₅)₃] ₂]

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.

tructure 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 triphenylphosphine. The synthesis is conducted in refluxing ethanol. [cite journal|author=Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G.| title=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= Journal of the Chemical Society A | date = 1966 | pages = 1711–1732 | doi = 10.1039/J19660001711] 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, [cite journal | author = A. J. Birch, D. H. Williamson | journal = Organic Reactions | year = 1976 | volume = 24 | pages = 1ff] [B.R. James, "Homogeneous Hydrogenation". John Wiley & Sons, New York, 1973.] 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, [cite journal | author = D. A. Evans, G. C. Fu and A. H. Hoveyda | title = Rhodium(I)-catalyzed hydroboration of olefins. The documentation of regio- and stereochemical control in cyclic and acyclic systems | year = 1988 | journal = J. Am. Chem. Soc. | volume = 110 | issue = 20 | pages = 6917–6918 | doi=10.1021/ja00228a068] and the selective 1,4-reduction of α, β-unsaturated carbonyl compounds in concert with triethylsilane. [cite journal | author = I. Ojima, T. Kogure, Y. Nagai | journal = Tetrahedron Lett. | year = 1972 | volume = 13 | issue = 49 | pages = 5035–5038 | doi = 10.1016/S0040-4039(01)85162-5 | title = Selective reduction of α,β-unsaturated terpene carbonyl compounds using hydrosilane-rhodium(I) complex combinations] When the triphenylphosphine ligands are replaced by chiralphosphines (e.g., chiraphos, DIPAMP, DIOP), the catalyst becomes chiral and convert prochiral alkenes into enantiomerically enriched alkanes via the process called asymmetric hydrogenation. [cite journal | author = W. S. Knowles | title = Asymmetric Hydrogenations (Nobel Lecture 2001) | journal = Advanced Synthesis and Catalysis | year = 2003 | volume = 345 | pages = 3–13 | doi = 10.1002/adsc.200390028 ]

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