Wilkinson's catalyst, also known as chloridotris(triphenylphosphane)rhodium(I), is a coordination complex of rhodium with the formula RhCl(PPh3)3. It is a red-brown solid that is soluble in hydrocarbon solvents and used widely as a catalyst for hydrogenation of alkenes. Wilkinson's catalyst is obtained by treating rhodium(III) chloride hydrate with excess triphenylphosphine, which acts as a reducing agent to reduce rhodium from Rh(III) to Rh(I). It adopts a slightly distorted square planar structure and undergoes fast dynamic exchange processes in solution.

1. Wilkinson’s Reagent
SHIKHA D. POPALI
HARSHPAL SINGH WAHI
Department of Pharmaeutical chemistry M.pharm 1St yr
GURUNANAKCOLLEGEOF PHARMACY,NAGPUR

2. • Wilkinson's catalyst, is the common name for chloridotris(triphenylphosphane)rhodium(I), a cordination
complex of rhodium with the formula RhCl(PPh3)3(Ph = phenyl).
• It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so
in tetrahydrofuran or chlorinated solvents such as dichloromethane.
• The compound is widely used as a catalyst for hydrogenation of alkenes.
Introduction:
tris(triphenylphosphine)chlorhodium
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3. Structure and basic properties
 According to single crystal X-ray diffraction the compound adopts a slightly distorted square
planar structure.
 In analyzing the bonding, it is a complex of Rh(I), a d8 transition metal ion. From the
perspective of the 18-electron rule, the four ligands each provides two electrons, for a total of
16-electrons.
 As such the compound is coordinatively unsaturated. Furthermore, in solution the complex
undergoes fast dynamic exchange processes both intermolecular (one of the PPh3 is labile and
is constantly exchanged between the inner coordination Rh sphere and the solution, although
this fast equilibrium is really balanced towards the starting triphosphine complex, K = 10−5 M)
and intramolecular (fluxionality).
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4. Wilkinson's catalyst is usually obtained by treating rhodium(III) chloride hydrate with an excess
of triphenylphosphine in refluxing ethanol. Triphenylphosphine serves as a two-electron reducing agent that oxidizes
itself from oxidation state (III) to (V). In the synthesis, three equivalents of triphenylphosphine become ligands in the
product, while the fourth reduces rhodium(III) to rhodium(I).
RhCl3(H2O)3 + 4 PPh3 → RhCl(PPh3)3 + OPPh3 + 2 HCl + 2 H2O
Catalytic applications
1. Decarbonylation of Aldehyde
This reaction is of value when a carbonyl group is needed foe activation in a step in a synthetic sequence and has to be
removed subsequently. Decarbonylation wih Wilkinson’s catalyst goes through complexes of the type is an intramolecular
reaction and gives a retention of configuration at a chiral R.
Synthesis
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5. Decarbonylation of an aldehyde with Wilkinson’s catalyst 5

6. 2. Formation of Carbon-carbon bonds
In the example, the first step involves a ligand exchange by a combination of ligand association-dissociation step and a
methyl group is inserted into the coordination sphere of rhodium. An oxidative addition then incorporates the phenyl
group into the rhodium coordination sphere and subsequent reductive elimination then joins methyl group and the
benzene ring to yield toluene in the last step.
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7. 3. Hydrogenation of alkenes using Wilkinson’s catalyst
The mechanism of this reaction 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, migratory insertion (intramolecular hydride transfer or olefin insertion), and reductive
elimination complete the formation of the alkane product.
Mechanism of hydrogenation with Wilkinson’s catalyst
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8. THANK YOU
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