Wilkinson's catalyst, chlorotris(triphenylphosphine)rhodium(I), is an organometallic catalyst that is very effective for the homogeneous hydrogenation of unsaturated compounds at room temperature and atmospheric pressure. Its mechanism involves five steps - ligand dissociation, oxidative addition of hydrogen, alkene coordination, migratory insertion, and reductive elimination - known as Tolman's catalytic cycle. This cycle allows the catalyst intermediates to shuttle between 18 and 16 electron configurations, making the electron shifts energetically favored.

1. Organometallic Catalysts – Part I
• Mechanism of Wilkinson’s Catalyst

2. Organometallic catalysts
• In chemistry, homogeneous catalysis is
catalysis in a solution by a soluble catalyst.
• Homogeneous catalysis refers to catalytic
reactions where the catalyst is in the same
phase as the reactants.
• The term is used almost exclusively to
describe solutions and often implies catalysis
by organometallic compounds.

3. • Polymer industry
• Pharma industry
• Petroleum industry
• Organic synthesis

4. Wilkinson's catalyst
• Chlorotris(triphenylphosphine)rhodium(I),
[RhCl(PPh3)3]
•
• Discovered accidentally by Fred Jardine,(PhD scholor) working for Geoffrey
Wilkinson was trying to make [RhCl3(PPh3)3], from the reaction of hydrated
rhodium trichloride and excess triphenylphosphine in boiling ethanol.
[RhCl3(H2O)3] + 4 PPh3 [RhCl(PPh3)3] + Ph3PO + 2 HCl + 2
H2O

5. Hydrogenation of alkenes
It is a very active catalyst for the rapid homogenous hydrogenation
(i.e. in solution) of unsaturated compounds.
working rapidly at 25°C and 1 atm pressure of hydrogen gas

6. mechanism
• Mechanism involves 5 steps
• Step (i) Dissociation of one ligand
• One of the Ligand is lost replaced by the
solvent S

7. • Step (ii) Oxidative addition of Hydrogen
• Hydrogen is added to the metal leading to the increase in both
oxidation number and coordination number.
• Step (iii) Co-ordination of alkene

8. • Step (iv) Migratory insertion
• One hydrogen migrates and inserted between carbon
and hydrogen of alkene
• Step (v) Reductive elimination
• Release of the product with regeneration of the
catalyst

9. Tolman’s catalytic cycle
• Hydrogenation of alkenes by Wilkinson’s catalyst is
called as Tolman’s catalytic cycle or loop.
• It is an extended version of 18e-
rule.
• In reactions catalyzed by homogeneous
organometallic catalysts, the intermediates
obtained in different steps shuttle between 18 and
16e-
.
• The shifting of electrons are energetically favored
hence allowed.

10. Hydrgenation of alkenes by Wilkinson’s
catalyst

11. References
http://www.chm.bris.ac.uk/motm/wilcat/wilcath.htm
https://nptel.ac.in/courses/103103026/pdf/mod3.pdf
https://en.wikipedia.org/wiki/Homogeneous_catalysis
https://www.adichemistry.com/inorganic/organometallic/catalysis/
wilkinson/wilkinsons-catalyst.html
Concise Coordination Chemistry Gopalan R. & Ramalingam V.
Vikas Publishing House Pvt Limited, 2001
Inorganic Chemistry: Principles of Structure and Reactivity
James E. Huheey, Ellen A. Keiter, Richard L. Keiter, Okhil K.
Medhi Pearson Education India, 2006 - Chemistry, Inorganic
Kinetics of Multistep Reactions Friedrich G. Helfferich
Elsevier, 15-Sep-2004. Pg. 200.