Unit 4: Catalysis by Organometallic Compounds
Course Code: CHM-DSC-252
Paper Name: Inorganic Chemistry - III (Organometallic and Analytical Chemistry)
Table of Contents
1. Alkene Hydrogenation (Wilkinson’s Catalyst)
Hydrogenation is the addition of hydrogen to an unsaturated organic compound in the presence of a catalyst.
Wilkinson’s Catalyst
- Formula: RhCl(PPh3)3, which is a coordination complex of Rhodium.
- Type: Homogeneous catalyst (the catalyst and reactants are in the same phase).
- Mechanism:
- Dissociation of a phosphine ligand to create an open coordination site.
- Oxidative addition of dihydrogen (H2) to the metal center.
- Coordination of the alkene to the rhodium.
- Migratory insertion of the hydride into the alkene.
- Reductive elimination of the alkane product.
2. Hydroformylation (Oxo Process)
This process involves the reaction of an alkene with carbon monoxide (CO) and hydrogen (H2) to produce aldehydes.
- Catalyst: Typically uses Cobalt salts (or Rhodium complexes).
- Importance: It is used industrially to produce high-value aldehydes that are converted into alcohols for detergents and plastics.
- Key Step: CO insertion into a metal-alkyl bond to form a metal-acyl intermediate.
3. Synthetic Gasoline (Fischer-Tropsch Reaction)
The Fischer-Tropsch (FT) reaction is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons.
Overall Goal: To produce synthetic fuels (gasoline/diesel) from non-petroleum sources like coal or natural gas.
- Reaction: (2n+1) H2 + n CO → CnH(2n+2) + n H2O.
- Conditions: Typically uses Iron or Cobalt catalysts at high temperatures and pressures.
4. Synthesis Gas by Metal Carbonyl Complexes
Synthesis gas (Syngas) is a mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide.
- Production: Can be generated and manipulated using metal carbonyl complexes.
- Application: Syngas serves as a building block for various chemicals including methanol and ammonia, and acts as the starting material for the Fischer-Tropsch process.
5. Exam Focus: Tips and FAQs
- Wilkinson's Formula: Always remember that RhCl(PPh3)3 is the active precursor for Wilkinson's catalyst.
- Mechanism Keywords: Use terms like "Oxidative Addition," "Migratory Insertion," and "Reductive Elimination" when describing organometallic catalytic cycles.
- Catalyst Metal: Remember that Hydroformylation traditionally uses Cobalt salts, whereas Wilkinson's uses Rhodium.
Frequently Asked Questions
Q: What is the main product of Hydroformylation?
A: Aldehydes are the primary product, which are then often hydrogenated to alcohols.
Q: Why is the Fischer-Tropsch reaction important today?
A: It allows for the production of liquid fuels from alternative sources like coal, biomass, and natural gas, aiding in energy security.
Q: What is a homogeneous catalyst?
A: It is a catalyst that exists in the same physical state (usually liquid solution) as the reactants, like Wilkinson's catalyst in a solvent.