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Wilkinson's catalyst is a rhodium coordinate compound. It allows the reaction to go forward more quickly. It's used in the unsaturated organic compound hydrogenation process. The coordination chemical Wilkinson's Catalyst [IUPAC Name: chloridotris(triphenylphosphine)rhodium(I)] has rhodium as its coordination center. It's widely utilized in the hydrogenation of alkenes as a catalyst. Wilkinson's catalyst has the chemical formula [RhCl(PPh3)3], where 'Ph' denotes a phenyl group. This coordination complex is a reddish-brown solid at room temperature. Wilkinson's catalyst is named after Sir Geoffrey Wilkinson, an English scientist. Wilkinson's Catalyst employs a square planar structure, as determined by single-crystal X-ray diffraction examinations (slightly distorted). In this molecule, the rhodium center is linked to four ligands.
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Key Terms: Coordinate Compound, Hydrogenation, Alkenes, Alkanes, Alkynes, Catalyst, Phenyl, Ligands, X-ray Diffraction
Properties of Wilkinson’s Catalyst
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The physical and chemical properties are mentioned below.
Physical Properties of Wilkinson Catalyst
- The Wilkinson catalyst is a solid-state catalyst.
- Wilkinson catalyst is a reddish-brown color.
- The Wilkinson catalyst is soluble in nonpolar chemicals including benzene, dichloromethane, and tetrahydrofuran but not in polar molecules like water.
- Wilkinson catalyst has a molecular mass of 925.22 grams/mole.
- The Wilkinson catalyst has a melting point of roughly 520 K.
Chemical Properties of Wilkinson Catalyst
- The Wilkinson catalyst has a dsp2 hybridization and a square planner form.
- As a result of the reaction between the Wilkinson catalyst RhCl(PP3)3 and carbon monoxide, the product is bis (triphenylphosphine) rhodium carbonyl chloride RhCl(CO)(PPh3)2. The reaction with aldehydes might also result in the formation of this resultant molecule.
RhCl(PPh3)3 + RCHO → RhCl(CO)(PPh3)2 + RH + PPh3
- When Wilkinson catalysts are combined with benzene, they can form a dimer. This newly produced dimer [RhCl(PPh3)3 is insoluble and colourless.
- By reacting the Wilkinson catalyst with alkali, hydrogen, and excess triphenylphosphine, it may be transformed into the hydridotetrakis (triphenylphosphine) rhodium (I) HRh (PPh3)4.
RhCl(PP3)3 + H2 + base → HRh (PPh3)4
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Preparation of Wilkinson’s Catalyst
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In the presence of ethanol, hydrated rhodium(III) chloride can be combined with excess triphenylphosphine to make Wilkinson's catalyst (which acts as a refluxing agent). The triphenylphosphine (chemical formula P(C6H5)3) works as a reducing agent, capable of oxidizing itself from a +3 to a +5 oxidation state.
One equivalent of triphenylphosphine converts rhodium(III) to rhodium(I) during the manufacture of Wilkinson's catalyst, whereas three additional equivalents bind to the metal as ligands in the end product.
4P(C6H5)3 + RhCl3(H2O)3 → RhCl(P(C6H5)3)3 + OP(C6H5)3 + 2HCl + 2H2O
Mechanism of Catalysis for the Hydrogenation of Alkenes
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- The dissociation of one or two triphenylphosphine ligands produces a 14-electron or 12-electron complex.
- The oxidative addition of molecular hydrogen (H2) to Wilkinson's catalyst's metal core (rhodium) now takes place.
- The production of a pi complex with the alkene is the mechanism's third stage.
- The hydrogen is introduced into the complex by migratory insertion, which can take place via intramolecular hydride transfer or olefin insertion.
- Finally, the pi complex undergoes reductive elimination to renew the catalyst and provide the necessary alkene product.
Mechanism of Catalyst
The mechanism of action of Wilkinson's catalyst for the hydrogenation of olefins is illustrated in the diagram above.
Application of Wilkinson Catalyst
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- For the hydrogenation process of unsaturated hydrocarbons, the Wilkinson catalyst is commonly utilized (olefins). It introduces molecular hydrogen into the molecule at an unsaturated carbon site.
- In the addition of a hydrogen-acyl group to alkenes, the Wilkinson catalyst can be utilized.
- It is very important in the alkene hydroboration process.
- In the selective hydrogenation of alkenes, the Wilkinson catalyst is utilized. It prefers to add hydrogen to the unsaturated carbon position that is least inhibited.
- In the presence of hydrogen and a strong base, functionalized tri-substituted alkenes and internal alkynes can be hydrogenated using Wilkinson's catalyst. A highly reactive Rh(I) species with considerably higher catalytic activity is produced in this case.
Structure of Wilkinson’s Catalyst
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Rhodium has four complexes in Wilkinson's catalyst that allow it to decrease the double bond and generate a complex. Because of its huge size, the molecule can reduce the least hindered double bond. Even though there are several double bonds on the molecule, Wilkinson's catalyst will only decrease the least hindered double bond since that is where the catalyst can fit.
Structure of Wilkinson’s Catalyst
Things to Remember
- Wilkinson catalyst is named after Nobel Laureate and scientist Sir Geoffrey Wilkinson. He was the one who popularised it.
- Rhodium has an oxidation state of +4 to -3. The oxidation state of rhodium in the Wilkinson catalyst is +1.
- Wilkinson catalysts are capable of breaking down double bonds or alkenes. It's a solid that's red-brown in hue.
- In hydrocarbon solvents such as dichloromethane, tetrahydrofuran, and benzene, the Wilkinson catalyst is soluble. In the halogenation of alkenes, this is a commonly utilized compound.
- It is effective in the reduction of a specific double bond in a molecule because it selectively reduces double bonds or alkenes.
- When the chemical is mixed into a benzene solution, it dimerizes.
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Sample Questions
Ques. Why is the Wilkinson catalyst an organometallic compound? (2 Marks)
Ans. It's an organometallic compound that's commonly utilized for halogenating alkenes and forms an Rh-C bond in the process. The chemistry of metal-carbon bonding is known as organometallic chemistry. Wilkinson catalyst's chemical formula reveals that it comprises carbon as well as the metal rhodium. As a result, it's a metal organ complex.
Ques. How does a catalyst work? (2 Marks)
Ans. In most cases, catalysts function as direct intermediates between their substrates and the chemical process. The catalysts are regenerated to their original condition at the end of a reaction, resulting in no net change, allowing them to participate in a new reaction. Catalysts are well-known for speeding up chemical reactions so that a large quantity of product may be obtained in a short amount of time.
Ques. What are a few examples of catalysts? (2 Marks)
Ans. Catalysts include zinc oxide, which is used in the reaction between sulphur and natural rubber, concentrated sulphuric acid, which is used in the esterification of carboxylic acid and alcohol, and phosphoric acid, which is used to hydrate alkenes.
Ques. What does Wilkinson's catalyst do? (2 Marks)
Ans. For the hydrogenation process of unsaturated hydrocarbons, the Wilkinson catalyst is commonly utilized (olefins). It introduces molecular hydrogen into the molecule at an unsaturated carbon site. In the addition of a hydrogen-acyl group to alkenes, the Wilkinson catalyst can be utilized.
Ques. What allows Wilkinson's catalyst to reduce alkenes? (2 Marks)
Ans. [Rh(Ph3P)3] Wilkinson's Catalyst Alkenes are hydrogenated with the help of Cl. Rhodium may create a 6-coordinate complex, allowing it to reduce alkenes selectively. Wilkinson's catalyst cannot decrease carbon-oxygen double bonds or double bonds in general, but it can reduce the least hindered double bond selectively.
Ques. What are everyday examples of catalysts? (2 Marks)
Ans. Catalysts are used in almost every aspect of your everyday life, including automobiles, Post-It notes, laundry detergent, and beer. Bread, cheddar cheese, and roast turkey are all components of your sandwich. Catalysts aid in the breakdown of paper pulp, resulting in the smooth paper used in your magazine. Every night, they clean your contact lenses.
Ques. Is Wilkinson catalyst heterogeneous? (2 Marks)
Ans. In general, homogeneous catalysts are all the same, whereas heterogeneous catalysts are made up of several different elements. In chemistry, the same is true. Homogeneous mixes have the same consistency throughout. Wilkinson's catalyst is RhCl(PPh3)3 - Chlorotris(triphenylphosphine)rhodium(I). It is used as a catalyst for homogenous hydrogenation. It's a 16-electron diamagnetic square planar complex.
Ques. What is the hybridization of the Wilkinson catalyst? (2 Marks)
Ans. Wilkinson's catalyst is known by the IUPAC name chloridotris(triphenylphosphine)rhodium (I). The core metal atom is Rhodium, a transition metal ion with a coordination number of four and an sp2 hybridization. The geometry of the complex is square planar because it has an sp2 hybridization.
Ques. What is the most common catalyst? (2 Marks)
Ans. The high-temperature shift (HTS) and low-temperature shift (LTS) catalysts are the most frequent catalysts employed in the water-gas shift process. Iron oxide stabilized by chromium oxide is used in the HTS catalyst, while copper is used in the LTS catalyst. Platinum and nickel are good catalysts because they adsorb firmly enough to retain and activate the reactants while yet allowing the products to escape.
Ques. How does MN act as a catalyst? (2 Marks)
Ans. When manganese oxide is heated to above 1000 degrees Celsius in the air, Mn3O4 is created. To make nano-crystalline Mn3O4 and different syntheses that convert MnII to MnVI reduction. Mn3O4 has been used as a catalyst in a variety of processes, including the oxidation of CH4 and CO, as well as catalytic burning of organic molecules.
Ques. Are catalysts affected by temperature and pH? (2 Marks)
Ans. Raising the temperature of a reaction speeds it faster, whereas reducing the temperature slows it down. Extremely high temperatures, on the other hand, can cause an enzyme to lose its form (denature) and stop functioning. Each enzyme has a specific pH range that it favors. Enzyme activity will be slowed if the pH is changed outside of this range. Since side reactions including WGS and the synthesis of formate from CO2 were observed, the pH of the catalytic solution was shown to alter both the activity and selectivity of the AFTS reaction.
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