Wilkinson Catalyst

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What is Wilkinson Catalyst?

Wilkinson’s catalyst is a coordinate compound of rhodium. It enables the reaction to proceed in a faster manner. It is used in the hydrogenation reaction of the unsaturated organic compound. In this article, we have covered the IUPAC name of Wilkinson catalyst, its uses, its structure, and mechanism.

Wilkinson Catalyst Formula

The Wilkinson catalyst formula is [RhCl(PPh3)3]. Wilkinson Catalyst Formula represents the coordinate compound of rhodium. Its formula is made up of one rhodium, one chloride, and three PPh3 units.

IUPAC Name of Wilkinson Catalyst

The IUPAC name of the Wilkinson catalyst is Chloridotris (triphenylphosphine) rhodium(I)].

Wilkinson's Catalyst Structure

In Wilkinson’s catalyst structure the rhodium is bonded with three triphenylphosphine units by three single covalent bonds and one chlorine element is bonded with rhodium by a single covalent bond. Wilkinson catalyst hybridisation is dsp2. The dsp2 hybridisation represents the square planer shape. It is an inner complex molecule because the orbital involved in this compound is inner 3d.

Properties of Wilkinson Catalyst

Physical Properties of Wilkinson Catalyst

  • Wilkinson catalyst exists in the solid-state.

  • Wilkinson catalyst is red-brown.

  • Wilkinson catalyst is not soluble in polar compounds such as water and it is soluble in nonpolar compounds such as benzene, dichloromethane, and tetrahydrofuran.

  • The molecular mass of the Wilkinson catalyst is 925.22 grams/mole.

  • The melting point of the Wilkinson catalyst is around 520 K.

Chemical Properties of Wilkinson Catalyst

The chemical properties shown by the Wilkinson catalyst is the result of the electronic configuration and the shape attained by the catalyst.

  • The hybridisation of Wilkinson catalyst is dsp2 and its shape is a square planner.

  • Wilkinson catalyst RhCl(PP3)3 reacts with the carbon monoxide and forms bis (triphenylphosphine) rhodium carbonyl chloride RhCl(CO)(PPh3)2 as a product. This formed product compound can also be formed by the reaction with the aldehydes.

RhCl(PPh3)3 + RCHO → RhCl(CO)(PPh3)2 + RH + PPh3

  • Wilkinson catalyst can form a dimer when mixed in the benzene solution. This formed dimer [RhCl(PPh3)3 is poorly soluble and red.

  • Wilkinson catalyst can be converted into the hydridotetrakis (triphenylphosphine) rhodium (I) HRh (PPh3)4 on reacting it with the alkali, hydrogen and excess triphenylphosphine.

RhCl(PP3)3 + H2 + base → HRh (PPh3)4

Wilkinson Catalyst Uses

  • Wilkinson catalyst is widely used for the hydrogenation reaction of unsaturated hydrocarbons (olefins). It adds the molecular hydrogen at an unsaturated carbon position in the compounds.

  • Wilkinson catalyst can be used in the addition of hydrogen-acyl group to the alkenes.

  • It plays a major role in the hydroboration reaction of the alkenes.

  • Wilkinson catalyst is used in the selective hydrogenation of the alkenes. It preferably adds the hydrogen at the least hindered unsaturated carbon position.

Catalytic Hydrogenation of Alkenes

Wilkinson catalyst is widely used in the hydrogenation process. It adds the molecular hydrogen t the unsaturated carbon in the compound. It preferably adds the hydrogen at the less hindered carbon.

Catalytic Hydrogenation Mechanism

  • The first step involved in the hydrogenation mechanism is the dissociation of the triphenylphosphine ligands, which results in the formation of a 14 or 12 electron complex.

  • Then it undergoes oxidative hydrogenation.

  • The pi complex with the alkene is formed.

  • Migratory insertion and reductive elimination complete the alkane formation step.

Preparation of the Wilkinson Catalyst

Wilkinson catalyst can be prepared from the hydrated form of rhodium(III) chloride. Rhodium (III) chloride undergoes the reaction with excess triphenylphosphine with ethanol. Here, ethanol acts as a refluxing agent. Triphenylphosphine is a good reducing agent and represented as P(C6H5)3. In the preparation reaction of the Wilkinson, catalyst triphenylphosphine reacts with the rhodium chloride and reduces it from the +3 oxidation state to the +1 oxidation state.

4P(C6H5)3 + RhCl3(H2O)3 → RhCl(P(C6H5)3)3 + OP(C6H5)3 + 2HCl + 2H2O

Did You Know?

  • Wilkinson catalyst represents the name of chemist and Nobel laureate Sir Geoffrey Wilkinson. He first popularizes its use.

  • The range of oxidation state of rhodium is +4 to -3. In the Wilkinson catalyst, the oxidation state of the rhodium is +1.

FAQs (Frequently Asked Questions)

Question 1: What is Wilkinson Catalyst?

Answer: Wilkinson catalyst is the coordinate compound of the rhodium with triphenylphosphine and chloride. The hybridisation possessed by the catalyst is dsp2 and the shape is a square planner.

Question 2: Write the Properties of the Wilkinson Catalyst.

Answer: The properties of Wilkinson catalyst are:

  • Wilkinson catalyst is a solid compound.

  • It exists in the red-brown colour compound.

  • Wilkinson catalyst is sparingly soluble in the polar compound. These are soluble in non-polar organic compounds.

  • Wilkinson catalyst RhCl(PP3)3 gives a reaction with the carbon monoxide (CO) and forms bis (triphenylphosphine) rhodium carbonyl chloride RhCl(CO)(PPh3)2 as a reaction product. This compound can also be formed by the reaction with aldehydes.

RhCl(PPh3)3 + RCHO → RhCl(CO)(PPh3)2 + RH + PPh3