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It is extensively used as a catalyst in the hydrogenation of alkenes.

Wilkinson’s Catalyst [IUPAC Name: chloridotris(triphenylphosphine)rhodium(I)] is a coordination compound whose coordination centre is rhodium. It is extensively used as a catalyst in the hydrogenation of alkenes. The chemical formula of Wilkinson’s catalyst can be written as [RhCl(PPh 3 ) 3 ] where ‘Ph’ denotes a phenyl group. At ambient temperatures, this coordination complex exists as a reddish-brown solid.

Wilkinson’s catalyst is named after the English chemist Sir Geoffrey Wilkinson. Its structure is illustrated below.

It can be noted that as per single-crystal X-ray diffraction studies, the structure adopted by Wilkinson’s Catalyst is square planar (slightly distorted). The rhodium centre is bound to four ligands in this compound.

Wilkinson’s catalyst can be prepared by reacting hydrated rhodium(III) chloride with excess triphenylphosphine in the presence of ethanol (which acts as a refluxing agent). Here, the triphenylphosphine (denoted by the chemical formula P(C 6 H 5 ) 3 ) acts as a reducing agent which has the ability to oxidize itself from an oxidation state of +3 to an oxidation state of +5.

During the synthesis of Wilkinson’s catalyst, one equivalent of triphenylphosphine reduces rhodium(III) to rhodium(I) while three other equivalents bind themselves to the metal as ligands in the final product.

4P(C 6 H 5 ) 3 + RhCl 3 (H 2 O) 3 → RhCl(P(C 6 H 5 ) 3 ) 3 + OP(C 6 H 5 ) 3 + 2HCl + 2H 2 O

The chemical reaction for the synthesis of Wilkinson’s catalyst is provided above.

An illustration detailing the mechanism of action of Wilkinson’s catalyst for the hydrogenation of olefins is provided above.

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