Wilkinson's catalyst

Wilkinson's catalyst is the common name for chlorotris(triphenylphosphine)rhodium(I), a chemical compound with the formula RhCl(PPh3)3 (Ph = phenyl). It is named after the late organometallic chemist and 1973 Nobel Laureate, Sir Geoffrey Wilkinson who popularlized its use.

Structure and basic properties
The compound is a square planar, 16-electron complex and is usually isolated in the form of a red-violet crystalline solid from the reaction of rhodium trichloride with triphenylphosphine. The synthesis is conducted in refluxing ethanol. Ethanol serves as the reducing agent.
 * RhCl3(H2O)3 +  CH3CH2OH  +  3 PPh3  &rarr;  RhCl(PPh3)3  +  CH3CHO  +  2 HCl  +  3 H2O

Catalytic applications
Wilkinson's catalyst catalyzes the hydrogenation of alkenes,2 the mechanism of which involves the initial dissociation of one or two triphenylphosphine ligands to give 14 or 12-electron complexes, respectively, followed by oxidative addition of H2 to the metal. Subsequent π-complexation of alkene, intramolecular hydride transfer, and reductive elimination results in extrusion of the alkane product, e.g.:



Other applications of Wilkinson’s catalyst include: catalytic hydroboration of alkenes using catecholborane and pinacolborane,3 and the selective 1,4-reduction of α, β-unsaturated carbonyl compounds in concert with triethylsilane.4

Other reactions of RhCl(PPh3)3
RhCl(Ph3P)3 reacts with CO to give RhCl(CO)(PPh3)2, which is structurally analogous to Vaska's complex. The complex will also decarbonylate aldehydes, although the reaction is stoiochiometric:
 * RhCl(PPh3)3 +  RCHO  &rarr;  RhCl(CO)(PPh3)2  +  RH  +  PPh3

Upon stirring in benzene solution, RhCl(PPh3)3 loses PPh3 to give the poorly soluble red-colored species Rh2Cl2(PPh3)4. This conversion demonstrates the lability of the triphenylphosphine ligands.