The dissociation of a phosphine ligand from (B) results in the formation of the coordinatively unsaturated complex (C), which then forms the alkene complex (D). It involves the oxidative addition of H2 to the 16-electron complex RhCl(PPh3)3, to form the 18-electron dihydrido complex (B). The dominant cycle for the hydrogenation of terminal alkenes by Wilkinson’s catalyst is shown in Fig.

This useful catalyst leads to the hydrogenation of a wide variety of alkenes and alkynes at pressures of hydrogen close to 1 atm or less at room temperature. In either case, they become isoelectronic with the next noble gas, i.e., they achieve an 18-electron valence shell configuration. They can become five-coordinate through the simple addition of a ligand or six-coordinate through addition combined with oxidation. It is a square planar 16-electron d8 complex Chlorotris(triphenylphosphine)rhodium(I). One of the most studied catalytic systems is the Rh(I) complex, which is often referred to as Wilkinson’s catalyst. What catalyst is used in the hydrogenation of alkenes? The metal may be deposited on the inert solid support such as alumina or calcium carbonate.Įfficient homogeneous and heterogeneous catalysts are known for the hydrogenation of alkenes and are used in such diverse areas as the manufacture of nondairy spreads, pharmaceuticals, and petrochemicals. However, the reaction rate is negligible at ordinary conditions in the absence of a catalyst, but in the presence of metallic nickel, copper, palladium or platinum, the reaction is fast and complete.

The addition of hydrogen to an alkene to form an alkane is favoured thermodynamically (ΔrGθ = -101 kJ mol-1 for the conversion of ethene to ethane), it does take place at room temperature and pressure.

Key points: Wilkinson’s catalyst,, and related complexes are used for the hydrogenation of a wide variety of alkenes at pressures of hydrogen close to 1 atm or less suitable chiral ligands can lead to enantioselective hydrogenations.

Wilkinson catalyst reaction with alkene