Question

What is the difference between Wilkinson’s catalyst and H2/Pd/C? Give an example.

Answer 1

Wilkinsons catalyst: Wilkinson's catalyst, is the complex chloridotris(triphenylphosphane)rhodium(I) which is a coordination complex of rhodium with the formula RhCl(PPh3)3. This catalyst is known for catalyzing the hydrogenation of olefins with molecular hydrogen and useful for homogeneous catalysis. The addition of hydrogen across the double bond is from same side ie. syn manner and hence, it is more useful for assymmetric hydrogenation. Further, it selectively prefer to hydrogenate the less hindered alkene due to stearic point of view. Hence, Internal and branched alkenes (alkynes) are hydrogenated slower than terminal alkenes (alkynes).

H2/Pd Hydrogenation: This is highly active heterogeneous catalysts often cannot achieve high levels of selectivity. The addition of hydrogen across the double or triple bond is not specific and hence, hydrogenation product may be mixture of stereoisomers.