Anchored Wilkinson Catalyst: Hydrogenation of β Pinene

The hydrogenation of beta pinene over homogeneous and anchored Wilkinson's catalysts was studied. Phosphotungstic acid was used to anchor the Wilkinson catalyst to an alumina support by an interaction between the heteropoly acid and the rhodium atom of the complex. The hydrogenation of beta pinene over the anchored catalyst was accompanied by some isomerization to alpha-pinene which was subsequently hydrogenated along with the beta pinene to the pinanes with selectivities to the cis (endo) pinane in the 85-88 % range at near 100 % conversion. With the homogeneous Wilkinson catalyst an 88 % selectivity to cis pinane was also observed but only at 82 % conversion. The use of a 1 % Rh/Al2O3 catalyst for this hydrogenation gave some unexpected results. There was a facile isomerization to alpha pinene which was not hydrogenated further. The reaction stopped at about 30 % conversion at which time the cis and trans pinanes were present in near equal amounts in about 16-18 % yields.