Insight into Phosphine Effects on the Homogeneous Hydrogenation of Avermectins to Ivermectin Catalyzed by In-Situ Formed Rhodium Complexes

Abstract

A kinetic study of the homogeneous catalytic hydrogenation of avermectins is reported for a series of isosteric p-substituted arylphosphines as ligands. The activity of the rhodium complexes formed in situ from [RhCl(COD)]2 increased with increasing the electron-donor capacity of the P(p-XC6H4)3: P(p-ClC6H4)3 < P(C6H5)3 < P(p-CH3C6H4)3 < P(p-OCH3C6H4)3. As expected, this trend was also observed when using preformed complexes thereof. Linear correlations based on Hammett and Kabachnik treatments are provided as useful tools to guide the exploration work towards improved [RhCl(COD)]2/P(p-XC6H4)3 catalytic systems.