Investigations into the recovery of Wilkinson's catalyst with silica-immobilised P-donor ligands

摘要

Three PPh_2 functionalities, immobilised through a C2 (1), C3 (2), and C5 (3) spacer onto silica, have been studied for their capacity to recover Wilkinson's catalyst. A low surface concentration of the ligand together with a short spacer arm gave the best recovery results, as under these conditions the formation of stable RhL_2 and Rh_2L_2 complexes is precluded. The silica immobilised phosphorus ligands are oxidised under the rhodium extraction conditions, dependent on the presence of rhodium ions and the silica backbone, while no oxidation occurs when using phosphorus ligands anchored on an organic backbone.