Abstract
Catalysis of the reaction between Me 3SiO[Si(H)Me)O] n SiMe 3 ( n ≈ 50) and ethanol by silica-supported rhodium and iridium catalysts has been investigated. Donor groups in the anchored ligands were PPh 2, S −, or C 5H 4 −. The rhodium-PPh 2 system showed marked inhibition by dihydrogen. The supported iridium catalysts all showed high activity which declined rapidly during successive cycles of re-use, but the iridium-PPh 2 catalyst was the least affected. In every case, the separated liquid products showed activity as homogeneous catalysts, indicating that leaching of the metal from the support was occurring. That ligand was also being leached was shown by labelling with tritium. The results demonstrate the necessity to test supported catalysts through more than one cycle.
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