Inter-facial catalysis using various water-compatible ligands in supramolecular systems

In order to hydroformylate heavy alkenes at adequate reaction rates whilst maintaining a water-compatible catalyst in the aqueous phase, we have examined the effect of the addition of small amounts of triphenylphosphine on the water-soluble complexes [Rh-2(CO)(2)(mu-S'Bu)(2)(TPPTS)(2)] and [HRh(CO)(TPPTS)(3)] (TPPTS = tris(3-sulfonatophenyl)phosphine trisodium salt trihydrate). It has been demonstrated that the reaction occurs in the organic phase; an exchange of phosphine restores the starting complex to the aqueous phase but a significant leaching of rhodium into the organic phase occurs. Recycling of the aqueous phase led to a dramatic drop in catalytic activity. Similar studies have been carried out using supported aqueous phase catalysis which involves the immobilization of an aqueous film containing the catalyst on the surface of a hydrophilic support such as silica. We present good evidence that the catalyst operates in 'microreactors', at the interface between the aqueous film and the bulk organic phase. (C) 1999 Elsevier Science S.A. All rights reserved.