ENHANCEMENT OF INTERFACIAL CATALYSIS IN A BIPHASIC SYSTEM USING CATALYST-BINDING LIGANDS

To avoid the problem of separation of products from catalyst in homoge neous catalysis(1), two-phase systems have been developed in which the catalytic complex (usually a water-soluble organometallic complex) re mains in one (generally aqueous) phase while the products remain in a second, immiscible phase(2). Catalysis relies on the transfer of organ ic substrates into the aqueous catalyst phase; but the limited solubil ity of these substrates in water leads to reaction rates much lower th an those for conventional homogeneous catalysis. Here we show that cat alysis at the interface of a two-phase system can be enhanced by using a 'promoter ligand' which, although soluble in the organic phase, wil l bind to the organometallic catalyst and thus increase its concentrat ion dose to the interface in the aqueous phase. We demonstrate this ap proach for the hydroformylation of 1-octene using a rhodium-based cata lyst. A rate enhancement by a factor of 10-50 is observed when we intr oduce the promoter ligand PPh(3) in the organic phase.