Nonionic tensioactive water-soluble phosphines that act as ligands for rhodium-catalyzed hydroformylation of higher olefins under aqueous-organic biphasic conditions are described with emphasis on the recycling efficiency of homogeneous catalyst. Phosphines discussed are P-[p-C6H4(OCH2CH2)nOH]3 (1a: N=3n=18, 1b: N=3n=25) and Ph2P-[p-C6H4(OCH2CH2)nOH] (2a: N=n=16, 2b: N=n=25) (PEO-TPPs). The rhodium catalyst combined with these ligands gave an average turnover frequency (TOF) of 182h-1 for 1-hexene. More importantly, recovery and reuse of catalyst is possible because of the inverse temperature-dependent water solubility of the phosphines.

A brief overview of our recent research results of thermoregulated liquid/liquid biphasic catalysis is presented. Emphasis is given to the general principles of thermoregulated phase-transfer catalysis (TRPTC) and thermoregulated phase-separable catalysis (TPSC). In addition, the applications of TRPTC and TPSC in biphasic catalysis are also discussed. The introduction of TRPTC to biphasic system is free from the shortcomings of classical aqueous/organic two-phase catalysis, in which the application scope is restrained by the water solubility of the substrate. Meanwhile, TPSC provides a very simple and reliable way to deal with the separation of catalyst in homogeneous catalysis. The common advantages of TRPTC and TPSC are characterized by homogeneous catalysis coupled with convenient biphasic separation.

A novel water soluble phosphine, N,N-dipolyoxyethylene-substituted-2-(diphenylphosphino)phenylamine (PEO-DPPPA), was synthesized by a two-step ethoxylation of 2-(diphenylphosphino)phenylamine (2-Ph2P-C6H4NH2, DPPPA). In the first step, DPPPA was ethoxylated without catalyst to give an intermediate with an average polyethylene glycol (PEG) chain length (L=m+n) of 3. Thereafter, this intermediate was further ethoxylated by using KOH as a catalyst to obtain the products with needed values of L. The solubility of the products in water increases with increasing of L. When L is more than 35, the products are water-soluble and possess the property of inverse temperature-dependent solubility in water (cloud point, Cp) as nonionic surfactants. The PEO-DPPPA/Rh complex catalyst formed in situ by RhCl3·3H2O and PEO-DPPPA (L=45) has been applied to the aqueous-organic biphasic hydroformylation of 1-decene. The conversion of olefin and the yield of aldehyde are 99.5 and 99.0%, respectively, under the conditions of 120℃, 5.0MPa (CO/H2=1), P/Rh=4 (molar ratio), 1-decene/Rh=1000 (molar ratio) and 5 h. Recycling test shows that both the conversion of olefin and the yield of aldehyde are still higher than 94.0% even after the catalyst has been recycled 20 times. The high reactivity of PEO-DPPPA/Rh complex can be attributed to a process termed thermoregulated phase transfer catalysis.

Application of the concept of critical solution temperature (CST) of nonionic tensioactive phosphine ligand P[p-C6H4O (CH2CH2)O)nH)3 (PETPP) in the hydroformylation of higher olefins in organic monophase system is presented for the first time. The PETPPrRh complex catalyst is insoluble in organic solvent at room temperature T<CST., on heating to the temperature T>CST, the catalyst would be soluble in organic solvent. Thus, the catalytic reaction would have taken place homogeneously at the reaction temperature (T>CST). When the reaction is completed, on cooling to the room temperature (T<CST), the catalyst would precipitate out from the organic solvent, and could be easily separated from the product and recycled efficiently. Hydroformylation of higher olefins catalyzed by PETPP/Rh complex in organic monophase system is investigated. Under the conditions of T=130℃, P=4.0MPa, the conversion of 1-dodecene and yield of the aldehyde are 95.8% and 93.7%, respectively.