Amphiphilic Diphosphines

Another approach to water-soluble phosphines with the emphasis on metal recycling was reported by van Leeuwen and co-workers [30], They have synthesized a number of diphosphines that, when coordinated to rhodium, form complexes having an amphiphilic character. The ligands synthesized are based on BISBI and Structures 20-22, and hydroformylation (for example) can be conducted in a homogeneous (organic) phase [30 a]. After it has been used in the hydroformylation of olefins the catalyst can be removed by acidic extraction. It was established that these novel diphosphines form active and highly selective catalysts. This amphiphilic approach, i.e., rhodium recycling abased on the extraction and re-extraction principle, will be discussed in more detail in Section 7.5. 

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For the rhodium-catalyzed hydroformylation of higher alkenes, novel amphiphilic diphosphines have been reported (Structure 10-16), based on BISBI (2,2 -bis[di-phenylphosphino]methyl-l,l -biphenyl), XANTHAM, POPpy and POPam, which can be used in the rhodium recycling system [21, 22],... 

Figure 20 (a) Synthesis of the amphiphilic diphosphine (b) Electron microscopy picture of one large and one average sized vesicles... 

Buhling, A. Elgersma, J.W. Nkrumah, S. Kamer, P.C.J. Van Leeuwen, P.W.N.M. (1996) Novel amphiphilic diphosphines synthesis, rhodium complexes, use in hydroformylation and rhodium recycling, Dalton Trans., 2143-54. 

Fluorous diphosphine complexes [Rh(COD)(12)]BF4 showed amphiphilic behavior, resulting in the formation of aggregates with a size of several hundreds... 

The reaction which is accelerated by the presence of water can be carried out in water when a 2/3-cyclodextrin-[Rh(OH)(cod)]2,943,944 [Rh(cod)Cl]2/TPPTS,945 or amphiphilic resin-supported rhodium(i) complex was used.946 It was also reported that potassium alkenyl and aryltrifluoroborates [RBF3]K undergo similar addition to enones in the presence of an Rh(i) catalyst.935,947,948 The cationic rhodium(i) complexes such as [Rh(cod)]BF4, [Rh(cod)(CH3CN)2]BF4, or its combination with a diphosphine ligand (dppp or dppb) efficiently catalyzed the reaction. The neutral complexes, generated in situ from Rh(acac)(GH2=GH2)2, or Rh(acac)(coe)2, and dppp or dppb, were also effective. The effects of catalysts, solvents, and bases,949 and the mechanism of catalytic cycle950 have been studied in detail. 

Amphiphilic diblock copolymers based on 2-oxazoline derivatives with chiral diphosphine 187 were prepared (Scheme 3.61) and used in the asymmetric hydrogenation of methyl (Z)-(z-acelarnido cinnamate 188 in water to give the (R)-phenylalanine derivative 189 in 85% ee [124]. The polymeric catalyst could be recycled. This result illustrated the advantages of using amphiphihc copolymers for the efficient transformation of a hydrophobic substrate in water. 

Rhodium(I) complexes, prepared from [Rh(cod)2][BF4] and from amphiphilic, (3-CD modified diphosphines, were used as catalysts for the competing hydrogenation of 4-phenyl- and 4-cyclohexyl-1-butene in two-phase water/substrate mixtures (Eq. 30) [75],... 

All BISBI-type diphosphine-modified catalysts give selectivities around 90% to linear aldehydes. As can be seen in Table 1, POP (2,2 -bis(diphenylphosphino)-diethyl ether) and its amphiphilic derivatives give rise to mainly linear aldehyde (88-89%). Although the selectivity for linear aldehydes is moderate compared with XANTHOS (9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene), virtually no isomerization is observed. 

Also, 1-dodecene can be selectively reacted with syngas in the presence of a Rh(BIPHEPHOS) catalyst to give n-tridecanal (Table 6.1, entry 5). A related Rh catalyst based on nanoparticles (2.7-4.8 nm) could be three times recycled without loss of activity when the reaction was conducted in a thermomorphic solvent system [61]. Also, under the conditions illustrated in Scheme 6.6 ( = 4), tridecanal is formed, but in comparison to shorter chain olefins the conversion dropped and the aldehyde was obtained only in a moderate Ub ratio [54]. Other attempts have been based on more sophistic ligands such as amphiphilic sulfonated monophosphines [62] and diphosphines [55, 63], phosphine-functionalized phosphonium ionic liquids [64], and MeO-substituted phosphines [65]. Tridecanal has a slightly floral scent reminiscent of citrus and grapefruit peel. 

Ir [39], and Rh [40] carbenes for Pt [63]. Fluorinated amines allowed stabilizing Ru [64] and Pt [65] NPs showing good solubility in fluorinated solvents. Amphiphilic ligands such as l,3,5-triaza-7-phosphaadamantane (PTA) [66] as well as sulfonated diphosphines [55] and cyclodextrins (CDs) [67] allowed to obtain water-soluble NPs by simple isolation of the particles preformed in organic phase and their dissolution in water. Ru NPs were also synthesized in imidazolium-derived ILs [68,69],... 

Regarding sustainability concerns, inspiration was taken from aqueous organometallic catalytic systems. To obtain water-soluble NPs for catalysis in aqueous phase while starting their synthesis in organic solvent given the nature of the metal precursors, the alternative was to employ amphiphilic ligands such as PTA, sulfonated diphosphines, and CDs, which are known to stabilize water-soluble complexes. 

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