Thermoregulated hydroformylation

A series of water-soluble polyether-substituted triphenyl phosphines (PETPPs) la-c has been successfully employed by Jin et al. [11] in the thermoregulated hydroformylation of 1-dodecene in the biphasic water/toluene system. The catalysts exhibit very good catalytic properties with conversions up to 93% and about 85% selectivity for aldehyde formation. The catalyst derived from rhodium(III) chloride and ligand Ic could be reused in four consecutive cycles without significant loss of activity or chemoselectivity. The n-selectivity of the product aldehydes was not determined. 

Chiral thioureas have been synthesized and used as ligands for the asymmetric hydroformylation of styrene catalyzed by rhodium(I) complexes. The best results were obtained with /V-phenyl-TV -OS )-(l-phenylethyl)thiourea associated with a cationic rhodium(I) precursor, and asymmetric induction of 40% was then achieved.387,388 Chiral polyether-phosphite ligands derived from (5)-binaphthol were prepared and combined with [Rh(cod)2]BF4. These systems showed high activity, chemo- and regio-selectivity for the catalytic enantioselective hydroformylation of styrene in thermoregulated phase-transfer conditions. Ee values of up to 25% were obtained and recycling was possible without loss of enantioselectivity.389... 

Keywords Immobilization Thermoregulated catalysis Thermomorphic ligands Hydroformylation Polyethylene glycol modified phosphites... 

The use of catechol-based phosphites with PEG moieties in the thermoregulated phase-transfer hydroformylation of 1-decene was also investi-... 

Thermoregulated Phase Transfer Catalysis - A conceptual advance in the field of biphasic hydroformylation of higher olefins is the use of rhodium catalysts generated from nonionic tenside phosphines, such as ethoxylated tris(4-... 

Because of their low solubilities in the aqueous phase, the hydroformylation of higher alkenes (>C2) is still a challenging problem. In addition to fluorous biphasic catalysis, possible solutions, which have been addressed, include the addition of surfactants240,241 or the use of amphiphilic ligands242-244 to enhance mutual solubility or mobility of the components across the phase boundary and thereby increase the rate of reaction. The use of polar solvents such as alcohols,245 p-cyclodextrin,246 cyclodextrin ligands,247 248 thermoregulated phase-transfer... 

Likewise, a thermoregulated phase transfer process within the aqueous/organic two-phase system has been reported by Jin and co-workers (cf. Section 3.1.1.1) [290]. A water-soluble supramolecular Rh catalyst based on functionalized /1-cyclodextrin was also described [291]. In a two-phase system this catalyst may function as a carrier for the transfer of both the starting material and the product between the different phases. As an alternative to polar media for biphasic hydroformylation, Chauvin et al., used ionic liquids based on imidazolium salts which are well known for dimerization reactions (cf. Sections 2.3.1.4 and 3.1.1.2.2) [270, 271, 292]. For introduction into technical processes the currently availability and price of ionic liquids could be a drawback, especially for bulk chemicals such as 0x0 products. 

The development of thermoregulating ligands might well make a decisive contribution to solving the problems of aqueous, homogeneously catalyzed hydroformylations of higher olefins. 

Thermoregulated phase-transfer catalysis, however, could be successfully put into effect for the hydroformylation of higher olefins in aqueous/organic two-phase media [11], As shown in Table 2, various olefins have been converted to the corresponding aldehydes in the presence of nonionic phosphine-modified rhodium complexes as catalysts. An average turnover frequency (TOF) of 250 h-1 for 1-do-decene and 470 Ir1 for styrene have been achieved. Even the hydroformylation of oleyl alcohol, an extremely hydrophobic internal olefin, would give a yield of 72% aldehyde [19]. In comparison, no reaction occurred if Rh/TPPTS complex was used as the catalyst under the same conditions. 

In Lemaire s work, BINOL was used in place of resorcinol to prepare chiral bis(diarylalkylphosphite) end groups on poly(ethylene glycol). When this ligand 141 was combined with [Rh(cod)2]Bp4, a catalyst was obtained that exhibited thermoregulated behavior similar to that seen by Jin with other poly(alkene oxide)-boimd Rh catalysts. However, while high conversions in hydroformyla-tion were observed, the enantioselectivity for the hydroformylation of styrene by the Rh complex of this phosphite 141 was only modest (ca. 25% e.e.). 

FIG. 8 Thermoregulated phase transfer catalysis hydroformylation of higher olefins (Cg-C ). 

The aqueous biphasic hydroformylation of propene, namely the Ruhrchemie/ Rhone Poulenc (RCH/RP) process, has been widely used to produce n-butanal and many attempts have been proposed to improve this catalytic system, such as a thermoregulated phase transfer (TRPT) Rh(I) complex catalyst [74]. Moreover, Bonnemann et al. [75] have proved the in situ formation of Rh colloids when such a catalyst was applied to the aqueous biphasic hydroformylation of 1-octene. 

Breuzard et al. [25] prepared chiral polyether ligands derived from (S)-binaphthol and combined with the [Rh(cod)2]BF4 complex. This system has been used in the catalytic enantioselective hydroformylation of styrene in thermoregulated phase-transfer conditions, but the ee value is less than 25%. 

A thermoregulated phase-separable catalyst formed in situ from P[p-C6H40 (CH2CH20)ioH]3 and RhCl3-3H20 was used in the hydroformylation of diisobutylene. Under the optimum conditions, 93.1% conversion of diisobutylene and 82.5% yield of aldehydes were observed. The catalyst could be efficiently recycled up to three times without any loss of activity [30]. 

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