Phosphites hydroformylation

The initial hydroformylation is conducted using tris(2,4-di-/-butylphenyl)phosphite (5) as ligand. 

Rhodium catalyzed reaction of A -butenyl-l,3-propanediamines 397 with a mixture of H2 and CO gave usually a mixture of hydroformylated 398 and 399 and carbonylated products 400 and 401 in the presence of a phosphite [PPha, PBu3, PCCgHiOa, P(o-tol)3] (97TL4315, 97T17449). When the hindered biphosphite, BIPEPHOS, and a 9 1 or 1 1 mixture of H2 and... 

Olivier-Bourbigou s group, for example, has recently shown that phosphite ligands can be used in Rh-catalyzed hydroformylation in ionic liquids as well as the well loiown phosphine systems [81]. Since phosphite ligands are usually unstable in aqueous media, this adds (apart from the much better solubility of higher olefins in... 

In 2000, Claver et al. reported the synthesis of novel chiral S/P ligands with a xylofuranose backbone. These thioether-phosphite ligands derived from carbohydrates were investigated for the rhodium-catalysed hydroformylation of styrene but, in spite of good conversions (>99%) combined with excellent... 

Scheme 10.4 Rh-catalysed hydroformylation of styrene with xylofuranose-derived thioether-phosphite ligands.

Much progress has been made on regioselective hydroformylation of terminal alkenes in favor of the linear product. In particular bidentate phosphine or phosphite ligands, which have a natural bite angle 9 of about 110°, will favor the linear product. The most successful ligand types are BISBI [49, 50], BIPHEPHOS [51,52], and XANTPHOS systems (Scheme 8) [53]. 

Since the mid-1980s bidentate phosphines and phosphites have become very popular as ligands in hydroformylation and many compounds have been spectroscopically identified. The bidentate ligand PPh2NMeCHMeCHPhOPPh2 shown in (57), having two very distinct absorptions for the amido phosphorus and the phosphinite phosphorus nuclei, gives and 31P spectra that are readily interpreted.187... 

Phosphites have been used as ligands in Rh-catalyzed hydroformylation from the early days since their introduction in 1969.205 206 Identification of complexes occurred more recently. Ziolkowski and Trzeciak have studied extensively the use of phosphite ligands in the Rh-catalyzed hydroformylation of alkenes.207-210 The ligand tris(2-/er/-butyl-4-methylphenyl) phosphite (65) leads to extremely fast catalysis and in situ spectroscopy showed that under the reaction conditions only a mono-ligated complex [Rh(H)(CO)3(65)], (66), is formed due the bulkiness of the ligand.211-213... 

Modified rhodium systems show considerable activity in the hydroformylation of styrene to the branched aldehydes. Chiral diphosphines, diphosphites, and phosphine-phosphites have been the ligands most studied. Hydroformylation experiments have often been performed in situ but the characterization of intermediates has provided an interesting contribution to coordination chemistry.179... 

A chiral diphosphite based on binaphthol, coordinated with rhodium (I) forming a nine-member ed ring, led to an efficient hydroformylation of vinylarenes, although moderate ees were obtained (up to 46%) at mild pressure and temperature reaction conditions.364 Chiral diphosphites and phosphinite-phosphites derived from spiro[4.4]nonane-l,6-diol were synthesized. Using these catalysts in the asymmetric hydroformylation of styrene, high regioselectivity (97%) and... 

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... 

Chiral thioether-phosphite ligands (125) derived from 1,2-O-isopropylidenexylofuranose have been synthesized. Reaction of these chiral ligands with [Rh(cod)2]BF4 yielded [Rh(cod)(125)]BF4. These ligands were tested in the Rh-catalyzed hydroformylation of styrene. The hydroformylation results (ee values were insignificant) are discussed according to the solution structure of the species formed under hydroformylation conditions. HP NMR studies show that only the phosphite is coordinated during the catalytic reaction.390... 

Rhodium precipitation in solubilized rhodium-phosphite complex catalyzed liquid recycle hydroformylation may be minimized or prevented by carrying out product recovery in the presence of an organic polymer containing polar functional groups such as amides, ketones, carbamates, ureas and carbonates.[20] Patent examples include the use of polyvinylpyrrolidone and vinylpyrrolidone-vinyl acetate copolymer with diorganophosphite-modified rhodium catalysts. 

A phosphite degradation reaction that occurs during hydroformylation using an aryl-phosphite-modified rhodium catalyst involves replacement of one of the aryl groups with an alkyl group corresponding to the alkyl group of the hydroformylation prod-uct[.[27] This is illustrated in Equation 2.7... 

Equation 2.7. Formation of a poisoning phosphite during propene hydroformylation... 

Poisoning phosphites are particularly undesirable because their smaller steric bulk allows them to bind to the rhodium catalyst and inhibit hydroformylation. 

A method to reduce degradation/deactivation of a phosphite modified rhodium hydroformylation catalyst in the separation system involves feeding a diene such as butadiene to the vaporizer to convert the phosphite-modified rhodium catalyst to a more stable form. [34] In the reactor, the diene is hydrogenated and catalyst activity is restored. 

Figure 3.8. An early example of a hybrid support applied in the rhodium catalysed hydroformylation operated in a continuous flow reactor. Polystyrene containing phosphite ligands were grafted on inorganic silica, such that the catalyst will behave as a homogeneous catalyst when using a compatible solvent...

Nevertheless, the application of ionic liquids in the liquid-liquid, biphasic Rh-catalysed hydroformylation offers technically interesting advantages vs. the traditional aqueous biphasic catalysis e.g. much higher solubility for longer chain olefins and the compatibility of the ionic liquid with phosphite ligands [51]. 

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