RHODIUM CATALYSED HYDROFORMYLATION

As a result, the second-generation processes used rhodium as the metal. The first rhodium-catalysed, ligand-modified process came on stream in 1974 (Celanese) and more were to follow in 1976 (Union Carbide Corporation) and in 1978 (Mitsubishi Chemical Corporation), all using triphenylphosphine (tpp). The UCC (now Dow) process has been licensed to many other users and it is 

The third generation process concerns the Ruhrchemie/Rhone-Poulenc process utilizing a two-phase system containing water-soluble rhodium-tppts in one phase and the product butanal in the organic phase. The process has been in operation since 1984 by Ruhrchemie (or Celanese, nowadays). The system will be discussed in section 8.2.5. Since 1995 this process is also used for the hydroformylation of 1-butene. 

Diphosphines have also become very popular ligands since the late eighties in rhodium hydroformylation, e.g. Eastman s BISBI. The two-phase system underwent considerable improvements involving diphosphines [9], 

In recent years the interest in hydroformylating higher alkenes with catalysts other than cobalt has increased. Platinum and palladium based catalysts have been studied and the results of the latter [10] seem very promising. Platinum has been known for many years to have a high preference for the formation of linear products, but ligand decomposition hampers applications [11]. 

A ligand with great potential for hydroformylation of higher, terminal alkenes is monosulfonated triphenylphosphine, tppms, that was studied by Abatjoglou, also at Union Carbide [12] (section 8.2.6). In this system hydroformylation is carried out in one phase that is worked up afterwards by adding water, which gives two phases to separate catalyst and product. 

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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... 

In 2000, better results were obtained by Bonnet et al. by using readily available chiral thioureas as new ligands in the asymmetric rhodium-catalysed hydroformylation of styrene. In general, the conversion of styrene and enantioselectivities were modest, but when the reaction was carried out in heptane as the solvent, an enantioselectivity of 41% ee was obtained (Scheme 10.6). 

No attempt is made to provide comprehensive coverage of all the work carried out in these different media, but rather to give a flavour of the kind of systems for which the different approaches may be appropriate. In all the chapters, a more detailed discussion of the rhodium catalysed hydroformylation of 1-octene to nonanal, as a representative example of the synthesis of a long chain aldehyde with relatively low volatility, is provided [13, 14], This reaction has been chosen because ... 

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...

Mesoporous supports have been studied in ligand-free rhodium-catalysed hydroformylation aiming at the stabilisation of specific catalytic species to induce... 

Figure 6.9. Fluorinated ligands used in the rhodium catalysed hydroformylation of alkenes.[44, 45]...

The first investigations of the rhodium-catalysed hydroformylation in room temperature ionic liquids were published by Chauvin et al. in 1995 [44], The hydroformylation of 1-pentene with the neutral catalysts [Rh(CO)2(acac)]/triarylphosphine was carried out in a biphasic reaction using [BMIM][PF6] as the ionic liquid (see Scheme 7.2). 

Rhodium Catalysed Hydroformylation Using Supported Ionic Liquid Phase SILP) Catalysis... 

TABLE 9.1. Rhodium catalysed hydroformylation of 1-octene using a variety of separation methods and catalyst systems compared with results from homogeneous... 

A family of wide bite angle diphosphine ligands based upon xantphos (8) has been developed and tested in rhodium catalysed hydroformylation. van Leeuwen and co-workers conducted HP IR measurements on a range of Rh/thixantphos... 

Replacement of tppts by the fluoro substituted sulfonated ligand 4 [Table 2 94% (n=l) and 6% (n=0)] in the rhodium-catalysed hydroformylation of 1-hexene in a two phase system increased the selectivity to linear aldehyde n-heptanal from 86% to 93% at the low P/Rh molar ratio of 7.5/1.75,76 The Rh/4 catalyst was quantitatively recovered after the reaction by simple decantation.75,76 The moderate increase of the n/i ratio is of interest when one considers that ligand 4 is mainly present as the disulfonated species (94%) compared to the trisulfonated compound tppts and that tris(4-fluorophenyl)phosphine is less basic (pKa=1.97) than triphenylphosphine (pKa=2.73).376 In rhodium-catalysed hydroformylation reactions in organic solvents it is known that electron withdrawing substituents, which increase the -acidity of the ligand, give rise to an increase in the n/i ratio.377 379... 

Figure 6 Rhodium-catalysed hydroformylation of methyl acrylate using various ligands.130-423...

Rhodium-Catalysed Hydroformylation, (2000) (eds. P.W.N.M. van Leeuwen and C. Claver) Kluwer Academic Publishers, Dordrecht. 

In general, in rhodium-catalysed hydroformylation reactions conducted in ionic liquids the catalyst is generated in situ, typically from catalyst precursors such as Rh(OAc)4, or more commonly Rh(acac)(CO)2, together with an excess of an appropriate phosphine ligand. An induction period is often observed with the full activity only being reached after several catalytic runs. This has been attributed to sluggish conversion of the catalyst precursor to the active hydride species,140 421 and to impurities present in the added ligand that are only removed after several product-extraction steps.1401... 

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