Hydroformylation of Internal Olefins

To achieve a considerable result for internal olefin hydroformylation, it is generally accepted that the catalytic system should meet the following requirements (i) the isomerization of the internal olefin to the terminal olefin must be faster than the hydroformylation reaction (ii) the hydroformylation of the terminal olefin must be faster than any other hydroformylation reaction and (iii) the activity and selectivity of the catalyst for the hydroformylation of the terminal olefin must be really good. 

Nevertheless, few examples of successful catalysts showing acceptable results for the hydroformylation of internal olefins in the biphasic catalytic systems have been reported to date. This is due to many causes. First, the suUbnation of ligands could be a difficulty. Moreover, the high temperature is a positive factor for the isomerization reaction of internal olefins but may be a cause for the rhodium loss and leaching into the organic phase in the biphasic hydroformylation. Seller and Krauter studied the hydroformylation of 2-pentene in an aqueous biphasic system with a Co/TPPTS catalyst in 1999. A linear to branched ratio (n/i) of up to 75 25 was obtained at 100 °C and 100 bar CO/Hj [83]. The catalyst was reused up to four times without loss of activity. Inspirationally, they reported for the first time 

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A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

Fig. 11 Some recent developments for isomerizing hydroformylation of internal olefins...

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

The results of the hydroformylation of internal olefins are reported in Table 9. In the case of (Z)- and (E)-2-butene, the same fare of the unsaturated carbon atom is formylated with either a rhodium- or platinum (—)-DIOP-containing catalytic system. With the rhodium catalyst, when an acyclic olefin is used as the substrate, the same fare is always attacked, and it is only the notation but not the geometric requirement that is different for (E)-l-phenyl-1-propene. The only exception is represented by bicyclo[2,2,l]heptene. However, using (—)-CHIRAPHOS instead of (—)-DIOP, also bieyelo[2,2,l]heptene behaves like internal butenes. No regularity is observed for the cobalt or ruthenium (—)-DIOP catalytic systems. With the same system, only in 3 cases out of 15 the face of the prochiral atom preferentially formylated has different geometric requirements. 

Recently van Leeuwen reported the fiigt crystal structure of the diphosphite dicarbonyl rhodium catalyst HRh(CO)2(P P) [258]. Bomer et al. developed a new class of phosphonites which show promising results for the isomerization and subsequent hydroformylation of internal olefins [259]. The number of phosphite ligands based on supramolecular backbones such as calix[4]arenes is growing [260]. They are attractive because of their well defined structure combined with the ability to adopt several discrete conformations. Calix[4]arene diphosphites and calix[6]arene phosphites were first developed by BASF [261]. In... 

In the hydroformylation of internal olefins, only CoH(CO)4 and CoafCOfs were observed spectroscopically, suggesting that in these cases the rate-determining step is conversion of CoH(CO)4 to the alkyltetracarbonyl [reaction (b )]> with undetectable, steady state concentrations of the other species. The reaction of styrene with CoH(CO)4 and CO yields the a-phenylpropionylcobalt derivative Co(COCHMePh)(CO)4, which partially isomerizes to the -phenylpropionyl derivative Co(COCH2CH2Ph)(CO)4- This sequence establishes that acyl derivatives of cobalt(I) can be prepared from CoH(CO)4, olefin, and carbon monoxide, as for the combined steps of reactions (b ) and (b")-... 

More than one decade after Parshall s work, Knifton demonstrated the crucial role played by the addition of quaternary phosphonium salts in the hydroformylation of internal olefins catalyzed by ruthenium melt [27]. In the system described, the anionic ruthenium cluster [HRu3(CO)jj] generated in situ from [RUO2], [Ru(OAc)2], or [Ru(acac)3] is the predominant metal carbonyl species in the reactant solutions. 

Phosphonium ionic liquids have been used several times for metal-catalyzed hydroformylations. Ruthenium and cobalt metal complexes catalyze the hydroformylation of internal olefins in [ Bu4P][Br] the major products are, however, the corresponding alcohols. Rhodium-catalyzed hydroformylations were conducted in [Bu3PEt][TsO] and [Ph3PEt][TsO] melts (meltingpoints 8UC and94 C, respectively). The products were easily isolated by decantation of the solid medium at room temperature. ... 

Yan Y, Zhang X, Zhang X (2006) A tetraphosphorus ligand for highly regioselective isomerization-hydroformylation of internal olefins. J Am Chem Soc 128 16058-16061... 

Reactions of internal olefins can even generate terminal alkylnitriles by a pathway that involves isomerization of intermediate cyanometal-alkyl complexes. Tlus isomerization is similar to the isomerization that occurs during the hydroformylation of internal olefins discussed in Chapter 17. In fact, the nickel catalyst rapidly isomerizes hexene to the equilibrium ratio of olefins faster than it adds HCN to the C=C bond. Thus, internal hexenes generate the terminal alkane nitrile. 

Two other reactions are discussed here for specific reasons. Hydroformylation of internal olefins to yield terminal aldehydes is a difficult task since it requires isomerization prior to hydroformylation. Only a few attempts are known to tackle this problem in aqueous—organic two-phase systems despite the great industrial interest in using 2-butenes as starting material for valeraldehyde. The Rh-TPPTS catalyst is rather unreactive toward internal olefins, however [Co2(CO)6(TPPTS)2] prepared from [Co2(CO)8] and TPPTS proved effective in hydroformylation of 2-pentenes to isomeric Ce-aldehydes and a small amount of the... 

The formation of more than two aldehyde isomers can also be expected if hydrogen shift on the substrate occurs during hydroformylation of internal olefins. 

Halide anions affect the rate of the hydroformylation of internal olefins as well as its chemo- and regioselectivity [7]. The rate of hydroformylation of thermally equilibrated internal higher alkenes increased by a factor of 6-7 by the addition of substoichiometric amounts (with respect to palladium) of Cl or Br and about a factor of 3-4 with I . Moreover, the selectivity toward the formation of the alcohol was dramatically increased. Highest yields of alcohols were noted with the assistance of iodide. Only traces of alkanes were formed. Up to now, a general explanation of the effect could not be given, but it seems that it is also dependent on the diphosphine ligand used. 

Du Pont and DSM [105] claimed the preparation and use of binaphthyl-derived diphosphites for isomerization-hydroformylation of internal olefins llb = 36 with 2-hexene) and methyl 3-pentenoate, respectively (Scheme 5.19). In general. 

Scheme 6.14.5 Selective hydroformylation of internal olefins to n-aldehydes. Adapted from Klein etal. (2001).

Mein, H., Jackstell, R., Wiese, K.-D., Borg-mann, C., and BeDer, M. (2001) Highly selective catalyst systems for the hydroformylation of internal olefins to linear aldehydes. Angew. Chem. Int. Ed., 40 (18), 3408-3411. 

Finally, Union Carbide has developed the hydroformylation of internal olefins by rhodium catalysis using very bulky phosphites. Given the present burst of asymmetric catalysis, the search of adequate chiral ligands for asymmetric hydroformylation of prochiral olefins achieving high e.e.s is a real challenge. 

Tang, S.C. and Kim, L. (1982) Homogeneous hydroformylation of internal olefins by platinum tin cationic complexes. Journal cf Molecular Catalysis. 

Stabilizing the catalyst against acids was needed for the Rh/BINAS-catalyzed aqueous hydroformylation of internal olefins (see Table 5.1) [8]. Reaction rates were low (averaged TOF = 62h for 2-pentene), but very high regioselectivities of 99% toward the terminal aldehydes were obtained for the hydroformylation of 2-pentene and 2-octene, respectively, under optimized reaction conditions. Controlling pH was found to be essential to increase both the selectivity and the aldehyde yield. Best results were obtained in solutions buffered at pH 8-9, or with additional triethanolamine or TMEDA employed to trap formic acid suggested to be formed in a side reaction. 

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