Hydroformylation trans-4-octene

Phosphacyclic diphosphines (73a) and (73b) with wide natural bite angles were synthesized and the effect of the phosphacyclic moieties on the coordination chemistry in the [(diphosphine) Rh(CO)2H] complexes was studied. Both NMR and IR spectroscopy showed that the phosphacyclic xantphos ligands exhibit an enhanced preference for diequatorial chelation compared to the diphenylphosphino-substituted parent compound. In the hydroformylation of 1-octene the introduction of the phosphacyclic moieties leads to higher reaction rates. The dibenzophospholyl- and phenoxaphosphino-substituted xantphos ligands exhibit a high activity and selectivity in the hydroformylation of trans-2- and 4-octene to linear nonanal. CO dissociation rates from the... 

Recently, we reported that the rhodium/BIPHEPHOS-catalyzed hydroformylation of trans-4-octene (Scheme 6) provides an interesting approach for the synthesis of n-nonanal [23]. In this context trans-4-octene can also be seen as a model substance for hydroformylation of internally unsaturated fatty acid esters. This could open up access to the use of renewable resources for the synthesis of valuable n-aldehydes. 

Using mild reaction conditions (10 bar, 125 °C), a high conversion of trans-4-octene and a high selectivity to n-nonanal can be obtained with toluene as the solvent. Cyclic carbonates like propylene carbonate (PC) are also suitable solvents for the isomerizing hydroformylation of trans-4-octene. Furthermore, the selectivity to -nonanal is increased up to 95% when PC is used in a single phase. The product n-nonanal can be extracted with n-dodecane or with a mixture of dodecane isomers. 

Propylene carbonate is a good solvent of the rhodium precursor [Rh(acac) (00)2] and the phosphite ligand BIPHEPHOS and can thus be used as the catalyst phase in the investigation of the isomerizing hydroformylation of trans-4-octene to n-nonanal in a biphasic system [24]. As already mentioned, the reaction products can be extracted with the hydrocarbon dodecane. Instead of an additional extraction after the catalytic reaction, we carried out in-situ extraction experiments, where the products are separated from the catalytic propylene carbonate phase while the reaction is still in progress. Conversion of 96% and selectivity of 72% was achieved under comparably mild conditions (p(CO/H2) = 10 bar, T = 125 °C, 4 h, substrate/Rh = 200 1). 

With increasing concentration of methylated /1-cyclodextrin the selectivity to n-nonanal increases from 64% to 72%, while the conversion of the olefin is constantly as high as 97%. Obviously the addition of the methylated /i-cyclodextrin has only a moderate influence on the isomerizing hydroformylation of trans-4-octene to n-nonanal. The addition of only 0.2 mol.-% of methylated /3-cyclodextrin lowers the isomerization rate which results in the formation of slightly more branched aldehydes. In pharmacy j6-cyclodextrins are established as solvation mediators between polar and less polar solvents. This is one possible explanation for the rise in selectivity to n-nonanal with an increasing j6-cyclodextrin concentration. At higher con-... 

To elucidate the use of TMS systems for the isomerizing hydroformylation, PC was chosen as the solvent for the rhodium catalyst, because the best selectivity to n-nonanal of 95% with a conversion on trans-4-octene of also 95% was achieved in this solvent under single-phase conditions. Dodecane was used as a non-polar solvent for the extraction of the product and p-xylene served as the mediator between the catalyst and the product phase [24]. Appropriate operation points for the reaction within this solvent system were determined by cloud titrations. 

Fig. 7 Isomerizing hydroformylation of trans-4-octene in the IMS system PC/dodecane/ p-xylene...

Table 10 Hydroformylation of trans-4-octene in cyclic carbonate/N-octyl-2-pyrrolidone/ extraction agent, T = 125 °C, p(syngas, 1 1) = 10bar, t(reaction) = 4h, m(solvents) = 30 g, n([Rh(acac)(CO)2]) = lO- mol, n(BIPHEPHOS) = 5 x mol...

Suitable thermomorphic solvent systems were appUed to the telomeriza-tion of butadiene with ethylene glycol or with carbon dioxide, to the isomer-izing hydroformylation of trans-4-octene and to the hydroaminomethylation of 1-octene with morpholine. Further investigations for the carboxytelomer-ization and for the synthesis of 4-nitrodiphenylamine were also carried out. In addition to common Ugands, PEG-modified ligands and fiuorous Ugands were used for the telomerization and the carboxytelomerization. 

The hydroformylation of trflns-3-octene at room temperature using the (non-encapsulated) rhodium catalyst based on tris(weta-pyridyl)phosphine afforded 2-ethylheptana] and 2-propylhexanal in exactly a 1 1 ratio. The encapsulated catalyst provided an unprecedented selectivity for 2-propylhexanal of 75% (Scheme 8.3). Again the selectivity is largely retained at 40 °C whereas at 80 °C the isomerization side reaction prohibits the selective formation of aldehydes. Similar regioselectivities were obtained in the hydroformylation of frflns-2-hexene, trans-2-nonene and trans-3-nonene at 25 °C. 

Other Substrates. a-Methylstyrene, a-ethylstyrene, allylbenzene, trans-/ -methylstyrene, 1-pentene, and 1-octene were hydroformylated as described for styrene, giving the results reported in Tables III and IV. 

Figure 7.22 Results for the continuous hydroformylation of 1-octene catalysed by Rh/P(4-C6H4C6Fi3)3 in fluorocarbon solvents. (1 = linear isomer, b = branched isomer) [Reprinted with permission from Dalton Trans., 2004, 2062-2064. Copyright 2004 The Royal Society of Chemistry.]...

Various papers describe the aqueous biphasic hydroformylation for simple olefins as well as for functionalized olefins or dienes [154-174] (cf. the Section 6.1). In recent work [175], the synthesis of n-nonanal by consecutive isomerization and hydroformylation reactions of trans-4-octene has been described. The catalyst used was the in situ combination of Rh(acac)(CO)2 and the chelate phosphite BIPHE-PHOS. Performing the reaction in propylene carbonate the selectivity to n-nonanal could be raised up to 95%. If after the reaction the product is extracted with dodec-... 

The biphasic hydroformylation of water-insoluble internal olefins was also achieved using the above temporarily supramolecular host which appeared to be more efficient than the second-sphere ligand RAME-/3-CD. The initial activities obtained with the above caltxarene derivative were improved by a factor of 3.5 compared to RAME-/3-CD for the case of trans-4-octene but the selectivities were similar for both systems. 

The consecutive isomerization-hydroformylation reaction of trans-4-octene yields high conversion and high selectivity of n-nonanal in the polar solvent propene carbonate [Eq. (8)] [33]. 

Using the complexes in hydroformylation not only increased the reaction rate in comparison with their analogues produced as mixtures but also improved the selectivity with respect to linear aldehyde owing to the orientation of the substrate in cyclodextrin. Unlike catalysis by low molecular weight analogues, the reaction involves even alkenes with an internal double bond (trans-3-octene). The catalyst was highly soluble in water, mainly remained in the aqueous phase after the reaction and can be reused. 

Parlevliet FJ, Kiener C, Fraanje J, Goubitz K, Lutz M, Spek AL, Kamer PCJ, Van Leeuwen PWNM. Calix[4]arene based monophosphites, identification of three conformations and their use in the rhodium-catalysed hydroformylation of 1-octene. J Chem Soc Dalton Trans 2000 7 1113-22. 

The electronic properties of phosphinines are located between those of phosphines and phosphites, with somewhat more similarity to phosphites. In general, phosphinines are characterized by considerable it-acceptor properties and thus beneficial for several catalytic applications [32]. A theoretical study on Rh-phosphinine complexes provided evidence that the directionality of the ir-backdonation rather than the overall acceptor ability was responsible for the high catalytic activity [33]. In the rhodium-catalyzed hydroformylation of styrene with phosphinines as ligands, superior results in terms of conversion and TOP (turnover frequency) were noted in comparison to the use of PPhj or standard mono-triarylphosphites [34]. Atropisomeric 2-arylphosphmines have been prepared by Muller s group [35]. In the hydroformylation of trans-2-octene, a clear preference for the formation of 2-methyloctanal was noted. 

A famous example of a ligand structure that promotes the isomeriza-tion-hydroformylation reaction sequence in a highly selective manner is the BIPHEPHOS ligand (Scheme 6.14.6). BIPHEPHOS has been demonstrated to convert trans-4-octene into 1-nonanal with a remarkably high selectivity of 89% (given the complex reaction scheme) (Behr et al., 2003). However, the Rh-BIPHEPHOS hydroformylation system for trans-4-octene is relatively slow (TOF = 46h ), leaving room for further ligand optimization to make combined isomerization/hydroformylation processes more efficient. 

Scheme 6.14.6 Isomerization/hydroformylation of trans-4-octene using a Rh-BIPHEPHOS catalyst. Adapted from Behr etal. (2003).

Behr, A., Obst, D., Schulte, C., and Schosser, T. (2003) Highly selective tandem isomerization-hydroformylation reaction of trans-4-octene to n-nonanal with rhodium-BIPHEPHOS catalysis. J, Mol, Catal, A-Chem, 206, 179-184. 

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