Selectivity in hydroformylation

It must be emphasized that the above considerations were made in the absence of reaction. Interfacial mass transfer followed by reaction requires further consideration. The Hatta regimes classify transfer-reaction situations into infinitely slow transport compared to reaction (Hatta category A) to infinitely fast transport compared to reaction (Hatta category H) [42]. In the first case all reaction occurs at the interface and in the second all reaction occurs in the bulk fluid. Homogenous catalytic hydrogenations, carbonylations etc. require consideration of this issue. An extreme example of the severity of mass transport effects on reactivity and selectivity in hydroformylation has been provided by Chaudari [43]. Further general discussions for homogeneous catalysis can be found elsewhere [39[. 

A. W. Kleij, M. Lutz, A. L. Spek, P. W. N. M. van Leeuwen, J. N. H. Reek, Encapsulated transition metal catalysts comprising peripheral Zn(ll)salen building blocks template-control-led reactivity and selectivity in hydroformylation catalysis, Chem. Common., 2005, 3661. 

Another example of the use of metal complexes in ionic liquids was reported by Moores and co-workers. In this case, besides the use of [P4 4 4 i4]NTf2 as the solvent, different diphenylphosphino functionalised phosphonium salts (Fig. 3) acted as monodentate ligand for Rh complexes. These PFILs-Rh(I) complexes displayed very good activities and excellent selectivities in hydroformylation reactions. 

The 0x0 process is employed to produce higher alcohols from linear and branched higher olefins. Using a catalyst that is highly selective for hydroformylation of linear olefins at the terminal carbon atom. Shell converts olefins from the Shell higher olefin process (SHOP) to alcohols. This results in a product that is up to 75—85% linear when a linear feedstock is employed. Other 0x0 processes, such as those employed by ICI, Exxon, and BASE (all in Europe), produce oxo-alcohols from a-olefin feedstocks such alcohols have a linearity of about 60%. Enichem, on the other hand, produces... 

Pla.tinum. Platinum catalysts that utilize both phosphine and tin(Il) haUde ligands give good rates and selectivities, in contrast to platinum alone, which has extremely low or nonexistent hydroformylation activity. High specificity to the linear aldehyde from 1-pentene or 1-heptene is obtained using HPtSnClgCO(1 1P) (26), active at 100°C and 20 MPa (290 psi) producing 95% -hexanal from 1-pentene. 

For long chain olefins, the hydroformylation generally proceeds slowly and with low selectivity in two-phase systems due to their poor solubility in water. Monflier et al. recently reported a conversion of up to 100% and a regioselectivity of up to 95% for the Rh-catalyzed hydroformylation of dec-l-ene in water, free of organic solvent, in the presence of partially methylated 6-cyclodextrins (Eq. 3.42).173... 

A variant of the BISBI ligand system is the NAPHOS ligand, which as expected gives similar levels of n-selectivity in the course of the hydroformylation of terminal alkenes. Interesting is a hydroformylation in the presence of secondary amines which allows a mild and selective one-pot hydroformy-lation/enamine formation (Scheme 13) [58]. 

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... 

Platinum complexes with chiral phosphorus ligands have been extensively used in asymmetric hydroformylation. In most cases, styrene has been used as the substrate to evaluate the efficiency of the catalyst systems. In addition, styrere was of interest as a model intermediate in the synthesis of arylpropionic acids, a family of anti-inflammatory drugs.308,309 Until 1993 the best enantio-selectivities in asymmetric hydroformylation were provided by platinum complexes, although the activities and regioselectivities were, in many cases, far from the obtained for rhodium catalysts. A report on asymmetric carbonylation was published in 1993.310 Two reviews dedicated to asymmetric hydroformylation, which appeared in 1995, include the most important studies and results on platinum-catalogued asymmetric hydroformylation.80,81 A report appeared in 1999 about hydrocarbonylation of carbon-carbon double bonds catalyzed by Ptn complexes, including a proposal for a mechanism for this process.311... 

The method of catalyst immobilisation appeared to affect its performance in catalysis. Catalyst obtained by method II showed a low selectivity in the hydroformylation of 1-octene (l b aldehyde ratio was even lower than 2) at a very high rate and high yields of isomerised alkenes (Table 3.2, entry 2), whereas procedure IV resulted in a catalyst that was highly selective for the linear aldehyde (with a l b ratio of 37) (entry 5). In accordance with examples from literature it is likely that procedure II gave rise to the ionic bonding of ligand-free rhodium cations on the slightly acidic silica surface [29],... 

TABLE 3.6. Comparison of the activity and selectivity in the hydroformylation of linear alkenes using homogeneous [HRh(CO)(PPh3)3] and [HRh(CO)(PPh3)3] encapsulated in MCM-48 a... 

A fundamental topic in hydroformylation research is the control of regio-selectivity and the suppression of side-reactions like the hydrogenation reac-... 

However, platinum catalysts have several disadvantages they have low reaction rates, they hydrogenate the substrate and their regioselectivity to the branched aldehyde is low. The selectivity of Pt-diphosphite/SnCl2 systems is also low. When the appropriate diphosphite is used, ee s can be as high as 90% [13]. In the early 90s, several reports were published which described the state of the art in hydroformylation with both rhodium and platinum systems [14-16]. 

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