Hydroformylation ligand effects

The hydrolytic decomposition of a potential fluorophosphite ligand would generate free fluoride ions which would be expected to be detrimental to the activity of a hydroformylation catalyst. The patent literature contains abundant references to the detrimental effects of halogens (6) on hydroformylation catalysts, and based on the patent information, one could not reasonably expect a halophosphite to be a successful hydroformylation ligand. However, a second publication by Klender (7) shows that exposure of / and other fluorophosphites to moisture at temperatures of 250°C to 350°C does not generate fluoride, even at part per million levels. 

Foca CM, Barros HJV, dos Santos EN, Gusevskaya EV, Carles Bayon J (2003) Hydroformylation of myreene metal and ligand effects in the hydroformylation of conjugated dienes. New J Chem 27(3) 533-539... 

Ligand effects of diphosphines have been reported by Unruh and Christensen. They studied the hydroformylation of 1-hexene using substituted ferrocene derived diphosphines Fe sHiPRah (Fig. 6.4). 

Unmh and Christenson studied the unusual chelating phosphine ligand l,k-bis(diphenylphosphino)ferrocene and found several interesting effects on Rh-catalyzed hydroformylation. The effect of excess ligand on rate and selectivity is shown in Table 4. 

For a good discussion of the modified hydroformylation process including an analysis of phosphine ligand effects, see C. Masters, Homogeneous Transition-Metal Catalysis—A Gentle Art, Chapman Hall London, 1981, pp. 114-120. 

In the final example, we shall consider kinetics and ligand effects in the cobalt-catalyzed hydroformylation of olefins. The mrmodified cobalt catalyst in this case is [HCo(CO)4], which dissociates witii loss of CO in an equilibrium reaction (Eq. 2-97). 

Hydroformylation is also a model reaction system in homogeneous catalysis as it contains so many aspects such as ligand effects (electronic, steric, bite angle), in situ studies, complicated kinetics, and effects of conditions and impurities. All this, combined with its practical value, makes it an ideal topic in education. 

In contrast to their effect of rhodium-catalyzed hydroformylation, organic ligands effect on the cobalt-catalyzed reaction is less pronounced. Moreover, a desired regiodirecting effect strongly depends on the equilibrium between the modified and unmodified catalyst. 

In 1999, Casado et al. developed heterotetranuclear complexes (TiRh3) depicted in Scheme 10.3 with bridging sullido ligands combined with P-donor ligands. These complexes were further tested as catalysts for the asymmetric hydroformylation reaction of styrene. In this process, [CpTi((/i3-S)3 Rh(tfbb 3] was efficiently active under mild conditions (10 bar, CO/H2 = 1 atm, 353 K). In order to explore the effect of the added phosphorus ligand and the possibilities of this system for the asymmetric hydroformylation of styrene, achiral diphosphines such as dppe (l,2-bis(diphenylphosphine)ethane) and... 

The ligands synthesized were also apphed to the isomerizing hydroformylation of more reactive 2-pentene. At 120 °C/ 20 bar quantitative conversion of olefin to aldehydes was achieved within 40 min. Trends similar to those described for internal octene hydroformylation were found. The regioselectivity obtained for the individual ligands tends to be 5% higher compared to that for the octenes. Thus, in the presence of 10 75% of n-hexanal were determined, compare Table 3. Obviously, 2-pentene is able to react more smoothly to the terminal isomer compared to olefins having the double bond in an more internal position. Illustrative for this effect are also literature results obtained for 2- and 4-octene.4,5... 

Structure (43) (QPCH2CH2PQ) (Q = mixture of 1,4- and 1,5-cyclooctanediyl) was reported to be a very effective ligand for the palladium catalyzed hydroformylation of internal and terminal alkenes using small amounts of NaCl or HC1 as an additive in PhOMe or diglyme as the solvent.138-141... 

Various bifunctional potentially hemilabile ligands (72) bearing phosphorus groups were prepared and their coordination to rhodium was studied. Their effect on the hydroformylation of styrene was assessed.237... 

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... 

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