Hydroformylation phosphorus ligands

In contrast to other areas of hydroformylation chemistry, in dendrimer-based hydroformylation phosphorus ligands play a role not only as ligating groups for rhodium but also as scaffolds with amine- or amino alcohol functionahty [120]. Moreover, nanoparticles, colloids, or mesoporous silica have been used to stabilize unmodified [121] or phosphine (e.g., PPhj, diphenylphosphinophenylsulfonate)-modified rhodium complexes [122]. 

Hydroformylation has been extensively studied since it produces optically active aldehydes which could be important precursors for pharmaceutical and fine chemical compounds. Thus, asymmetric hydroformylation of styrene (Scheme 27) is a model reaction for the synthesis of ibuprofen or naproxen. Phosphorus ligands were used for this reaction with excellent results, espe-... 

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... 

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... 

Highly enantioselective hydroformylation catalyzed by chiral metal complexes has been obtained with only a few catalytic systems. Many chiral phosphorus ligands have been used in Pt(II) and Rh(I) systems in the asymmetric hydroformylation of styrene. The first highly enantioselective examples of the asymmetric hydroformylation of styrene were reported by Consiglio et al. in 1991 and used Pt-Sn systems. ligand 1 achieved an ee of 86% (Fig. 1) [10-12],... 

However, considerable amounts of 2,3-dihydrofuran 50 and tetrahydro-furan-2-carbaldehyde 53 were present because of an isomerization process. The isomerization takes place simultaneously with the hydroformylation reaction. When the 2,5-dihydrofuran 46 reacts with the rhodium hydride complex, the 3-alkyl intermediate 48 is formed. This can evolve to the 2,3-dihydrofuran 50 via /3-hydride elimination reaction. This new substrate can also give both 2- and 3-alkyl intermediates 52 and 48, respectively. Although the formation of the 3-alkyl intermediate 48 is thermodynamically favored, the acylation occurs faster in the 2-alkyl intermediates 52. Regio-selectivity is therefore dominated by the rate of formation of the acyl complexes. The modification of the phosphorus ligand and the conditions of the reaction make it possible to control the regioselectivity and prepare the 2- or 3-substituted aldehyde as the major product [78]. As far as we know, only two... 

The discovery and use of fluorophosphites and chlorophosphites as trivalent phosphorus ligands in the rhodium catalyzed, low-pressure hydroformylation reaction are described. The hydroformylation reaction with halophosphite ligands has been demonstrated with terminal and internal olefins. For the hydroformylation of propylene, the linear to branched ratio of the butyraldehyde product shows a strong dependency on the ligand to rhodium molar ratios, the reaction temperature, and the carbon monoxide partial pressure. 

Industrial efforts have been focused on manufacturing of t>r/ 7/-aldehydes ( linear aldehydes) from olefins. Here, we briefly summarize its history on the development of phosphorus ligands, which are classified as monophosphine, monophosphite, bis-phosphite, and bis-phosphine, all useful for the normal-sc cct vc hydroformylation. 

Assemblies based on 8 and pyridine phosphorus ligands 5-7 were used as supramolecular ligands in the rhodium-catalyzed hydroformylation and showed typical bidentate behavior. The chelating bidentate assembly exhibited lower activities (a factor of three) than the monodentate analogue. Only a slightly higher selectivity for the linear aldehyde was observed. The chiral ligand assemblies based... 

Analogues of [RhH(CO)(PPh3)3] with other phosphorus ligands also act as hydroformylation catalysts. Using complex (34) in the presence of l,l -bis(diphenylphosphino)ferrocene as ligand,... 

The new hybrid phosphorus ligand (74), prepared from NOBIN (2-amino-2,-hy-droxy-1,1 -hinaphthyl),105 has been reported to exhibit excellent enantioselectivities (up to 99% ee) in the Rh-catalysed asymmetric hydroformylations of styrene deriva- tives and vinyl acetate.106... 

In the Shell process (SHOP) phosphine-modified cobalt-catalyzed hydrofor-mylation is one of the steps in the synthesis of linear alcohols with 12-15 carbon atoms (see Section 7.4.1). Two important characteristics of this reaction should be noted. First, the phosphine-modified precatalyst HCo(CO)3(PBu3) is less active for hydroformylation than HCo(CO)4 but more active for the subsequent hydrogenation of the aldehyde. In this catalytic system both hydroformylation and hydrogenation of the aldehyde are catalyzed by the same catalytic species. Second, the phosphorus ligand-substituted derivatives are more stable than their carbonyl analogues at higher temperatures and lower pressures (see Table 5.1). 

ARCO An intermediate for 1,4-butanediol Rhodium catalyst with chelating phosphorus ligand hydroformylation of allyl alcohol followed by hydrogenation of the resultant aldehyde Reaction 5.9... 

Kuraray An intermediate for 3-methyl 1,5-pentane diol Rh4(CO)12 with phosphorus ligand as the precatalyst hydroformylation of 2-methyl buten-4-ol followed by hydrogenation Reaction 5.10... 

The two metals that have been found to give encouraging conversions and selectivities for the hydroformylation of styrene are platinum and rhodium. The platinum-based catalytic system uses tin chloride as a promoter. It also uses triethyl orthoformate as a scavenger that reacts with the aldehyde to form the acetal. By removing it as soon as it is formed, any further degradative reactions of the aldehyde are avoided. The chirality in these reactions is induced by the use of optically active phosphorus ligands. With the best platinum catalyst, branched and linear aldehydes are produced in about equal proportion, but the former has an e.e. of >96%. 

Figure 9.13 Proposed catalytic cycle for asymmetric hydroformylation reaction with [Rh(acac)(P-P)] as the precatalyst. The chelating chiral phosphorus ligand could be 9.45 or 9.46. acac = acetylacetonato anion.

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