Ligands in hydroformylation

Since the mid-1980s bidentate phosphines and phosphites have become very popular as ligands in hydroformylation and many compounds have been spectroscopically identified. The bidentate ligand PPh2NMeCHMeCHPhOPPh2 shown in (57), having two very distinct absorptions for the amido phosphorus and the phosphinite phosphorus nuclei, gives and 31P spectra that are readily interpreted.187... 

The above results were reviewed in 1974 (5). Since then the main advances in the field have been the achievement of asymmetric hydro-carbalkoxylation (see Scheme I, X = -OR) using palladium catalysts in the presence of (-)DIOP (6), the use of other diphosphines as asymmetric ligands in hydroformylation by rhodium (7), and the achievement of the platinum-catalyzed asymmetric hydroformylation (8, 9). Further work in the field of asymmetric hydroformylation with rhodium catalysts has been directed mainly towards improving optical yields using different asymmetric ligands (10), while only very few efforts were devoted to asymmetric hydroformylation catalyzed by cobalt or other metals (11, 12) and it will be discussed in a modified form in this chapter. 

Transition metal complexes with heterocycles as ligands in hydroformylation including hydroformylation of heterocycles 02CCR(228)61, 03CCR(241)295. 

Separation and Use of Water-insoluble Ammonium Ligands in Hydroformylation... 

Table IS. Dependence of Product Distribution on Phosphorus Ligand in Hydroformylation of 1-Octene° ...

There are very many investigations in the literature concerning the evaluation of different metals and associated organic ligands in hydroformylation. In 2013, Franke and Seller [1] provided a concise summary about the applicability of alternative metals in hydroformylation. In the same year, another survey was assembled by a joint French/Italian cooperation [2]. In order to avoid a full repetition, only some basic conclusions will be mentioned here, which are not in the focus of the reviews cited above. 

Only a few studies are known concerning the application of triphosphines as ligands in hydroformylation. Their behavior resembles in principle the effect of three monodentate phosphines coordinated to rhodium. For... 

Here, mainly hydrolysis of phosphites that have been used as ligands in hydroformylation will be considered. Dialkylphosphites, which are also prone to hydrolysis in basic and neutral conditions but are rather stable toward acids, will not be reviewed [133]. 

Phosphoramidites are a class of widely used ligands in hydroformylation. In contrast to phosphites, their synthesis is frequently more convenient. With substituents on the nitrogen, additional electronic and steric tuning is possible. Especially this feature has been advantageously employed in the asymmetric version of hydroformylation. Of particular interest is the reduced stability of phosphoramidites toward water, which can be inferior to that of phosphites. 

Figure 2.54 Azolium salts, the corresponding NHCs, and a non-NHC precursor used as preligands or ligands in hydroformylation.

Electron-rich phosphines were not expected to be good ligands in hydroformylation, because the complexes they form of the type HRh(CO)x(L)4- are very stable towards dissociation of either CO or L (L=alkylphosphine) due to a push-puU effect of the donor and acceptor ligand combination. Cole-Hamilton and coworkers [82] found activity for alkylphosphine complexes when RhH(PEt3)3 was used as the precursor, but at higher temperatures as expected. Under the reaction conditions RhH(CO)(PEt3)3 is the major species present. When the reactions are carried out in alcohols the product of the reaction is the... 

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