Monodentate phosphite ligands

Monodentate phosphites are another type of prominent monodentate phosphorus ligands applied in asymmetric hydrogenation of enamides for the synthesis of chiral amines. Chiral monodentate phosphites can be easily prepared from a chiral diol and an alcohol. Generally, the chiral diol was first reacted with a phosphorus trichloride to form a phosphorochloridite, followed by the reaction with an appropriate alcohol to yield a chiral monodentate phosphite [35[. The reaction of an alcohol with phos phorus trichoride to yield a phosphorodichloridite, which was then treated with a chiral diol, is also a good procedure for the synthesis of chiral monodentate phosphites [36]. 

The rhodium catalyzed asymmetric hydrogenation of terminal arylenamides 7 by using monophosphite ligand 30 provided chiral N acetyl arylamines 8 with 

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Switching the roles of the zinc porphyrin template and N-donor adapter provides an alternative mode for the supramolecular construction of biden-tate ligands (Scheme 32). Complex 26 derived from mixing three equivalents of template 24 with two equivalents of monodentate phosphite ligands 23 furnished a rhodium catalyst which displayed good regioselectivity toward... 

Scheme 28.6 Monodentate phosphite ligands derived from BINOL or related diols.

As described for monodentate phosphonite ligands, monodentate phosphite ligands have also been used in a monodentate ligand combination approach. 

Scheme 28.8 Monodentate phosphite ligands based on carbohydrates.

Reetz and Goossen et al. reported recently the asymmetric hydrogenation of a series of enol esters using monodentate phosphite ligands 17 and 24 based on a combination of BINOL and carbohydrates or simple alcohols the results of these studies are shown in Table 28.6. 

The same nanofiltration experiments were performed with a 50-A ultrafiltration membrane (available from US Filter/Membralox, Warrendale, PA,USA), this time with a monodentate phosphite ligand (24) used for comparison and toluene as the solvent (Table V). Both higher retentions and flux rates for the dendrimers were obtained relative to what was observed with the reverse osmosis membranes. Dendrophite G4 was used in three subsequent reactions carried out with this procedure. 

Mono- and dihydroaminomethylation of olefins was performed with dicarbonyl-2,4-pentanedionerhodium containing a monodentate phosphite ligand as the catalyst under moderate pressures. The reaction has high region-specificity with yields exceeding 90%. 

Scheme 7.5 Spiro monodentate phosphite ligands and the putative stereorecognition model for the rhodium-catalyzed asymmetric addition of arylboronic acids to aldehydes, as described by Zhou and coworkers [8].

The mechanism and the scope of the hydrocyanation and 2-methyl-3-butenenitrile isomerization reaction has been studied at DuPont in great detail for nickel catalysts featuring monodentate phosphite ligands, such as P(Otolyl)3. The results of these studies have been published in a review by Tolman and coworkers [9]. Later advances in the field have been summarized in recent reviews [10, 11], and book chapters [12, 13]. The aim of this chapter is to give an account of those developments that have not been covered in these reviews yet or are directly relevant to our own SFB-based research conducted in the field. 

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