Monodentate phosphorus ligands

Van Srijdonck GPF, Boete MDK, van Leeuwen PWN (1999) Fast palladium catalyzed arylation of alkenes using bulky monodentate phosphorus ligands. Eur J Inorg Chem 1073-1076... 

For a perspective on the use of chiral monodentate phosphorus ligands in enantioselective olefin hydrogenations see ... 

There is one more report on the synthesis of a library of phosphorus ligands on solid phase. Waldmann et al. prepared a library of phosphoramidites on beads (Fig. 36.5), but these were only applied in enantioselective C-C-bond formation. In fact, as two ligands need to be bound to the catalyst, the use of an immobilized monodentate ligands should most likely be avoided unless the proximity between the ligands is sufficiently close. In addition, crosslinking by the metal may have a negative impact on the permeability of the polymer for the substrate. 

Breakthroughs that took place around the year 2000 have shown, in contrast to the common view, that indeed chiral monodentate phosphorus ligands can also lead to high enantioselectivities in a number of asymmetric hydrogenations. In the years following, monophosphines, monophos-phonites, monophosphoramidites, and monophosphites have been successfully used in the enantioselective hydrogenation of a-dehydroamino acids and itaconic acid derivatives [25],... 

Thus, we are facing an impossible task to summarize the ligand effect for monodentate phosphines (and phosphorus ligands) and to give credit to the numerous contributions. For the sake of didactics we will present a few rules of thumb, which at this point will not be fully exemplified by literature data, but which will be supported when diphosphines are discussed in section 8.3. 

The use of copper catalysts based on chiral phosphorus ligands to assist 1,4-additions of dialkylzinc reagents has in recent years produced major breakthroughs, with excellent enantioselectivities. A number of monodentate and bidentate phos-phoramidites, phosphites, phosphonites, and phosphines are now available as chiral ligands for alkyl transfer to a variety of cyclic and acyclic enones. So far. 

THE SYNTHESIS AND APPLICATION OF BrXuPHOS A NOVEL MONODENTATE PHOSPHORUS LIGAND FOR THE ASYMMETRIC HYDROGENATION OF KETONES... 

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... 

Recent review about monodentate ligands, see (a) Jerphagnon, T., Renaud, J.-L. and Brrmeau, C. (2004) Chiral monodentate phosphorus ligands for rhodium-catalyzed asymmetric hydrogenation. Tetrahedron Asymmetry, 15, 2101-2111, and references cited therein, (b) de Vries, J.G. (2005)... 

For a historical review on the use of chiral monodentate phosphorus ligands in enantioselectieve olefin hydrogenations, see Komarov, I. V., Borner, A. Angew. Chem., Int. Ed 2001, 40, 1197. 

The infrared spectra of many organocopper compounds have been reported (40, 41, 73, 75, 77) and compared favorably with the respective covalently bound organic halides. Bidentate phosphorus ligands coordinate more strongly with arylcopper compounds than monodentate ligands (41, 75, 281e). Substantial modification of the ligand spectrum is also seen in the infrared spectra of arylcopper complexes with bipy-ridyl or 1,10-phenanthroline (41). 

Bjorsvik, H.R., Hansen, U.M. and Carlson, R. (1997). Principal Properties of Monodentate Phosphorus Ligands. Predictive Model for the Carbonyl Absorption Frequencies in Ni(Co)(3)l Complexes. Acta Chem.Scand.,51,733-741. 

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