Monodentate phosphorus-based ligand

One of the most common methods for the preparation of enantiomerically enriched organosilanes is by palladium-catalysed asymmetric hydrosilylation of alkenes in the presence of trichlorosilane. This area has been dominated by the use of monodentate phosphorus-based ligands and, in particular, Hayashi s MOP ligand/palladium catalyst combination offers a high level of enantioselectivity. The MOP ligands include MeO-MOP (2.139), H-MOP ligands such as (2.140) ... 

The enantioselective reduction of N acetyl enamides has a rich history and several substrate classes of N acetyl enamides can now be reliably converted to enantiopure amines (>99% ee) using rhodium based catalysts. The field has bifurcated over the past 10 years with the utility of monodentate versus bidentate ligands at the fore of the discussion. In Chapter 8, Zhou lays a strong foundation for the monodentate phosphorus ligand accomplishments and challenges. Chapter 9 provides a wonder fill complement by Zheng, who fully summarizes the bidentate phosphorus ligand literature over the past 10 years. 

It thus came as a surprise that in the year 2000, three groups independently reported the use of three new classes of monodentate ligands (Scheme 28.2) [12], The ligands induced remarkably high enantioselectivities, comparable to those obtained using the best bidentate phosphines, in the rhodium-catalyzed enantioselective alkene hydrogenation. All three being based on a BINOL backbone, and devoid of chirality on phosphorus, these monophosphonites [13], monophosphites [14] and monophosphoramidites [15] are very easy to prepare and are equipped with a variable alkyl, alkoxy, or amine functionality, respectively. 

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. 

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... 

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