Phosphorus ligand effects

X. Phosphorus Ligand Effects in Reactions of Nonstabilized Ylides XL Allylic and Benzylic Ylides... 

X. PHOSPHORUS LIGAND EFFECTS IN REACTIONS OF NONSTABILIZED YLIDES... 

Phosphorus Ligand Effects on Z E Selectivity NonstabiIi2ed Ylides from LjP ... 

Steric effects of phosphorus ligands in organometallic chemistry and homogeneous catalysis. C. A. Tolman, Chem. Rev., 1977, 77, 313-348 (298). 

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... 

An excellent review of steric effect of phosphorus ligands on catalytic reaction has been written by Tolman (42). 

Hydrogenation of ct-dehydroamino acid derivatives has been a typical reaction to test the efficiency of new chiral phosphorus ligands. Indeed, a number of chiral phosphorus ligands with great structural diversity are found to be effective for the Rh-catalyzed hydrogenation of a-dehydroamino acid derivatives. Since (Z)-2-(acetamido)cinnamic... 

Amino ketones and their hydrochloride salts can be effectively hydrogenated with chiral rhodium catalysts (Table 33.5). The rhodium precatalysts, when combined with chiral phosphorus ligands such as BPPFOH 4 [20b], hydroxyproline derivatives ligands [20-24], Cy,Cy-oxo-ProNOP 15, Cp,Cp-oxoProNOP 16, and... 

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 vinyl epoxides as substrates in enantioselective copper-catalyzed reactions, on the other hand, has met with more success. An interesting chiral ligand effect on Cu(OTf)2-catalyzed reactions between cyclic vinyloxiranes and dialkylzinc reagents was noted by Feringa et al. [51]. The 2,2 -binaphthyl phosphorus amidite ligands 32 and 43 (Fig. 8.5), which have been successfully used in copper-catalyzed enantioselective conjugate additions to enones [37], allowed kinetic resolution of racemic cyclic vinyloxiranes (Scheme 8.26). 

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