Chiral phosphine

A similar situation occurs in trivalent phosphorus compounds, or phosphines. It turns out, though, that inversion at phosphorus is substantially slower than Inversion at nitrogen, so stable chiral phosphines can be isolated. (R)- and (5)-metbylpropylphenylphosphine, for example, are configurationally stable for several hours at 100 °C. We ll see the Importance of phosphine chirality in Section 26.7 in connection with the synthesis of chiral amino adds. 

Cone angle concepts, 2,1012-1028 chelate effects, 2,1012 definitions, 2,1015 models, 2,1015 phosphines chiral, 2,1014 polydentate, 2,1013 solubility effects, 2,1014 use, 2,1028... 

Among electron-rich chiral phosphines, chiral phospholanes have emerged to be one of the most efficient classes of ligands in metal catalyzed enantioselective reactions. We have developed a novel family of bisphospholane ligand namely, catASium M, from laboratory to commercial scale. Trimethylsilylphospholane 1 was employed as a key intermediate to provide access to a large variety of ligands. 

The nontrivial synthetic procedures to give the tertiary phosphines chiral at phosphorus (10) led Morrison s group (221, 222) to synthesize neomenthyldiphenylphosphine [(+)-NMDPP] (12) and led Kagan s group (10. 223, 224) to synthesize 2,3-o-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane [(-)-DIOP] (13) from the commercially... 

Knowles next reported optical yields of up to 90% in the hydrogenation of further a-acetamidocinnamic acid derivatives, still using monodentate phosphines chiral at phosphorus. Again the catalysts were prepared in situ from the ligand and [RhCl(l,5-hexadiene)2] or a related complex. The best optical yield of 90% was obtained using cyclohexyl(o-anisyl)methylphosphine (CAMP).224... 

In order to achieve asymmetric hydrogenation, we need to incorporate a chiral phosphine that is capable of distinguishing between the enantiotopic faces of the prochiral olefin, so that one of these faces is coordinated preferentially to the rhodium atom. (It should be noted that the attachment of a prochiral olefin to a metal atom produces a chiral system irrespective of what else is attached to the metal.) Thus the catalyst solution will contain two diastereomeric species, each having the same phosphine chirality but with opposite chiralities of the metal olefin center. Such an equilibrium is shown as Kx in Figure 3. 

Selectivity in enantiotopos-differentiating acylation and phosphorylation of meso-diols can rival that of enzymes. The organocatalysts employed include chiral phosphines, chiral diamines, chiral DMAP derivatives and peptides identified from combinatorial libraries. The highest selectivity in meso diol desymmetrization has been achieved with a planar-chiral Fu catalyst. It seems the substrate scope of this process is not yet broadly explored. Because of their sequential variability it is to be... 

The relatively high optical purities obtained with the Rh-NMDPP system are particularly interesting from a practical viewpoint since the NMDPP ligand is prepared from an inexpensive, commercially available, chiral precursor, (-)-menthol (17). Tertiary phosphines chiral at phosphorus, on the other hand, are much less accessible and require a classic resolution step (see later discussion for details Section II. B). 

Concanavalin, 773 Cone angle concepts, 1012-1028 chelate effects, 1012 definitions, 1015 models, 1015 phosphines chiral, 1014 polydentate, 1013 solubility effects, 1014 use, 1028... 

Fan developed tunable heterobimetallic potassium(i)-crown ether rho-dium(i) catalysts based on a,o)-bis(chiral phosphite) or a,co-(achiral phosphine-chiral phosphite) polyether ligands (Scheme 2.46). For the asymmetric hydrogenation of enamides, catalysts 79 and 80 that showed coordination to the respective metallacrown ethers with the potassium salt... 

Asymmetric hydrogenations of prochiral dehydroamino acid derivatives, enamides, imines, keto esters, and ketones in the presence of synthesized electron-donating phos-phocyclic phosphine ligands and modular atropisomeric biaryl phosphine chiral ligands were reviewed " ... 

Increasing the steric requirement of the substituent at the benzylic carbon ( Bu for Me) produced clear improvement in the resolution of monodentate phosphines chiral at the P atom [29]. The stereochemistry and conformation of these complexes (Figure 4.10) was determined by monodimensional NOE experiments and by analysis of J values. The palladacycle with configuration for the stereogenic C atom showed exclusively the X conformation with both enantiomers of the phosphine. 

Figure 4.10 An orthopalladated complex with a phosphine chiral at the P atom.

---