Dissymmetric diphosphine

By using the dissymmetric diphosphine l-diphenylphosphino-2-tert-butyl-3-dicy-clohexylphosphinoprop-l-ene, van Leeuwen has demonstrated that the insertion of CO into Pd-Me proceeds via migration of the hydrocarbyl group to the CO ligand [24]. 

Reaction of phosphinite borane 42 (Table 4.2, entry 43) with 1-bromo-l -lithioferrocene afforded the monophosphine borane 43 (Table 4.4, entry 50), which still possesses a bromine atom susceptible to metallation on the non-phosphinated Cp ring. After lithiation, the ferrocenyl anion reacted with the second phosphinite borane 44 (Table 4.2, entry 44), affording the desired optically pure dissymmetric diphosphine borane 45 in 29% yield from 42. During the synthesis impurities such as undesired monosubstituted ferrocene derivatives could be separated by column chromatography. 

Dissymmetric ferrocenyldiphosphines have been synthesized from (R)-(+)-N, N -dimethylaminoethylferrocene. The diphosphines have been used as ligands in asymmetric transfer hydrogenation of acetophenone in the presence of ruthenium catalysts.297 Asymmetric transfer hydrogenation of a,/S-unsaturated aldehydes with Hantzsch dihydropyridines and a catalytic amount of MacMillan imidazolidinone salt (12) leads to the saturated carbonyl compounds in high yields and excellent chemo-and enantio-selectivities.298 ... 

The BINAP ligand 5 (Figure 1) has numerous unique features. The diphosphine is characterized by full aromatic substitution, which exerts steric influence, provides polarizability, and enhances the Lewis acidity of the metal complex. The BINAP molecule is conformationally flexible and can accommodate a wide variety of transition metals by rotation about the binaphthyl C(1)-C(T) pivot and C(2 or 2 )-P bonds without a serious increase in torsional strain. The framework of the chiral ligand determines enantioselectivity but can also alter the reactivity of the metal complex. In addition, the BINAP binaphthyl groups are axially dissymmetric possessing Cj symmetry,14 resulting in the production of an excellent asymmetric environment.lf... 

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