Chirality lanthanide complexes with chiral

Although the development of a variety of Lewis acids has enabled the reahzation of a wide range of catalytic asymmetric reactions, most of the catalysts have limited activity in terms of either enantioselectivity or chemical yields. The major difference between synthetic asymmetric catalysts and enzymes is that the former activates only one side of the substrate in an intermolecular reaction, whereas the latter not only can activate both sides of the substrate but also can control the orientation of the substrate. If this kind of synergistic cooperation could be realized in synthetic asymmetric catalysis, it would open up a new field in asymmetric synthesis, and a wide range of applications might well ensure. In this section we discuss asymmetric two-center catalysis promoted by chiral lanthanide complexes with Lewis acidity and Brpnsted basicity [44,45]. 

Lanthanide complexes with heterocyclic ligands in molecular recognition and chirality sensing of biological substrates 02CRV2389. 

Lanthanide complexes with optically active -diketones have been used to determine the purity of optical isomers see chap. 4, p. 87 of Ref. 2 for a review). The most widely used chiral shift reagents are based on 3-trifiuoroacetyl-d-camphor, the anion of which is designated facam. The crystal structure determination of the DMF adduct of tris(3-tri-fiuoroacetyl-d-camphorato) praseodymium (III), the first of a chiral shift reagent, has been completed (31). The asymmetric unit contains the dimer, (facam)sPr(DMF)3Pr(facam)3, with the DMF oxygen atoms forming bridges between the two Pr(facam)3 moieties. Therefore, each Pr(III) ion is nine-coordinate with a geometry best described as a capped... 

It is unfortunate that there is to date no generally applicable spectra-structure correlations for CPL measurements from lanthanide (HI) complexes. However, the number of chiral lanthanide complexes with well-understood geometry and solution dynamics is increasing, al-... 

Petoud S, Muller G, Moore EG et al (2007) Brilliant Sm, Eu, Tb, and Dy chiral lanthanide complexes with strong circularly polarized luminescence. J Am Chem Soc 129 77-83... 

Danishefsky et al. were probably the first to observe that lanthanide complexes can catalyze the cycloaddition reaction of aldehydes with activated dienes [24]. The reaction of benzaldehyde la with activated conjugated dienes such as 2d was found to be catalyzed by Eu(hfc)3 16 giving up to 58% ee (Scheme 4.16). The ee of the cycloaddition products for other substrates was in the range 20-40% with 1 mol% loading of 16. Catalyst 16 has also been used for diastereoselective cycloaddition reactions using chiral 0-menthoxy-activated dienes derived from (-)-menthol, giving up to 84% de [24b,c] it has also been used for the synthesis of optically pure saccharides. 

Few investigations have included chiral lanthanide complexes as catalysts for cycloaddition reactions of activated aldehydes [42]. The reaction of tert-butyl glyoxylate with Danishefsky s diene gave the expected cycloaddition product in up to 88% yield and 66% ee when a chiral yttrium bis-trifluoromethanesulfonylamide complex was used as the catalyst. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

In this reaction, a rhodium atom complexed to a chiral diphosphine ligand ( P—P ) catalyzes the hydrogenation of a prochiral enamide, with essentially complete enan-tioselectivity and limiting kinetic rates exceeding hundreds of catalyst turnovers per second. While precious metals such as Ru, Rh, and Ir are notably effective for catalysis of hydrogenation reactions, many other transition-metal and lanthanide complexes exhibit similar potency. 

Inanaga, J. Furuno, H. Hayano, T. Asymmetric catalysis and amplification with chiral lanthanide complexes. Chem. Rev. 2002,102, 2211-2225. 

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