Lanthanide complexes 3-diketonate, chiral

Lipophilic lanthanide complexes of fluorinated 3-diketonate ligands were demonstrated to bind unprotected amino acids under neutral conditions. It is not clear whether amino acids are bound as anions or zwitterions. Chiral ligands 63-66 have been prepared and tested for extraction of amino acids from water into dichloromethane [84] (Table 7). NMR and CD spectroscopic... 

Bis- -diketones have been demonstrated to be powerful ligands in the engineering of supramolecular architectures. Pikramenou and coworkers [53a] used two bis-P-diketones of l,3-bis(3-phenyl-3-oxopropanoyl)benzene (H2L ) and l,3-bis(3-phenyl-3-oxopropanoyl) 5-ethoxy-benzene (H2L ) to synthesize neutral homodimetallic complexes [Ln2(L )3] (Ln = Eu, Nd, Sm, Y, Gd) and [Ln2(L )3] (Ln = Eu, Nd) and also an anionic dinuclear lanthanide complex [Eu2(L )4] . The detailed studies by NMR, electrospray, and MALDI (matrix assisted laser desorption ionization) mass spectrometry, by addition of chiral Pirkle s reagent, revealed that [Ln2(L" )3] and [Eu2(L )4] (see Eigure 2.38) are chiral, and have triple- and quadruple-stranded supramolecular structures, respectively, with the latter being more strongly emissive than the former. 

Lanthanide /3-diketonates containing fluorinated chiral camphor-derived ligands (61, M = Pr, Eu, Er, Yb, R = Mef, n-Prf) form highly coordinated 14 complexes with zwitterionic, unprotected phenylalanine, leucine, and other amino acids under neutral conditions. This allows extraction of the amino acids from their neutral aqueous solutions into dichloromethane phases . 

LnCpa and Cp2LnCl complexes initiate the dehalogenation of aiyl and vinyl halides by NaH. Chemoselectivity is observed in the reduction of m-bromochloro-benzene and p-iodochlorobenzene to chlorobenzene [192], The asymmetric reduction of methylphenyl glyoxylate to methyl mandelate by NADH models is catalyzed by chiral lanthanide )6-diketonates [193],... 

Progress has been made in the search for new lanthanide /3-diketonates as sources of luminescence, with application in the fabrication of polymer light-emitting diodes for low-cost, full-color, flat-panel displays.16,17 Moreover, some complexes seem promising as chiral NMR reagents for the determination of enantiomeric purity18,19 and prospective catalysts in many organic syntheses.20... 

The first asymmetric catalyst to be evaluated was the commercially available chiral lanthanide P-diketonate complex Eu(hfc)3 [10]. The initial result was obtained from the reaction of benzaldehyde with diene 5, which showed 18% enantiomeric excess [11]. Attempts to improve the asymmetric induction by varying the substituents on the diene were undertaken (Scheme 4). Substitution at either C2 or C4 of the diene seemed to increase the asymmetric induction. By using the... 

The first catalyst to be evaluated was the commercially available chiral lanthanide p-diketonate complex Eu(hfc)3. The reaction of benzaldehyde with diene (8) was chosen as the system to screen various catalysts for their enantiofacial selectivity. A simple method to assess the extent and sense of the optical induction was also developed. This was accomplished by optical and NMR measurements on compound (68), obtained from (64) and (65) by a previously described protocol (Scheme 22).- - - The en-antioselectivity with diene (8) and benzaldehyde is 18%. ... 

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... 

Reagents formed with chiral /3 -diketonate ligands such as Lnftfcfs and Ln(hfc)3 in the presence of Ag(fod) or other silver /3-diketonates are effective for chiral discrimination . Lanthanide chelates with dcm are ineffective in the binuclear complexes, presumably because the dcm ligand is so sterically hindered that it prevents the formation of the quadruple chelate anion. Silver complexes besides Ag(fod) actually form more effective chiral discriminating agents with Pr(tfc)3, Yb(tfc)3 and Yb(hfc)3, but these complexes are not commercially available so have not been used beyond exploratory studies . ... 

The use of ZnCh and (3-diketonate complexes of lanthanide metals give predominately endo-type addition products and CF diastereofacial selectivity. The CF stereoselectivity seems to prevail in cases using ZnCh as a catalyst and chiral aldehydes that contain groups that do not chelate to the metal. The selectivity clearly decreases when aldehydes that can form chelates are used. The lanthanide catalysts also exhibit strong CF-type selectivity with nonchelating chiral aldehydes. This trend seems to hold with most chelating aldehydes however, ACF products have been reported when a-alkoxy aldehydes are used in the reaction.56 The stereochemical consequences of using lanthanide catalysts with a-alkoxy aldehydes are therefore not predictable. 

By the reaction of theenolatc of camphor with carboxylic acid esters or chlorides, 1,3-diketones [better formulated as enols. such as (hydroxymethylene)camphor] are obtained. When trifluo-roacetic acid or heptafluorobutanoic acid are used, the corresponding diketones (abbreviated as tfc or hfc, respectively) have been successfully used as ligands for lanthanides and these are used as chiral shift reagents in NMR spectroscopy12. The complex Eu(hfc)3 [derived from ( + )-camphor)] 3 was used as a chiral catalyst for enantioselective Diels-Alder-type cycloadditions of aldehydes to dienes (Section D.l.6.1.1.1.2.4.). 

Bimetallic complexes formed using a lanthanide tris (3-diketonate and silver 3-diketonate are useful shift reagents for soft Lewis bases such as alkenes, aromatics, phosphines, and halogenated compounds.Chiral lanthanide tris (3-diketonates of tfc and hfc are used in forming the binuclear reagents. A variety of silver 3-diketonates have been evaluated, but only the silver chelate of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione [Ag (fod)] is commercially available. The mixture forms a tetrakis chelate anion to which the silver is ion paired ([Ln (P-dik)4 ]Ag" "). In the bimetallic reagent, the silver binds to the soft Lewis base while the paramagnetic lanthanide ion causes perturbations in the chemical shifts that account for the enantiomeric discrimination. 

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