Tris lanthanide

Quite a number of asymmetric thiol conjugate addition reactions are known [84], but previous examples of enantioselective thiol conjugate additions were based on the activation of thiol nucleophiles by use of chiral base catalysts such as amino alcohols [85], the lithium thiolate complex of amino bisether [86], and a lanthanide tris(binaphthoxide) [87]. No examples have been reported for the enantioselective thiol conjugate additions through the activation of acceptors by the aid of chiral Lewis acid catalysts. We therefore focussed on the potential of J ,J -DBFOX/ Ph aqua complex catalysts as highly tolerant chiral Lewis acid catalyst in thiol conjugate addition reactions. 

Homoleptic lanthanide(III) tris(amidinates) and guanidinates are among the longest known lanthanide complexes containing these chelating ligands. In this area the carbodiimide insertion route is usually not applicable, as simple, well-defined lanthanide tris(alkyls) and tris(dialkylamides) are not readily available. A notable exception is the formation of homoleptic lanthanide guanidinates from... 

The major synthetic route leading to homoleptic lanthanide tris(amidinates) and guanidinates, however, is the metathetical reaction between anhydrous lanthanide trichlorides and preformed lithium amidinates or guanidinates, respectively, in a molar ratio of 1 3. This is outlined in Scheme 69, showing a samarium(lll) guanidinate as a typical example. ... 

More recently, Aspinah et al. reported the synthesis of a series of lanthanide silsesquioxanes resulting from reactions of 3 with lanthanide tris(silylamides) Ln[N(SiMc3)2]3 (Ln = Y, La, Pr, Eu, Yb). However, single crystals of these materials suitable for X-ray diffraction could not be obtained. The somewhat complicated situation is illustrated in Scheme 25. The lanthanide tris(silylamides) reacted with two-third equivalents of the trisilanol 3 in THF to give the lanthanide silsesquioxanes 85, which are dimeric in solution at 233 K. Reaction of Ln[N(SiMe3)2]3 with one equivalent of 3 in THF resulted in complete conversion of 3 to the trisilylated compound 14, as did the reaction of Ln[N(SiMe3)2]3 with two-third equivalents of 3 in toluene. 

Stevels WM, Ankone MJK, DijkstraPJ, Feijen J (1996) A versatile and highly efficient catalyst system for the preparation of polyesters based on lanthanide tris(2,6-di-tert-butylphenolate) s and various alcohols. Macromolecules 29 3332-3333... 

Metal alkoxides constitute a useful class of starting materials for the synthesis of the metal / -diketonates. The ethoxides of Nbv, Tav and Uv react with diketones. Here, only partial substitution of the ethoxy groups occurs and materials of the type M(diketonate)3(OEt)2 are formed.194,195 Similar reactions with lanthanide alkoxides, however, provide pure, unsolvated lanthanide tris(diketonates). The virtue of such syntheses lies in their ability to yield anhydrous diketonate complexes. Removal of water from the hydrates without decomposition is sometimes difficult.196,197... 

The corresponding homoleptic lanthanide tris(benzamidinates) are accessible in a straightforward manner by reacting anhydrous lanthanide trichlorides with the lithium salts in a 1 3 molar ratio [60] ... 

Scheme 58 Synthesis of homoleptic lanthanide tris(tetramethylaluminate) complexes Ln[(/x-Me)2AlMe2]3 (Ln = Y, La, Ce, Pr, Nd, Sm, Gd, Lu)...

Preformation of homoleptic lanthanide tris(tetramethylaluminate) complexes Ln(AlMe4)3 (Ln = Y, La, Ce, Pr, Nd, Sm, Gd) and Et2AlCl generated extremely active and highly cis-1,4-slcrcosclective binary diene polymerization initiators (Fischbach et al., 2006, personal communication) [150]. Optimal performance in isoprene polymerization was observed for most of the lanthanide metal centers for (Cl) (Ln) ratios of 2 1 (Table 16). Only the samarium... 

Recent advances in the techniques of photoelectron spectroscopy (7) are making it possible to observe ionization from incompletely filled shells of valence elctrons, such as the 3d shell in compounds of first-transition-series elements (2—4) and the 4/ shell in lanthanides (5, 6). It is certain that the study of such ionisations will give much information of interest to chemists. Unfortunately, however, the interpretation of spectra from open-shell molecules is more difficult than for closed-shell species, since, even in the simple one-electron approach to photoelectron spectra, each orbital shell may give rise to several states on ionisation (7). This phenomenon has been particularly studied in the ionisation of core electrons, where for example a molecule (or complex ion in the solid state) with initial spin Si can generate two distinct states, with spin S2=Si — or Si + on ionisation from a non-degenerate core level (8). The analogous effect in valence-shell ionisation was seen by Wertheim et al. in the 4/ band of lanthanide tri-fluorides, LnF3 (9). More recent spectra of lanthanide elements and compounds (6, 9), show a partial resolution of different orbital states, in addition to spin-multiplicity effects. Different orbital states have also been resolved in gas-phase photoelectron spectra of transition-metal sandwich compounds, such as bis-(rr-cyclo-pentadienyl) complexes (3, 4). 

Comparative absorption spectrophotometry has been used in the studies of lanthanide /J-diketonatc complexes in solids as well as in solutions. The neutral hexacoordinated lanthanide tris diketonate on dissolution in a polar nonaqueous solvent, increased its coordination to eight by accepting two solvent molecules [204]. The addition of water or other oxygenated solvent to Nd(diket)3 in solution resulted in significant changes in the shape and intensity of the band due to 4l9/2 —> 4Gis/2, transition. These changes have been attributed to an increase in coordination number of Nd(III) from 6 to 8 by the coordination of two solvent molecules [238-241]. 

The significant nephelauxetic effect in the spectra of Nd(III) hydroxyaquobisbenzoy-lacetonate was attributed to resonance in the /J-diketone by Dutt [238], while the others interpreted this to the lower coordination number of six. Anhydrous lanthanide salts mixed with /1-dikctonatcs of the type (LnL1, L11, L111) show markedly greater nephelauxetic effect and intensity than the lanthanide tris /J-diketonates in semiaqueous media which has been attributed to a lower coordination number in anhydrous /J-diketonates [239,240]. 

The binuclear lanthanide-silver reagent is formed by combining silver diketonate such as Ag(fod) with a lanthanide tris diketonate like Yb(fod)3 to give Ag+[Yb(fod)3]-. 

It is possible that the measured shifts for a substrate with a lanthanide tris(/3-diketonate) can be fit to a unique geometry using the simplified dipolar shift equation. While lanthanide shift data never provided a solution phase system comparable to solid-state X-ray crystallography, the utilization of dipolar shifts with lanthanide shift reagents to understand substrate geometry has been extensive. 

There are many hundreds of published reports on the use of achiral lanthanide tris(/3-diketonates) as NMR shift reagents. Essentially any substrate with an oxygen, nitrogen or sulfur atom is a potential candidate for analysis with lanthanide shift reagents. These include sulfur- and phosphorus-containing functional groups that have oxygen atoms. Carboxylic acids and phenols were observed to decompose lanthanide chelates of dpm, whereas solutions with chelates of fod were stable for several days and suitable for study. 

Chiral lanthanide tris(/ -diketonates) have been used with many classes of organic compounds that have oxygen- and nitrogen-containing functional groups, as well as metal... 

There is the potential with some substrates that the Lewis acidity of the lanthanide ion can catalyze a reaction. For example, the addition of Eu(hfc)3 to a racemic mixture of dimethylpenta-2,3-dienoates (39) caused an enrichment of the (5 )-isomer °. Over nine days the mixture converted to an 89 11 mixture. Lanthanide tris( S-diketonates) are well known catalysts for Diels-Alder reactions, and NMR spectroscopy of the reactants with Eu(hfc)3 was used to understand the stereoselectivity of the europium-catalyzed cycloadditions . ... 

Okano, T., Matsuoka, M., Konishi, H., Kiji, J. Meerwein-Ponndorf-Verley reduction of ketones and aldehydes catalyzed by lanthanide tri-2-propoxides. Chem. Lett. 1987, 181-184. 

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