Rare Earth-Alkali metal heterobimetallic

Structural Analysis of Rare Earth-Alkali Metal Heterobimetallic Complexes... 

Aspinall and coworkers reported detailed structural studies of rare earth-alkali metal heterobimetallic complexes [131]. Whereas the crystal structures provided by Shibasaki and coworkers included one molecule of water coordinating to the central metal, Aspinall and coworkers succeeded in preparing anhydrous crystals of M3[Ln(binol)3] (LnMB). Li3[Ln(binol)3] complexes were obtained from Ln(N(SiMe3)2)3 and Li(Hbinol) in THE or Et20. The resulting HN(SiMe3)2 was removed under reduced pressure, and the crystals were obtained from... 

Scheme 13.40 Preparation methods of rare earth-alkali metal heterobimetallic complexes from various rare earth metal sources.

Scheme 5-47 Asymmetric hydrophosphonylation of a cyclic imine catalyzed by heterobimetallic rare earth/alkali metal/BI-NOL complexes or by chiral titanium alkoxide complexes...

Our preliminary attempts to obtain a basic chiral rare earth complex have led us to create several new chiral heterobimetallic complexes which catalyze various types of asymmetric reactions. The rare earth-alkali metal-tris(l,f-bi-2-naphthoxide) complexes (LnMB, where Ln = rare earth, M = alkali metal, and B = l,l -bi-2-naphthoxide) have been efficiently synthesized from the corresponding metal chloride and/or alkoxide,13,41 and the structures of the LnMB complexes have been unequivocally... 

Scheme 5-45 Asymmetric hydrophosphonyla- nomenclature first letter = rare earth (L=La) tion ofimines catalyzed by heterobimetallic rare second letter = alkali (L = lithium, S = sodium, earth/alkali metal/BINOLcomplexes. Catalyst P = potassium)...

Moreover, these rare earth heterobimetallic complexes can be utilized for a variety of efficient catalytic asymmetric reactions as shown in Scheme 7 Next we began with the development of an amphoteric asymmetric catalyst assembled from aluminum and an alkali metal.1171 The new asymmetric catalyst could be prepared efficiently from LiAlH4 and 2 mol equiv of (R)-BINOL, and the structure was unequivocally determined by X-ray crystallographic analysis (Scheme 8). This aluminum-lithium-BINOL complex (ALB) was highly effective in the Michael reaction of cyclohexenone 75 with dibenzyl malonate 77, giving 82 with 99% ee and 88 % yield at room temperature. Although LLB and... 

For example, an effective procedure for the synthesis of LLB (where LL = lanthanum and lithium) is treatment of LaCls 7H2O with 2.7 mol equiv. BINOL dilithium salt, and NaO-t-Bu (0.3 mol equiv.) in THF at 50 °C for 50 h. Another efficient procedure for the preparation of LLB starts from La(0-/-Pr)3 [54], the exposure of which to 3 mol equiv. BINOL in THF is followed by addition of butyllithium (3 mol equiv.) at 0 C. It is worthy of note that heterobimetallic asymmetric complexes which include LLB are stable in organic solvents such as THF, CH2CI2 and toluene which contain small amounts of water, and are also insensitive to oxygen. These heterobimetallic complexes can, by choice of suitable rare earth and alkali metals, be used to promote a variety of efficient asymmetric reactions, for example nitroaldol, aldol, Michael, nitro-Mannich-type, hydrophosphonylation, hydrophosphination, protonation and Diels-Alder reactions. A catalytic asymmetric nitroaldol reaction, a direct catalytic asymmetric aldol reaction, and a catalytic asymmetric nitro-Mannich-type reaction are discussed in detail below. 

By virtue of a deep understanding of his LnM3tris(BINOLate)3 complexes (Ln = rare-earth metal, M = alkali metal) based on evidence from X-ray analysis and other experiments, Shibasaki developed chiral heterobimetallic yttrium(in) lithium(i) tris(binaphtholate) complex 22, which can promote the catal) ic enantioselective aza-Michael reaction of metho g lamine to enones in excellent yields with up to 97% ee as a Lewis-acid-Lewis-acid cooperative catalyst (Scheme 2.17). Transformation of the 1,4-adducts 23 afforded the corresponding optically active aziridines 24 in high yields. 

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