Tetranuclear titanium 7,7′‐modified binaphtholate cluster as a novel chiral Lewis acid catalyst

Mikami, Kōichi; Ueki, Makoto; Matsumoto, Y.; Terada, Masahiro

doi:10.1002/chir.1174

Cited by 40 publications

(32 citation statements)

References 9 publications

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“…Studies with racemic binol led these authors to observe several heterochiral species [(binolate) 6 Ti 4 (m 3 -OH) 4 ], in agreement with the reported NLE in this reaction. [135] Mikami et al had previously isolated this complex, which catalyzed [2+3] nitrone cycloadditions, [136] and its tetranuclear structure was confirmed by X-ray analysis. Subsequently, Yudin and coworkers [137] employed the analogous complex [(F 8 binolate) 6 Ti 4 O 4 ] as a sulfoxidation catalyst, whose structure was established by X-ray crystallography.…”

Section: Sulfoxidationmentioning

confidence: 78%

Nonlinear Effects in Asymmetric Catalysis

Satyanarayana¹,

Abraham²,

Kagan³

2008

Angew Chem Int Ed

488

273

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There is a need for the preparation of enantiomerically pure compounds for various applications. An efficient approach to achieve this goal is asymmetric catalysis. The chiral catalyst is usually prepared from a chiral auxiliary, which itself is derived from a natural product or by resolution of a racemic precursor. The use of non-enantiopure chiral auxiliaries in asymmetric catalysis seems unattractive to preparative chemists, since the anticipated enantiomeric excess (ee) of the reaction product should be proportional to the ee value of the chiral auxiliary (linearity). In fact, some deviation from linearity may arise. Such nonlinear effects can be rich in mechanistic information and can be synthetically useful (asymmetric amplification). This Review documents the advances made during the last decade in the use of nonlinear effects in the area of organometallic and organic catalysis.

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Section: Sulfoxidationmentioning

confidence: 78%

Nonlinear Effects in Asymmetric Catalysis

Satyanarayana¹,

Abraham²,

Kagan³

2008

Angew Chem Int Ed

488

273

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“…[3,6,20] At this time, the catalytic activity and/or relevance of the hydroxide-bridged compounds to reactions catalyzed by M 3 A C H T U N G T R E N N U N G (THF) n A C H T U N G T R E N N U N G (BINOLate) 3 Yb [M = Li and K] is unclear. On the basis of recent reports using the tetrameric clusters Zr 4 A C H T U N G T R E N N U N G (BINOLate) 6 A C H T U N G T R E N N U N G (m 3 -OH) 4 [25] and Ti 4 A C H T U N G T R E N N U N G (BINOLate) 6 A C H T U N G T R E N N U N G (m 3 -OH) 4 [26,27] as stable and effective catalyst in organic reactions, one should remain mindful of the potential formation and influence of hydroxide-bridged oligomers in asymmetric reactions when water is used as an additive with M 3 A C H T U N G T R E N N U N G (THF) n A C H T U N G T R E N N U N G (BINOLate) 3 Ln catalyst.…”

Section: Dedicated Cluster Communicationsmentioning

confidence: 99%

“…The core structure of 4 is reminiscent of the structures of catalytically active Zr 4 A C H T U N G T R E N N U N G (BINOLate) 6 A C H T U N G T R E N N U N G (m 3 -OH) 4 [25] and Ti 4 A C H T U N G T R E N N U N G (BINOLate) 6 A C H T U N G T R E N N U N G (m 3 -OH) 4 . [26,27] While we cannot explain the factors that give rise to the structural differences in 3 and 4, we note that the Brønsted basicities of the binaphtholate moiety are dependent on the alkali metal (ROLi < RONa < ROK). [28,29] Unlike the potassium atoms in the monomer (2), which are four coordinate, one of the potassium atoms (K2) in 4 is five coordinate, binding three THF ligands and two BINOLate oxygens (Figure 4).…”

mentioning

confidence: 96%

Characterization of Dimeric and Tetrameric μ‐Hydroxide Ytterbium(III) Binaphtholate Complexes

et al. 2007

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This manuscript is dedicated to Prof. M. Shibasaki, whose creativity and insight has changed the way we think of asymmetric Lewis acid catalysis.Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.Abstract: Shibasakis heterobimetallic Lewis acids,Ln (M = Li, Na, K and Ln = lanthanide), are an exceptionally useful class of asymmetric catalysts that exhibit high levels of enantioselectivity across a wide range of reactions. In many instances, it is necessary to add water (and base) to achieve maximum enantioselectivity. We have investigated the reaction of water withand observed formation of a novel hydroxide-bridged dimer (M = Li) and tetramer (M = K). These compounds have been characterized, including Xray structure analysis. Under anhydrous conditions, only 6-coordinate monomericYb complexes were isolated and characterized by Xray crystallography. Isolation of the dimer 4 indicates that added water can react with this important class of bifunctional catalyst to give new products. C H T U N G T R E N N U N G (m-OH) 2 and tetramer K 4 A C H T U N G T R E N N U N G (THF) 9 A C H T U N G T R E N N U N G (BINOLate) 6 Yb 4 A C H T U N G T R E N N U N G (m 3 -OH)Keywords: additives; asymmetric catalysis; bridging hydroxide; heterobimetallic catalysts; lanthanides; Lewis acidsIn the early 1990s, Shibasaki and co-workers reported the synthesis and applications of a series of heterobimetallic Lewis acid catalysts, Figure 1, M = Li, Na, K and Ln = lanthanideA C H T U N G T R E N N U N G (III)] and their 7-coordinate hydrates[1-6] These bifunctional catalysts are exceptional in their ability to catalyze a broad range of asymmetric transformations, such as the Henry reaction, [1,7] conjugate additions, [4,5,[7][8][9][10] aldol condensations, [6,11] cyanoethoxycarbonylation of aldehydes, [12] and hydrophosphonylation of aldehydes and cyclic imines, [13,14] to name a few. Despite the widespread successful application of these heterobimetallic catalysts in asymmetric synthesis, their reaction mechanisms are not well understood, because their multifunctional nature complicates mechanistic studies.

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“…38 Mikami et al described the synthesis and characterization of a tetranuclear titanium(IV)-BINOL complex as well as its application in carbonyl-ene reactions. 39,40 Recently, we described the use of a tetranuclear titanium-BINOL complex in direct aldol additions. 41 Exceptionally high regioselectivities were observed when reacting unsymmetrical ketones with enolizable aldehydes using this tetranuclear titanium-BINOL complex in direct aldol additions.…”

Section: Introductionmentioning

confidence: 99%

Multinuclear enantiopure titanium self‐assembly complexes—synthesis, characterization and application to organic synthesis

Schetter

Stosiek

Ziemer

et al. 2007

Applied Organom Chemis

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Hexa-and nonanuclear titanium complexes were obtained by self-assembly of titanium(IV)-tertbutoxide and D-mandelic acid. Suitable single crystals of these complexes were characterized by X-ray structure analysis. When used with these complexes, aldol adducts were isolated with a high degree of regioselectivity in direct aldol additions of aromatic and aliphatic aldehydes to functionalized unsymmetrical ketones. High syn-diastereoselectivities were obtained in aldol additions of enolizable aldehydes with hydroxyacetone and methoxyacetone.

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Tetranuclear titanium 7,7′‐modified binaphtholate cluster as a novel chiral Lewis acid catalyst

Cited by 40 publications

References 9 publications

Nonlinear Effects in Asymmetric Catalysis

Nonlinear Effects in Asymmetric Catalysis

Characterization of Dimeric and Tetrameric μ‐Hydroxide Ytterbium(III) Binaphtholate Complexes

Multinuclear enantiopure titanium self‐assembly complexes—synthesis, characterization and application to organic synthesis

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