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Shibasaki catalysts constitute a class of hetero-bimetallic complexes with the general formula n(binol)3(M)3.html" ;"title="binol.html" ;"title="n(binol">n(binol)3(M)3">binol.html" ;"title="n(binol">n(binol)3(M)3(M = alkali metal, Ln = lanthanide). They are named after Masakatsu Shibasaki, whose group first developed them, and are used as asymmetric catalysis, asymmetric catalysts.
Shibasaki catalysts constitute a class of hetero-bimetallic complexes with the general formula n(binol)3(M)3.html" ;"title="binol.html" ;"title="n(binol">n(binol)3(M)3">binol.html" ;"title="n(binol">n(binol)3(M)3(M = alkali metal, Ln = lanthanide). They are named after Masakatsu Shibasaki, whose group first developed them, and are used as asymmetric catalysis, asymmetric catalysts.
Development
The Shibasaki group produced the first chiral lanthanide-binaphtholate complex in 1992, which was used to catalysenitroaldol reaction
The Henry reaction is a classic carbon–carbon bond formation reaction in organic chemistry. Discovered in 1895 by the Belgian chemist Louis Henry (1834–1913), it is the combination of a nitroalkane and an aldehyde or ketone in the presence ...
s. The complex was not characterised but was the first to perform the reaction enantioselectively.
This success led to further research which resulted in the development of heterometallic complexes with the formula n(binol)3(M)3 the structure of which was elucidated by X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
.
Scope
Shibasaki catalysts are effective for a wide range ofenantioselective
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...
reactions including nitroaldol, Michael, Diels-Alder and hydrophosphonylation reactions.
Their effectiveness arises in part from their ability to act as both a Brønsted base by virtue of the metal alkoxide and a Lewis acid via the lanthanide ion. Enantioselectivity has been found to be sensitive to both Ln and M; with the nitroaldol reaction being most effective when Ln = Eu and M = Li
whereas the Michael reaction requires Ln = La and M = Na. It was observed that alterations of Ln and M caused predictable changes in the bite angle
In coordination chemistry the bite angle is the ligand–metal–ligand bond angle of coordination complex containing a bidentate ligand. This geometric parameter is used to classify chelating ligands, including those in organometallic complexes ...
of the binaphthol backbone.
References
{{Reflist Catalysts