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Diastereospecific Coupling of Imines by Low-Valent Titanium: An Experimental and Computational Study

Kumar, Akshai and Samuelson, Ashoka G (2011) Diastereospecific Coupling of Imines by Low-Valent Titanium: An Experimental and Computational Study. In: European Journal of Organic Chemistry (5). pp. 951-959.

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Official URL: http://onlinelibrary.wiley.com/doi/10.1002/ejoc.20...

Abstract

The reaction of phenylsilane (PhSiH3) and titanium(IV) isopropoxide Ti(OiPr)(4)] generates low-valent titanium alkoxides that reduce and reductively couple imines. The C-C coupling reaction is diastereospecific, with exclusive formation of the (+/-)-isomer. The yield is dependent on the concentration of titanium(IV) isopropoxide used. Using imines with varying electronic demand revealed that the coupling is most efficient for unsubstituted imines. The involvement of a trimeric titanium biradical species is invoked to explain the observed concentration dependence and diastereospecificity in the reaction. Multilayer ONIOM (''our own n-layered integrated molecular orbital and molecular mechanics'') calculations were carried out on the plausible intermediates involved by using the Guassian 09 suite of programs. Formation of the trimeric biradical species leading to the formation of the (+/-)-isomer is more favored than formation of the trimeric biradical species, which leads to the meso-isomer. Similar calculations with dimeric intermediates do not predict the (+/-)-selectivity. Mass spectral analysis of the reaction mixture indicates the presence of a trimeric titanium alkoxide species.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to John Wiley and Sons.
Keywords: Titanium; Diastereoselectivity; Transition states; Reduction; Amines
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: Id for Latest eprints
Date Deposited: 24 Mar 2011 06:31
Last Modified: 24 Mar 2011 06:31
URI: http://eprints.iisc.ac.in/id/eprint/36205

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