Mechanism and Enantioselectivity of [Zinc(diamine)(diol)]-Catalyzed Asymmetric Hydrosilylation of Ketones: DFT, NMR and ECD Studies

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Abstract

NMR and ECD measurements together with density functional theory computations were used to analyze the mechanism of [Zn(diamine)(diol)]-catalyzed ketone hydrosilylation. Of the three possible pathways, the one that assumes formation of a Zn-hydride species acting as an active catalyst appears energetically most favorable. This conclusion is in contrast to a previously proposed mechanism that assumed the reaction between the [Zn(diamine)(diol)] catalyst, the silane, and the substrate, took place through Zn-activation of the carbonyl group. The absolute stereochemistry of the final product predicted on the basis of our proposal is in agreement with the available experimental data. It appears that the most important factor that controls stereochemistry of the whole process is preorganization of the reaction substrates by formation of a NH···O=C hydrogen bond between the catalyst and the substrate.

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