Recent Advances in Supramolecular Chirality Sensing and Enantiodifferentiating Heterogeneous Catalysis

Optically active compounds are the key elements in biological systems. Therefore, the absolute configuration determination and manifacture of chiral substances have attracted much attention due to its direct relevance to many natural processes and important implications in various fields, such as chiroptical devices, sensors, modern molecular and supramolecular technologies, and pharmaceuticals.

In relation to these problems, we have designed a powerful tool for the determination of absolute configuration on the basis of smart combination of supramolecular chemistry and chiroptical methodology. In particular, it was found that simple achiral ethane-bridged bis-porphyrin hosts (1) are able to effectively sense chirality of various enantiomeric guests via formation of the stable 1:2 supramolecular chiral complexes and induction of the noticeable (moderate-to-strong) exciton couplet circular dichroism (CD) signals in the absorption region of 1.^1-6 The generated CD sign unambiguously correlates with the induced helicity allowing straightforward determination of the absolute configuration of various chiral guests and thus making it possible to apply 1as effective and universal chirality sensors for different types of optically active compounds as in solution and in the solid state. Furthermore, to expand chiroptical applicability some chiral thin films have been obtained on the basis of these supramolecular systems.

To solve the second problem, i.e. effective production of optically active compounds, we have developed new supramolecular heterogeneous enantiodifferentiating catalysts for the asymmetric hydrogenation of prochiral ketones.^7-10These chiral catalysts can be easily prepared by treating the surface of metallic nickel with the solution of enantiopure tartaric acid (TA) and the auxiliary modifier (NaBr). Whilst the role of metallic nickel is to drive the hydrogenation reactions itself, the adsorbed TA provides the supramolecular asymmetric environment for differentiating the corresponding enantioface of prochiral substrates. These catalysts possess a superior efficiency, hence exhibiting the enantio-selectivity of up to 96% and the conversion of up to 100% in the case of alkyl acetoacetates. Furthermore, this material is highly robust and stable maintaining a remarkably high hydrogenation activity and enantio-differentiating ability for ca. 3 months under the certain conditions of storage, which opens up considerable promise for the industrial application. Further details and implications towards these research fields will be presented and discussed.

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