US EPA

3158837 

Journal Article 

Correlation between the Selectivity and the Structure of an Asymmetric Catalyst Built on a Chirally Amplified Supramolecular Helical Scaffold 

Desmarchelier, A; Caumes, X; Raynal, M; Vidal-Ferran, A; van Leeuwen, PW; Bouteiller, L 

2016 

Yes 

Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 

138 

14 

4908-4916 

English 

26998637 

10.1021/jacs.6b01306 

WOS:000374274100027 

https://www.proquest.com/docview/2000377431?accountid=171501&bdid=64576&_bd=cNE%2BX0C8M9BVoY%2BtVJiC7SX0TLo%3D
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For the first time, supramolecular helical rods composed of an achiral metal complex and a complementary enantiopure monomer provided a good level of enantioinduction in asymmetric catalysis. Mixtures containing an achiral ligand monomer (BTA(PPh2), 2 mol %) and an enantiopure ligand-free comonomer (ester BTA, 2.5 mol %), both possessing a complementary benzene-1,3,5-tricarboxamide (BTA) central unit, were investigated in combination with [Rh(cod)2]BArF (1 mol %) in the asymmetric hydrogenation of dimethyl itaconate. Notably, efficient chirality transfer occurs within the hydrogen-bonded coassemblies formed by BTA Ile and the intrinsically achiral catalytic rhodium catalyst, providing the hydrogenation product with up to 85% ee. The effect of the relative content of BTA Ile as compared to the ligand was investigated. The amount of chiral comonomer can be decreased down to one-fourth of that of the ligand without deteriorating the enantioselectivity of the reaction, while the enantioselectivity decreases for mixtures containing high amounts of BTA Ile. The nonlinear relationship between the amount of chiral comonomer and the enantioselectivity indicates that chirality amplification effects are at work in this catalytic system. Also, right-handed helical rods are formed upon co-assembly of the achiral rhodium complex of BTA(PPh2) and the enantiopure comonomer BTA Ile as confirmed by various spectroscopic and scattering techniques. Remarkably, the major enantiomer and the selectivity of the catalytic reaction are related to the handedness and the net helicity of the coassemblies, respectively. Further development of this class of catalysts built on chirally amplified helical scaffolds should contribute to the design of asymmetric catalysts operating with low amounts of chiral entities.