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Journal Articles Journal of the American Chemical Society Year : 2013

Tunable Asymmetric Catalysis through Ligand Stacking in Chiral Rigid Rods

Abstract

Chiral benzene-1,3,5-tricarboxamide (BTA) ligands, comprising one diphenylphosphino group and one or two remote chiral 1-methylheptyl side chains, were evaluated in the rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate. Despite the fact that the rhodium atom and the chiral center(s) are separated by more than 12 covalent bonds, up to 82% ee was observed. A series of control and spectroscopic experiments confirmed that the selectivity arises from the formation of chiral helical polymers by self-association of the BTA monomers through non-covalent interactions. The addition of a phosphine-free chiral BTA, acting as a co-monomer for the chiral BTA ligands, increases the level of enantioselectivity (up to 88% ee). It illustrates how the selectivity of the reaction can be increased in a simple fashion by mixing two different BTA monomers. The concept was further probed by performing the same experiment with an achiral BTA ligand, i.e. a phosphine-functionalized BTA that contains two remote octyl side chains. It afforded an encouraging 31% ee, thus demonstrating the catalytically relevant transfer of chirality between the self-assembled units. It constitutes a unique example of the sergeants-and-soldiers principle applied to catalysis.
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hal-01696696 , version 1 (29-09-2020)

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Matthieu Raynal, François Portier, Piet W. N. M. Van Leeuwen, Laurent Bouteiller. Tunable Asymmetric Catalysis through Ligand Stacking in Chiral Rigid Rods. Journal of the American Chemical Society, 2013, 135 (47), pp.17687--17690. ⟨10.1021/ja408860s⟩. ⟨hal-01696696⟩
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