title: 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 noncovalent interactions. The addition of a phosphine-free chiral BTA, acting as a comonomer 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.
authors.affiliation: UPMC Univ Paris 06 , UMR 7610, Chimie des Polymères, F-75005 Paris, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Raynal
authors.forename: François
authors.initials: F
authors.lastname: Portier
authors.forename: Piet W N M
authors.initials: PW
authors.lastname: van Leeuwen
authors.forename: Laurent
authors.initials: L
authors.lastname: Bouteiller
mesh_terms: D001549:Benzamides / Q000737:chemistry*; D002384:Catalysis; D006865:Hydrogenation; D008024:Ligands; D010720:Phosphines / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*; D013386:Succinates / Q000737:chemistry*
chemical_list: D001549:Benzamides; D008024:Ligands; D010720:Phosphines; D013386:Succinates; C558700:benzene-1,3,5-tricarboxamide; C518953:dimethyl itaconate; D012238:Rhodium; C044646:phosphine