No abstract

Stereodynamic ligands and complexes bearing functional groups to attach chiral or achiral binding sites and auxiliaries are highly attractive due to the interesting opportunities for controlling the stereochemical outcome of enantioselective transformations. In this study we report the preparation of a 3,3'-functionalized biphenol (BIPOL) phosphoramidite ligand (P ) bearing 3,5-dichlorobenzoyl (3,5-DCB) amide binding sites for noncovalent interactions. Upon coordination to [Rh(COD) ]BF this substitution pattern directs one of the 3,5-DCB binding sites in close proximity of the metal center resulting in liberation of both COD ligands and the formation of a [Rh(P ) ]BF complex. Coordination of the amide carbonyl unit was found to be reversible, since the complex acted as an active catalyst in the hydrogenation of dehydroamino acid derivatives. X-ray crystallographic investigation revealed that the second 3,5-DCB unit is capable of forming noncovalent π-π interactions connecting both phosphoramidite ligands.

141 (1925).

Novel L-tartaric acid based stereodynamic biphenylbisphosphinite ligands with anilino linkers were prepared as cyclic diamide compounds. The influence of the constitutional substitution pattern of the amino group at the aniline moiety on the diastereoselective formation of the ligand was investigated. While the meta-anilino bridged ligands showed a highly dynamic behavior and no discrimination between (R ax ) and (S ax ) configuration, L-tartaric acid substitution on ortho-anilino bridged ligands leads to diastereoselective self-alignment of the central biphenol axis, which controls the stereoselectivity of the ligand and catalyst. The experimental findings were corroborated by theoretical calculations. In the rhodium-catalyzed enantioselective hydrogenation of methyl 2acetamidoacrylate (MAA), an enantiomeric ratio of 75 : 25 (R/S) was obtained for the ortho-substituted ligand.