292865-89-5

Upstream product

• 32305-98-9 (-)-Diop 

Relevant academic research and scientific papers

Immobilization of chiral cationic diphosphine rhodium complexes in nanopores of mesoporous silica and application in asymmetric hydrogenation

Heterogeneous chiral cationic rhodium complexes bearing bidentate phosphine derived from (-)-2,2-dimethyl-4,5-bis(diphenylphosphino)methyl)-1,3-dioxolane (DIOP) were prepared by covalent immobilization onto SBA type silica. In order to introduce the tether to the surface, it was necessary to modify chemically the DIOP ligand through a reaction sequence consisting of hydrolysis and condensation with organosiloxane precursor. Two types of cationic rhodium hybrid materials based on SBA-15 and partially capped SBA-3 type silica were prepared under classical grafting procedures. The catalytic solids were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. The performances of these latter were then evaluated in the hydrogenation of methyl (Z)-2-N-acetylaminocinnamate under various reaction conditions (pressure and temperature). Generally, the activity of supported catalysts was high as full conversions were obtained but immobilization of the system leads to significant loss of enantioselectivity. The best ee (20%) was observed in the case of the catalyst whose surface had been passivated prior to the grafting but the enantiomeric excesses were fairly below the values of the homogeneous catalysis.

Cooperative attractive interactions in asymmetric hydrogenations with dihydroxydiphosphine Rh(I) catalysts - A competition study

Studies for controlling rate and enantioselectivity of the asymmetric hydrogenation with Rh-diphosphine catalysts by cooperative attractive interactions within the framework of catalyst-substrate complexes are represented. In strong contrast to a Rh(I)[threo-1,4-bis(diphenylphosphino)butane-2,3-diol] catalyst an extremely fast reaction took place applying the complex of the analogue erythro ligand. This is likely due to a strong intramolecular hydrogen bond between the vicinal HO groups impeding the hemilabile coordination of one of the hydroxy groups on the metal center during the hydrogenation. When a substrate with strong hydrogen bond acceptor properties such as (E)-methyl 3-dimethoxyphosphorylbut-2-enoate was hydrogenated even the threo catalyst exhibited a fast reaction. The product was obtained in 83% ee. In contrast, when in the ligand both HO groups were replaced by MeO groups only poor conversion and 24% ee were achieved. While with the complex bearing HO groups in methanolic solution the corresponding diastereomeric catalyst substrate complexes were dominant, analogue MeO groups bearing catalyst substrate complexes could not be detected by NMR. For the latter, only the Rh(I)-solvent complex was found revealing the high importance of the additional functional groups on this equilibrium.