Enantiopure bisphosphine ligands with appended crown ether groups as regulation sites for Rh-mediated hydrogenations

Herein is reported the efficient preparation of a set of enantiopure bisphosphine ligands, whose backbone incorporates an array of diverse crown ethers as distal regulation sites via well-defined supramolecular interactions to tune the catalytic properties of the bisphosphine groups. These new ligands enabled very good catalytic activity in rhodium-mediated asymmetric hydrogenations at low catalyst loadings, while the enantioselectivity remained moderate. Slightly positive regulation effects for the enantioselectivity of the hydrogenation reactions were obtained as a result of the combination of the appropriate bisphosphine ligand and different regulation agents.