Heterogeneous Asymmetric Catalysis in Water with Amphiphilic Polymer-Supported Homochiral Palladium Complexes

Heterogeneous aquacatalytic highly selective organic transformations are what may be considered ideal chemical processes of the next generation, where the advantages of both aqueous- and heterogeneous-switching are combined in one system to meet green sustainable chemical requirements. Heterogeneous aquacatalytic asymmetric reactions were achieved with palladium complexes of homochiral phosphine ligands which were immobilized onto amphiphilic polystyrene–poly(ethylene glycol) (PS–PEG) resin beads via chemical bonding. The catalyst was recovered by simple filtration and was reused without any loss of catalytic activity and stereoselectivity. In particular, a novel chiral P,N-ligand, (3R,9aS)-2-aryl-3-[2-(diphenylphosphino)phenyl]tetrahydro-1H-imidazo[1,5-a]indole-1-one, was designed and prepared on PS–PEG to realize palladium-catalyzed π-allylic substitution of both cyclic and acyclic substrates with carbon, nitrogen, and oxygen nucleophiles in water with enantioselectivity of up to 99% ee.