Ligand design for Rh(I)-catalyzed hydroformylation and Pd-catalyzed asymmetric allylic alkylation

Abstract

The development of Briphos ligand enables highly active and regioselective hydroformylation. Especially, direct hydroformylation of trisubstituted olefins has been achieved with a combination of a Rh(I) catalyst and a π–acceptor phosphorus (briphos) ligand. A sterically bulky briphos ligand with a large cone angle that forms a 1:1 complex with Rh(I) is found to be reactive for the hydroformylation of tri-substituted olefins. The aldehyde products were obtained with high diastereoselectivity (>99:1) and regioselectivity (49-81%). Moreover, development of a highly active and enhanced stability of catalyst has been achieved through synergistic ligand effect between PPh3 and Briphos ligands in the hydroformylation of propylene. Our optimal briphos ligand exhibit superior reactivity of 16,500 h$^{-1}$ as turnover frequency with high iso-butyraldehyde selectivity of 0.84. In addition, the catalyst activity was increased to 22,000 h$^{-1}$ as turnover frequency by adding one equivalent of PPh3 compared to rhodium catalyst. Notably, synergistic ligand effect between PPh3 and briphos ligand was observed in the aspect of both catalytic activity and stability. In addition, chiral bicyclic bridgehead phosphoramidite(briphos) prepared from (R,R)-1,2-diaminocyclohexane with 2-diphenylphosphino benzoic acid is highly efficient and selective ligand for palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate. Compared to trost ligand, we confirmed that briphos ligand clearly forms 1:1 palladium complex with 1,3-diphenyl allylic substrate and crystal structure also obtained. Briphos ligand is proven to be an effective method in palladium catalyzed allylic alkylation with various carbon nucleophiles showing good reactivity(74-98%), enantioselectivity(78-99% ee) and diastereoselectivity(dr = 6.7).