Structural Investigations on Enantiopure POP Ligands: a High- Performing POP Ligand for Rhodium-catalysed Hydrogenations

Abstract

A second generation of phosphine–phosphite (P–OP) ligands, incorporating a more sterically bulky phosphite group than previous P–OP ligand designs, gave very efficient catalysts for the Rh‐catalysed asymmetric hydrogenation of a diverse array of substrates (11 examples, 93–99 % ee) containing structurally diverse substituents and chelating groups at the C=C double bond. The presence of the sterically bulky (Sa)‐3,3′‐diphenyl‐5,5′,6,6′,7,7′,8,8′‐octahydro‐[1,1′‐binaphthalene]‐2,2′‐diol‐derived phosphite fragment caused significant increases in enantioselectivity (up to Δee = 58 %), and provided improved results compared to those obtained with the first generation of P–OP‐derived rhodium catalysts {i.e., rhodium complexes incorporating phosphine–phosphite ligands with (Ra)‐ and (Sa)‐BINOL‐derived phosphite groups; BINOL = [1,1′‐binaphthalene]‐2,2′‐diol}. Overall, the optimal ligand L8 provided very high enantioselectivities for a range of structurally diverse olefins (up to 99 % ee).