Thermally Stable P‐Chiral Supramolecular Phosphines, their Self‐Assembly and Implication in Rh‐Catalyzed Asymmetric Hydrogenation

Abstract

AbstractP‐chiral supramolecular phosphine ligands are crucial for asymmetric transformations, but their synthesis is tedious. We report a one‐step synthesis of thermally stable P‐chiral supramolecular phosphines and their performance in the asymmetric hydrogenation of functionalized alkenes. A rational designing and synthesis of (R, R)‐QuinoxP* ligated palladium complex (Pd‐2) in excellent yield is reported. This Pd‐2 catalyzed a direct P−C coupling of 2,3‐dihydro‐1‐H‐phosphindole (A1)/1,2,3,4‐tetrahydrophosphindoline (A2) with 1‐(3‐iodophenyl)urea (B1)/2‐iodo /6‐hydroxy pyridine (B2) and,produced corresponding ligands L1–L3. The P−C coupling between A1 and B2 produced 6‐(2,3‐dihydro‐1H‐phosphindol‐1‐yl)pyridine‐2(1H)‐one (L2) with an excellent enantiomeric excess of up to 99 %. L2 was found to be remarkably stable even at 150 °C and did not oxidize/hydrolyze for at least 24 hours in open air. Such thermal stability and an impediment to oxidation are unprecedented. L2 self‐assembled and produced L2−C1 (Pt), L2−C2(Pd), and L2−C3(Rh) assemblies. The utility of the self‐assembled P‐chiral ligand was demonstrated in the Rh‐catalyzed asymmetric hydrogenation (AH) of functionalized olefins. The L2−C3 catalyzed AH of functionalized alkenes and delivered chiral products with excellent enantioselectivity of >99 %. A small library of 16 substrates was subjected to AH using L2−C3 to produce chiral compounds with excellent conversion and ee.