Accelerated and Enantioselective Synthesis of a Library of P-Stereogenic Urea Phosphines

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

P-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.

Ni-Catalyzed Asymmetric Hydrophosphination of Unactivated Alkynes

The practical synthesis of P-stereogenic tertiary phosphines, which have wide applications in asymmetric catalysis, materials, and pharmaceutical chemistry, represents a significant challenge. A regio- and enantioselective hydrophosphination using cheap and ubiquitous alkynes catalyzed by a nickel complex was designed, in which the toxic and air-sensitive secondary phosphines were prepared in situ from bench-stable secondary phosphine oxides. This methodology has been demonstrated with unprecedented substrate scope and functional group compatibility to afford electronically and structurally diversified P(III) compounds. The products could be easily converted into various precursors of bidentate ligands and organocatalysts, as well as a variety of transition-metal complexes containing both P- and metal-stereogenic centers.

Phosphorus Ligands in Hydroformylation and Hydrogenation: A Personal Account

Metal-catalyzed hydroformylation and hydrogenation heavily rely on ligands, among which phosphorous ligands play a pivotal role. This personal account presents a selection of three distinct classes of phosphorous ligands, namely, monodentate meta-substituted phosphinites, bis-phosphites, and P-chiral supramolecular phosphines, developed in our group. The synthesis of these ligands, isolation, characterization, and their performance in transition metal-catalyzed hydroformylation, isomerizing hydroformylation, and asymmetric hydrogenation of olefins is summarized. The state of the art development in iron-catalyzed hydroformylation of alkenes and our contributions to the field is discussed. Use of phosphines enabled iron-catalyzed hydroformylation of alkenes under mild conditions. Thus, this account demonstrates the central role of phosphorus ligands in industrially relevant transformations such as hydrogenation and hydroformylation. The seemingly matured field of ligand discovery still holds significant potential and will steer the field of homogeneous catalysis.

Synthesis of P-chiral phosphine compounds by palladium-catalyzed C–P coupling reactions

An efficient C–P coupling reactions of enantiopure tert-butylmethylphosphine-boranes with aryl and heteroaryl halides is developed by using Pd(OAc)₂/dppf as a catalyst, affording a series of P-chiral phosphines (up to 99% ee).