Synthesis of P-Chiral Phosphanes from Low-Coordinate Phosphorus Compounds as Bidentate Ligands in Stereoselective Catalysis

• Applicants: Professorin Dr. Evamarie Hey-Hawkins; Professor Dr. Johannes Gerardus de Vries, since 2/2021
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411421782

Chiral phosphanes are an important class of ligands in asymmetric synthesis and catalysis. Most compounds exhibit a C-chiral backbone. P-chiral ligands are far less common, and this is mainly attributed to their difficult synthetic access. Asymmetric phospha-Diels–Alder reaction of 2H-phospholes with suitable dienophiles (employing the principle of differentiation of stereotopic faces) yields P-chiral cyclic phosphanes in a facile and low-cost procedure. The highly diastereoselective course of the cycloaddition reaction facilitates efficient access to stereochemically complex heterocyclic structures. Cleavage and addition reactions of the resulting phosphanorbornenes will be employed to prepare a diverse range of novel phosphorus heterocycles based on a chiral 1-phosphanornbornane fragment, which are valuable starting materials for the development of novel bidentate P-chiral ligands.An analogous phospha-aza–Diels-Alder reaction of 2H-phospholes with suitable imines will be carried out for the preparation of enantiomerically pure 1-phospha-2-azanorbornenes. Cleavage of the reactive P–N bond of these heterocycles, especially by chiral reagents (Grignard reagents, alcohols, amines), will be employed for the synthesis of chiral bidentate P,N ligands based on a 2,3-dihydrophosphole framework.These readily accessible and easily modifiable chiral, potentially bidentate ligands with 1-phosphanorbornane or 2,3-dihydrophosphole frameworks will be employed in catalytic reactions. These will include palladium-catalysed asymmetric Suzuki-Miyaura coupling and asymmetric allylic substitution reactions, rhodium-catalysed asymmetric hydroformylation of alkenes, asymmetric transferhydrogenation, asymmetric oxa-Michael reactions using novel ruthenium-pincer complexes and asymmetric hydrogenation of ketones. In addition, molecular modelling of the transition states of these catalytic reactions will be performed to get a better understanding of the influence of the P-chiral ligands on the expected selectivities and activities of hydrogenation reactions.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Paul C. J. Kamer, until 2/2021 (†)