Enantiopure narrow bite-angle P-OP ligands: synthesis and catalytic performance in asymmetric hydroformylations and
Héctor Fernández-Pérez1, Jordi Benet-Buchholz, Anton Vidal-Ferran
1Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona (Spain), Fax: (+34) 977920228.
Abstract:
Herein is reported the preparation of a set of narrow bite-angle P-OP ligands the backbone of which contains a stereogenic carbon atom. The synthesis was based on a Corey-Bakshi-Shibata (CBS)-catalyzed asymmetric reduction of phosphomides. The structure of the resulting 1,1-P-OP ligands, which was selectively tuned through adequate combination of the configuration of the stereogenic carbon atom, its substituent, and the phosphite fragment, proved crucial for providing a rigid environment around the metal center, as evidenced by X-ray crystallography. These new ligands enabled very good catalytic properties in the Rh-mediated enantioselective hydrogenation and hydroformylation of challenging and model substrates (up to 99 % ee). Whereas for asymmetric hydrogenation the optimal P-OP ligand depended on the substrate, for hydroformylation, a single ligand was the highest-performing one for almost all studied substrates: it contains an R-configured stereogenic carbon atom between the two phosphorus ligating groups, and an S-configured 3,3'-diphenyl-substituted biaryl unit.
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