Supraphos: A supramolecular strategy to prepare bidentate ligands

Herein, we report a new strategy for the preparation of chelating bidentate ligands, which involves the mixing of two mondentate ligands functionalized with complementary binding sites. The assembly process is based on selective metal–ligand interactions employing phosphite zinc(II) porphyrins 1–6 and the nitrogen-containing phosphorus ligands b–i (Scheme 1). Only 14 monodentate ligands were utilized to generate a library of 48 palladium catalysts based on supraphos-type bidentate ligands. The characterization of rhodium complexes based on representative Supramolecular bidentate ligands and the comparison of their performance in the hydroformylation of styrene will be presented. The current library of catalysts was tested in the asymmetric palladium-catalyzed alkylation of rac-1,3-diphenyl-2-propenyl acetate, which resulted in a large variety in the observed enantioselectivity for the different catalysts. Importantly, small variations in the supraphos building blocks, lead to large differences in the enantioselectivity imposed by the catalyst, the most selective catalyst producing 97% ee.

Graphical abstractWe report a new strategy for the preparation of chelating bidentate ligands, which involves just mixing of two monodentate ligands functionalized with complementary binding sites. Phosphite zinc(II) porphyrins 1–6 and the nitrogen donor ligands b–i form a library of 60 palladium catalysts based on 48 bidentate ligands assemblies. The relatively small catalysts library gave a large variety in the selectivity of the alkylation of rac-1,3- diphenyl-2-propenyl acetate. Importantly, small variations in the building blocks lead to large differences in the enantioselectivity imposed by the catalyst (upto 97% ee).Figure optionsDownload full-size imageDownload as PowerPoint slide