Palladium Catalytic Species Containing Chiral Phosphites: Towards a Discrimination between Molecular and Colloidal Catalysts
Résumé
Palladium nanoparticles (Pd1–Pd3) stabilized by chiral diphosphite ligands (1–3), were synthesized and tested as catalysts for the allylic alkylation reaction, using different substrates (rac‐I, rac‐III and rac‐V). Carbohydrate ligands (1 and 2), only differing in the C‐3 configuration, led to a remarkable difference in stability of the corresponding nanoparticles: while Pd1 is a robust catalyst, Pd2 decomposes into molecular species. In addition, the high enantioselective systems, Pd1 and Pd3, are only active for a substrate containing phenyl groups. Concerning the catalytic behaviour of the corresponding molecular systems, palladium complexes coordinated to ligands 1 or 3, gave excellent asymmetric inductions, but an analogous catalyst accommodating ligand 2, was not found selective.