Palladium catalytic species containing chiral phosphites: Towards a discrimination between molecular and colloidal catalysts

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.