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Keywords:

  • Homogeneous catalysis;
  • Hydrogenation;
  • Hydrovinylation;
  • P ligands;
  • Palladium;
  • Rhodium

Abstract

Neutral allyl–palladium complexes stabilised by bulky tris-binaphthyl monophosphite ligands have been prepared and fully characterised in solution by NMR spectroscopy, which evidenced a dynamic equilibrium between two diastereomeric species. The new allyl–palladium phosphite complexes have been evaluated as catalytic precursors in the asymmetric hydrovinylation of styrene; they show moderate activity and good to excellent chemo- and enantioselectivity depending on the substituent at the ligand 2′-binaphthyl position. Remarkably, the palladium complex bearing the ligand with an adamantyl ester substituent led to 92 % ee toward (R)-3-phenyl-1-butene, which suggests that the ester functionality might provide a secondary hemilabile interaction with the metal, thus favouring the enantioselectivity control. Rhodium(I) complexes formed in situ with the same ligands were further applied in the hydrogenation of dimethyl itaconate, but gave limited activity. The best enantioselectivity (62 %) was achieved with the same ligand that contained the adamantyl ester substituent.