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Keywords:

  • Tautomerism;
  • Rhodium;
  • Hydrogenation;
  • Phosphorus;
  • Chirality

Abstract

P-chirogenic, supramolecular hydrogen-bonding C1-symmetrical sulfonamido–phosphinamides (METAMORPhos) have been successfully prepared. They were all found to possess a characteristic prototropic equilibrium between the PIII and the PV tautomers that is slow on the NMR spectroscopic timescale. Despite the dynamic and reversible protonation of the P centre, the P-chirogenic information was found to be retained in the tautomerization process, even in a protic solvent environment. Several strategies to access the corresponding enantiopure compounds were investigated, such as diastereoselective crystallization, or enantioselective synthesis. It was possible to resolve such a class of chiral ligands with up to 99 % ee, and apply them in the Rh-catalyzed asymmetric hydrogenation of alkenes. These ligands are interesting new building blocks in the area of acid/base-type noninnocent ligand catalysis.