Alkene hydroamination with a chiral zirconium catalyst. Connecting ligand design, precatalyst structure and reactivity trends

A set of chiral bis(amidate) proligands were synthesized based on a 3,3'-substituted biphenyldiamine backbone. Zirconium precatalysts were synthesized using these proligands in situ and used for catalytic testing for intramolecular alkene hydroamination, achieving moderate enantiomeric excesses. Ligands containing electron-withdrawing substituents were found to be exceptionally reactive, in some cases catalyzing formation of pyrrolidine products at room temperature. Substitution at the 3,3'-position of the biphenyldiamine backbone was observed to significantly impact N,O-chelate binding modes, which in turn affect observed enantioselectivities. (C) 2014 Elsevier B. V. All rights reserved.