Versatile Syntheses of Optically Pure PCE Pincer Ligands: Facile Modifications of the Pendant Arms and Ligand Backbones

A series of chiral C-stereogenic
PCP and PCN ligand precursors
were prepared in situ from inexpensive achiral starting materials
via a simple catalytic asymmetric P–H addition reaction in
good overall yields. This facile catalytic method of preparing the
ligand backbones renders easy and economical modifications of the
electronically crucial para-substituent, chiral functionalities,
and donor atoms for different transition metal ions. A one-pot synthetic
procedure was used efficiently to prepare the corresponding optically
pure pincer complexes. All the new complexes were characterized by
NMR and mass spectroscopy. The molecular structures of several selected
complexes have also been elucidated by X-ray crystallography. Preliminary
studies indicated that minor structural changes on these novel pincer
complexes affect their chemical properties significantly when they
were applied as catalysts for the reaction between diphenylphosphine
and chalcone.