Chiral nickel(II) and palladium(II) NCN-pincer complexes based on substituted benzene: Synthesis, structure, and lewis acidity

Air- and moisture-stable nickel(II) and palladium(II) complexes from phebox pincer ligands 1-5 have been synthesized, and their Lewis activity was investigated. 2,6-Bis(oxazolinyl)phenylnickel halide complexes [NiX(phebox)] and 2,6-bis(oxazolinyl)phenylpalladium halide complexes [PdX(phebox)] were synthesized via oxidative addition with [Ni(COD)2] or Pd(2)dba(3), respectively, followed by halide abstraction using silver(l) salts to form complexes such as [Ni(phebox)][ClO(4)] (41). Herein, X-ray crystal structures are reported for several pincer complexes having the expected square-planar geometries with the terdentate NCN pincer system. Complexes with general structure [M(phebox)]X where X is a halogen showed no relative Lewis acidity. On the other hand, complexes where X was exchanged for a less coordinating counterion showed increased Lewis acidity. The relative Lewis acidity varies depending on the substituents on the benzene core of the pincer ligands, due to the electronic effects of the ligand on the metal center.