Syntheses, Spectroscopy, and Structural Analyses of Dinuclear Chiral‐at‐Metal μ‐Aqua‐tetrakis[(<i>R</i> or <i>S</i>)‐<i>N</i>‐1‐(Ar)ethylsalicylaldiminato]di‐Λ‐ or ‐Δ‐nickel(II) Complexes

Abstract

Abstract Enantiopure dinuclear μ‐aqua‐tetrakis[( R or S )‐ N ‐1‐(Ar)ethylsalicylaldiminato]di‐Λ‐ or ‐Δ‐nickel(II) [Ar = C 6 H 5 ( R ‐ 1 / S ‐ 1 ), p ‐MeOC 6 H 4 ( R ‐ 2 / S ‐ 2 ), p ‐ClC 6 H 4 ( R ‐ 3 / S ‐ 3 ), p ‐BrC 6 H 4 ( R ‐ 4 )] complexes have been synthesized from the reaction between ( R or S )‐ N ‐1‐(Ar)ethylsalicylaldimine and nickel(II) acetate. Their CD spectra demonstrate chirality transfer from the ligands to the metal ions and a mirror‐image relationship for the enantiomeric pair R ‐ 3 / S ‐ 3 in thf. DSC analyses show that the complexes exhibit an irreversible dissociation to the mononuclear species, which in turn undergo decomposition. The 1 H NMR spectra reveal the presence of four salicylaldiminates, one aqua ligand, and two molecules of methanol in each dinuclear complex. They also confirm the existence of a dinuclear‐bridged aqua bis‐octahedral Ni II complex in solution. The IR spectra in CH 2 Cl 2 show a very strong band at around 2306 cm –1 due to the νO–H of the bridged aqua ligand. The X‐ray structures of R ‐ 2 , S ‐ 2 , R ‐ 3 , and S ‐ 3 confirm the formation of dinuclear compounds comprising two nickel ions, four salicylaldiminates, and one aqua ligand with two molecules of methanol (or water in S ‐ 2 ). Each nickel ion is surrounded by two N , O ‐chelating salicylaldiminates, a bridging salicyl‐O atom from the neighboring nickel ion, and a bridging aqua ligand in a distorted octahedral polyhedron. Analyses of the absolute structures reveal a diastereomeric induction of the R or S ligand giving a Λ or Δ configuration at the nickel atoms in R ‐ 2 / 3 or S ‐ 2 / 3 that is independent of the ligand substituents.