Substituent Effects of β-Diketiminate Ligands on the Structure and Physicochemical Properties of Copper(II) Complexes

Substituent effects of β-diketiminate ligands on the structure and physicochemical properties of the copper(II)
complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R3NCHC(R1)CHNHR3, where R1 is Me, H, CN, or NO2, and R3 is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp
(2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R3 = Ph or Dtbp were treated with
CuII(OAc)2, bis(β-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the
crystal structures of which were nearly the same as each other regardless of the α-substituent (R1); dihedral
angles between the two β-diketiminate coordination planes are 62.5 ± 1.2°, and the Cu−N bond lengths are 1.959
± 0.008 Å. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially
g∥ values of the ESR spectra and the d−d bands of the absorption spectra, as well as the electrochemical behaviors
of the complexes, are significantly affected by the electronic nature of R1. The ligands with R3 = Mes and Dep,
on the other hand, gave di(μ-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic
and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered
aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported
by one β-diketiminate ligand and one didentate acetate ion. Thus, the β-diketiminate ligands with a variety of
substituents (R1 and R3) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear
and dinuclear copper(II) complexes with significantly different coordination geometry and properties.