¹H-NMR Study of Ternary Platinum(II) Complexes with N-(1-Naphtyl)methyl-1,2-ethanediamine or N-(9-Anthrylmethyl)-1,2-ethanediamine and Bipyridine or Phenanthroline and Restricted Single Bond Rotation Due to Aromatic–Aromatic Ring Interaction

Abstract

¹H-NMR spectra of square-planar complexes with the formula [Pt(L¹)(L²)]X₂ where L¹ is 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L² is N-(1-naphthyl)methyl-1,2-ethanediamine (Npen) or N-(9-anthryl)methyl-1,2-ethanediamine (Aten) indicate that the N-naphthylmethyl and N-anthrylmethyl groups are forced to adopt a pseudo axial disposition due to intramolecular repulsion of hydrogen atoms of the aromatic diimines. The aromatic–aromatic interactions in the N-arylmethyl-1,2-ethanediamine complexes and aromatic diimines caused them to undergo intramolecular stacking. ¹H-NMR spectra of these complexes showed a significant concentration and temperature dependence. The monomer–dimer equilibrium was estimated, based on the concentration dependency. Restricted single bond rotation was estimated from temperature dependency data. The rotation of the anthracene ring of the [Pt(bpy)(Aten)]²⁺ complex showed an activation energy of ca. 38 kJ mol⁻¹, which is in good agreement with a mechanism involving successive rotations about single bonds with restriction by intramolecular aromatic–aromatic ring interactions.