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. © 2008 Pharmaceutical Society of Japan.