1H NMR spectra of ternary platinum(II) complexes with N-ethyl- or N- benzyl-1,2-ethanediamine and 2,2'-bipyridine or 1,10-phenanthroline: Intramolecular aromatic-aromatic interaction in coordination sphere, and it's solvent and temperature effects

Article abstract of DOI:10.1246/bcsj.73.1589

Square-planar complexes with the formula [Pt(L₁) (L₂)]X₂, where L₁ is di(ammine) or 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) and L₂ is N-ethyl-1,2-ethanediamine (Eten) or N-benzyl-1,2-ethanediamine (Been), and X = NO₃^- or Cl^-, were prepared. NMR measurements of D₂O solutions of these complexes showed that the N-ethyl and N-benzyl groups are forced to take a pseudo axial disposition due to an intramolecular repulsion from hydrogen atoms of aromatic diamines for complexes where L₁ = bpy or phen and significant upfield shifts due to the ring current effect were observed for the Been complexes. An analysis of coupling with N-H and ¹⁹⁵Pt showed that the major rotamer due to rotation around CH₂-NH is (-)-syn for the Been with a significant intramolecular stacking between aromatic rings of L₁ and L₂, but anti-for the Eten complexes. The solvent and temperature dependency of the upfield shift of the Been complexes are described; the protein denaturants, guanidinium chloride, and urea, act to reduce stacking as dioxane.