Selective binding of benzenediol derivatives by simultaneous non-covalent interactions in bis-Pt(II) aza-aromatic host–guest system

Abstract

We have designed and synthesized a new ligand, 6-(2-pyridinyl)-4-[3′-(3-pyridinyl)[1,1′-biphenyl]-3-yl]-2,2′-bipyridine (2). 2 reacted with Pt(cod)(MeCN)₂(BF₄)₂ to quantitatively give the molecular dimer, 1·BF₄ (2₂·Pt^II₂·4BF₄⁻), by self-assembly. The ¹H NMR and UV-vis titration showed that the complexation affinity of 1·BF₄ toward benzenediol guests decreases in the order para > meta > ortho. The structural analysis revealed that the π-π stacking interactions and multiple CH⋯O hydrogen bonds make the benzenediol binding favorable. DFT calculations showed that complexation with Pt(II) leads to a unique charge distribution in 1 creating more positive sites inside the cavity that provides a strong binding site for benzenediols. The macrocyclic preorganization effect, induced-fit complexation mechanism, Coulombic interactions, such as π-π stacking interactions, and CH⋯O hydrogen bonding contribute to the benzenediol recognition.