Dinuclear nucleobase-anion-bridged complexes of PdII and PtII with 1-methylimidazol-2-yl pyridin-2-yl ketone: synthesis, crystal structure and solution behaviour

Abstract

The reactions of [M(mipk)(H₂O)₂]²⁺(M = Pd or Pt; mipk = 1-methylimidazol-2-yl pyridin-2-yl ketone) with the nucleobases 1-methylthymine (Hmthy) and 1-methyluracil (Hmura) were studied and the products characterized by X-ray structure analyses as well as by ¹H NMR spectroscopy. Dinuclear complexes are formed with the pyrimidine-based model nucleobases, which act as secondary bridging ligands via their N³ and O⁴ donor functions. In all three compounds [Pd₂(mipk)₂(mura)₂][ClO₄]₂1, [Pd₂(mipk)₂(mthy)₂][ClO₄]₂2 and the isotypic compound [Pt₂(mipk)₂(mthy)₂][ClO₄]₂3 the nucleobases show head-to-tail arrangement. The intramolecular M ⋯ M distances vary from 2.861(1)Å in 2 to 2.879(1)Å in 1. By ligand-exchange reaction in aqueous media the side product [Pt(mipk)₂][ClO₄]₂ is formed. Proton NMR studies showed that the dinuclear complexes are not stable in aqueous solution. Oxidation of 3 and [Pt₂(mipk)₂(mura)₂][ClO₄]₂4 to platinum blues with higher-valent Pt was not observed. Presumably this is due to the competing oxidation of the low-potential mipk ligand.