Stabilization of the N-1-substituted cytosinate iminooxo form in dinuclear palladium complexes

The synthesis, as well as chemical and structural characterization, of 1-(p-toluenesulfonyl)cytosine (1) and its dinuclear complexes of the composition Pd₂(1-TosC^?–N3,N4)₄ (3) and Pd₂(1-TosC^?–N3,N4)₂DMSO₂Cl₂ (4) by means of ESI-MS, IR, ¹H NMR and X-ray single crystal analysis are described. Ligand 1 exists in the preferred aminooxo tautomeric form, while both dinuclear complexes reveal the presence of the iminooxo form of the ligand, where 1-TosC^? stands for the anion of the cytosine derivative of 1, bridging two palladium atoms. Complex 3 has a paddlewheel structure with two square-planar coordination spheres, consisting of four N atoms each, mutually parallel and perpendicular to the interpalladium vector. Complex 4 is characterized by two mutually parallel square-planar coordination spheres consisting of two nitrogens, sulfur from the solvent molecule and a chloride. A feasible chemical route for the formation of 3 and 4 via the kinetically favoured mononuclear complex Pd(1-TosC–N3)₂Cl₂ (2) is proposed, based on the IR, ¹H NMR, mass spectrometry, elemental analysis and X-ray structure analysis data.