N1-Coordination in palladium(II) and platinum(II) complexes with 9-methylhypoxanthine: crystal structures and theoretical calculations

Abstract

The synthesis of the new palladium and platinum complexes with 9-methylhypoxanthine (9-mhypH) of the type [M(dmba)(L)(9-mhypH-N7)]ClO₄ [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl; M = Pd or Pt; L = DMSO, PPh₃ or PTA (PTA = 1,3,5-Triaza-7-phosphaadamantane)] is reported. Pd(II) and Pt(II) complexes with the anion of 9-mhypH of the type [M(dmba)(L)(9-mhyp-N1)] [L = PPh₃ or PTA] have also been prepared. The crystal structures of [Pt(dmba)(PPh₃)(9-mhypH-N7)]ClO₄ and [Pt(dmba)(PPh₃)(9-mhyp-N1)] have been established by X-ray diffraction. The last complex is the first structurally authenticated example of N1 coordination of 9-methylhypoxanthine to platinum. DFT-based calculations at the BP86/def2TZVP level predict a most favourable interaction (both kinetically and thermodynamically) of the metal(II) centre with N7 in the neutral ligand 9-mhypH, but with N1 in the deprotonated ligand 9-mhyp⁻ in agreement with the experimentally observed preference in neutral conditions or upon basic treatment, respectively.