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

Abstract

The reactions of [M(mipk)(H20),I2' (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 'H 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 [Pd,(rnipk),(m~ra)~][ClO~]~ I, [Pd,(mipk),(mthy)2][C104]2 2 and the isotypic compound [Pt,(mipk),(mthy),][C104]2 3 the nucleobases show head-to-tail arrangement. The intramolecular M M distances vary from 2.861(1) 8, in 2 to 2.879(1) A in 1. By ligand-exchange reaction in aqueous media the side product [Pt(mipk),][C104], is formed. Proton NMR studies showed that the dinuclear complexes are not stable in aqueous solution. Oxidation of 3 and [Pt2(mipk),(mura),][C104]2 4 to platinum blues with higher-valent Pt was not observed. Presumably this is due to the competing oxidation of the lowpotential mipk ligand.

Palladium(II) and Platinum(II) Organometallic Complexes with the Model Nucleobase Anions of Thymine, Uracil, and Cytosine: Antitumor Activity and Interactions with DNA of the Platinum Compounds

“…The cyclometalated rings are puckered with the nitrogen atom significantly out of the plane defined by the palladium and carbon atoms, a feature which is quite commonly observed in cyclometalated dmba complexes. The Pd−N(sp 2 ) distances (2.056 and 2.068 Å) are similar to values found for 1-Methy-bridged compounds such as [Pd 2 (mipk) 2 (μ-1-Methy) 2 ] 2+ (2.043 and 2.045 Å) . However the Pd−O (2.150 and 2.133 Å) distances in complex 1 are higher than the corresponding lengths (2.010 and 2.012 Å) in the above-mentioned complex .…”

“…The complex consists of two {( o -C 6 H 4 CH 2 NMe 2 )Pd}fragments each bridged by two 1-methylthyminato ligands through N(3) and O(4) with a head-to-tail arrangement and anti structure. The intramolecular Pd···Pd distance in complex 1 is 3.008(1) Å, a bit longer than the shortest value found so far (2.861 Å) for a head-to-tail 1-methylthyminato-bridged palladium complex which has been observed in [Pd 2 (mipk) 2 (μ-1-Methy) 2 ] 2+ (mipk = 1-methylimidazol-2-yl pyridin-2-yl ketone) . In the related complex [Pd 2 (bpm) 2 (μ-1-Methy) 2 ] 2+ (bpm = bis(pyridine-2-yl)methane), the 1-methylthyminato bridged ligands are arranged in a head-to-head fashion .…”

“…The Pd-N(sp 2 ) distances (2.056 and 2.068 Å) are similar to values found for 1-Methybridged compounds such as [Pd 2 (mipk) 2 (µ-1-Methy) 2 ] 2+ (2.043 and 2.045 Å). 21 However the Pd-O (2.150 and 2.133 Å) distances in complex 1 are higher than the corresponding lengths (2.010 and 2.012 Å) in the above-mentioned complex. 21 A number of cyclometalated dmba complexes with nitrogen and oxygen ligands have been structurally characterized.…”

“…The intramolecular Pd‚‚‚Pd distance in complex 1 is 3.008(1) Å, a bit longer than the shortest value found so far (2.861 Å) for a head-to-tail 1-methylthyminato-bridged palladium complex which has been observed in [Pd 2 (mipk) 2 (µ-1-Methy) 2 ] 2+ (mipk ) 1-methyl-imidazol-2-yl pyridin-2-yl ketone). 21 In the related complex [Pd 2 (bpm) 2 (µ-1-Methy) 2 ] 2+ (bpm ) bis(pyridine-2-yl)methane), the 1-methylthyminato bridged ligands are arranged in a head-to-head fashion. 22 In complex 1 both Pd atoms are slightly out of their coordination planes.…”

Novel Platinum(II) Complexes with Dipyridyl Containing Chelating Ligands and their Products with the Model Nucleobases 1-Methylthymine and 1-Methyluracil

“…Bloemink et al [4] have given a possible explanation for the antitumor activity of compounds lacking an NH moiety: an NH group is probably unnecessary due to the absence of steric hindrance directly around the nitrogen, thus allowing a relatively fast reaction with DNA. As a part of our systematic studies of this type of platinum compounds our interest has been directed to the reactions of complexes with 9-methylguanine, 1-methylcytosine, 1-methylthymine and 1-methyluracil [8,9]. As a part of our systematic studies of this type of platinum compounds our interest has been directed to the reactions of complexes with 9-methylguanine, 1-methylcytosine, 1-methylthymine and 1-methyluracil [8,9].…”