(Dien)MII (M = Pd, Pt) and (NH3)3PtII complexes of 1-methylcytosine: Linkage and rotational isomerism, metal-promoted deamination, and pathways to dinuclear species

Despite their structural similarity, [Pt(dien)(1-MeC-N3)]2+ (1), [Pd(dien)(1-MeC-N3)]2+ (2), and [Pt(NH3)3(1-MeC-N3)]2+ (3) (with dien = diethylenetriamine and 1-MeC = neutral 1-methylcytosine) behave in part markedly different at strongly alkaline pH (12–13) and at room temperature. While 1 and 2, yet not 3 show linkage isomerization from N3 to N4, deamination of the cytosine nucleobase to 1-methyluracilate occurs with 1 and 3, yet not with 2. Pathways leading to N3,N4-diplatinated 1-MeC− complexes (1-MeC− = 1-methylcytosine, deprotonated at exocyclic amino group N4) have been studied at high pH by starting from 1 and 3, respectively, and adding (dien)PtII. It appears that initial migration of the metal entity from N3 to N4, followed by binding of the second metal to the available N3 site, is favored over sequential coordination to N3 and then N4. X-ray crystal data of 1–3 density functional theory (DFT) calculations, and NMR (1H, 195Pt) data are presented.