Facile cyanamide–ammonia coupling mediated by cis- and trans-[Pt^IIL₂] centers and giving metal-bound guanidines

Diffusion of ammonia into CH₂Cl₂ solutions of the dialkylcyanamide complexes cis- or trans-[PtCl₂(RCN)₂] (R = NMe₂, NEt₂, NC₅H₁₀) at 20–25 °C leads to metal-mediated cyanamide–ammonia coupling to furnish, depending on reaction time, one or another type of novel bisguanidine compound, i.e. the molecular cis- or trans-[PtCl₂{NHC(NH₂)R}₂] (cis-1–3 and trans-1–3) and the cationic cis- or trans-[Pt(NH₃)₂{NHC(NH₂)R}₂](Cl)₂ (cis-4–6 and trans-4–6) complexes. Compounds cis-1–3 or trans-1–3 were converted to cis-4–6 or trans-4–6, accordingly, upon prolonged treatment with NH₃ in CH₂Cl₂. The ammination of the relevant nitrile complexes cis- or trans-[PtCl₂(RCN)₂] (R = Et, CH₂Ph, Ph) in CH₂Cl₂ solutions affords only the cationic compounds cis- or trans-[Pt(NH₃)₂{NHC(NH₂)R}₂](Cl)₂ (cis-7–9 and trans-7–9). The formulation of 1–9 was supported by satisfactory C, H and N elemental analyses, agreeable ESI⁺-MS (or FAB⁺-MS), IR, ¹H and ¹³C NMR spectroscopies. The structures of trans-1, trans-3, cis-4, trans-4, cis-7, and cis-9 were determined by single-crystal X-ray diffraction disclosing structural features and showing that the ammination gives ligated guanidines and amidines in the E- and Z-forms, respectively, where both correspond to the trans-addition of NH₃ to the nitrile species.