Amidrazone Complexes from a Cascade Platinum(II)-Mediated Reaction between Amidoximes and Dialkylcyanamides

The aryl amidoximes R′C₆H₄C­(NH₂)NOH (R′ = Me, <b>2a</b>; H, <b>2b</b>; CN, <b>2c</b>; NO₂, <b>2d</b>) react with the dialkylcyanamide platinum­(II) complexes <i>trans</i>-[PtCl₂(NCNAlk₂)₂] (Alk₂ = Me₂, <b>1a</b>; C₅H₁₀, <b>1b</b>) in a 1:1 molar ratio in CHCl₃ to form chelated <i>mono</i>-addition products [<b>3a</b>–<b>h</b>]­Cl, viz. [PtCl­(NCNAlk₂)­{<u>N</u>HC­(NR₂)­O<u>N</u>C­(C₆H₄R′)­NH₂}]Cl (Alk₂ = Me₂; R′ = Me, <b>a</b>; H, <b>b</b>; CN, <b>c</b>; NO₂, <b>d</b>; Alk₂ = C₅H₁₀; R′ = Me, <b>e</b>; H, <b>f</b>; CN, <b>g</b>; NO₂, <b>h</b>). In the solution, these species spontaneously transform to the amidrazone complexes [PtCl₂{<u>N</u>HC­(NR₂)­NC­(C₆H₄R′)<u>N</u>NH₂}] (<b>7a</b>–<b>h</b>; 36–47%); this conversion proceeds more selectively (49–60% after column chromatography) in the presence of the base (PhCH₂)₃N. The observed reactivity pattern is specific for NCNAlk₂ ligands, and it is not realized for conventional alkyl- and arylnitrile ligands. The mechanism of the cascade reaction was studied by trapping the isocyanate intermediates [PtCl­(NCO)­{<u>N</u>HC­(NR₂)­NC­(C₆H₄R′)<u>N</u>NH₂}] (<b>5a</b>–<b>h</b>) and also by ESI-MS identification of the ammonia complexes [PtCl­(NH₃)­{<u>N</u>HC­(NR₂)­NC­(C₆H₄R′)<u>N</u>NH₂}]⁺ ([<b>6a</b>–<b>h</b>]⁺) in solution. The complexes [<b>3a</b>]Cl, [<b>3c</b>–<b>h</b>]Cl, <b>5a</b>–<b>h</b> and <b>7a</b>–<b>h</b> were characterized by elemental analyses, high resolution ESI-MS, IR, and ¹H NMR techniques, while <b>5b</b>, <b>5d</b>, <b>5g</b>, <b>7b</b>, and <b>7e</b> were also studied using single-crystal X-ray diffraction