Bifunctional Reactivity of Amidoximes Observed upon Nucleophilic Addition to Metal-Activated Nitriles

Treatment of the aromatic nitrile complexes <i>trans</i>-[PtCl₂(RC₆H₄CN)₂] (R = <i>p</i>-CF₃ <b>NC1</b>, H <b>NC2</b>, <i>o</i>-Cl <b>NC3</b>) with the aryl amidoximes <i>p</i>-R′C₆H₄C­(NH₂)NOH (R′ = Me <b>AO1</b>, H <b>AO2</b>, Br <b>AO3</b>, CF₃ <b>AO4</b>, NO₂ <b>AO5</b>) in all combinations, followed by addition of 1 equiv of AgOTf and then 5 equiv of Et₃N, leads to the chelates [PtCl­{H<u>N</u>C­(RC₆H₄)­O<u>N</u>C­(C₆H₄R′-<i>p</i>)­NC­(RC₆H₄)<u>N</u>H}] (<b>1</b>–<b>15</b>; 15 examples; yields 71–88% after column chromatography) derived from the platinum­(II)-mediated coupling between metal-activated nitriles and amidoximes. The mechanism of this reaction was studied experimentally by trapping and identification of the reaction intermediates, and it was also investigated theoretically at the DFT level of theory. The combined experimental and theoretical results indicate that the coupling with the nitrile ligands involves both the HON and monodeprotonated NH₂ groups of the amidoximes, whereas in the absence of the base, the NH₂ functionality is inactive toward the coupling. The observed reaction represents the first example of bifunctional nucleophilic behavior of amidoximes. The complexes <b>1</b>–<b>16</b> were characterized by elemental analyses (C, H, N), high-resolution ESI⁺-MS, FTIR, and ¹H NMR techniques, whereas unstable <b>17</b> was characterized by HRESI⁺-MS and FTIR. In addition, <b>8</b>·C₄H₈O₂, <b>12</b>, and <b>16</b>·CHCl₃ were studied by single-crystal X-ray diffraction