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

Treatment
of the aromatic nitrile complexes trans-[PtCl2(RC6H4CN)2] (R = p-CF3 NC1, H NC2, o-Cl NC3) with the aryl amidoximes p-R′C6H4C­(NH2)NOH
(R′ = Me AO1, H AO2, Br AO3, CF3 AO4, NO2 AO5) in all combinations, followed by addition of 1 equiv of AgOTf and
then 5 equiv of Et3N, leads to the chelates [PtCl­{HNC­(RC6H4)­ONC­(C6H4R′-p)­NC­(RC6H4)NH}] (1–15; 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 1–16 were characterized
by elemental analyses (C, H, N), high-resolution ESI+-MS,
FTIR, and 1H NMR techniques, whereas unstable 17 was characterized by HRESI+-MS and FTIR. In addition, 8·C4H8O2, 12, and 16·CHCl3 were studied by single-crystal
X-ray diffraction.