Reductive Metalation of Cyclic and Acyclic Pseudopeptidic Bis-Disulfides and Back Conversion of the Resulting Diamidato/Dithiolato Complexes to Bis-Disulfides

Cyclic and acyclic pseudopeptidic bis-disulfides built on an o-phenylene diamine scaffold were prepared: (N2H2S2)2, 1a, N2H2(S-SCH3)2, 1b, and N2H2(S−StBu)2, 1c. Reductive metalation of these disulfides with (PF6)[Cu(CH3CN)4] in the presence of Et4NOH as a base, or with (Et4N)[Fe(SEt)4] and Et4NCl, yields the corresponding diamidato/dithiolato copper(III) or iron(III) complex, (Et4N)[Cu(N2S2)], 2, or (Et4N)2[Fe(N2S2)Cl], 5. These complexes display characteristics similar to those previously described in the literature. The mechanism of the metalation with copper has been investigated by X-band electron paramagnetic resonance (EPR) spectroscopy at 10 K. After metalation of the bis-disulfide 1c and deprotonation of the amide nitrogens, the reductive cleavage of the S−S bonds occurs by two one-electron transfers leading to the intermediate formation of a copper(II) complex and a thyil radical. Complexes 2 and 5 can be converted back to the cyclic bis-disulfide 1a with iodine in an 80% yield. Reaction of 5 wi...