Synthesis, Reactivity, and Electronic Structure of a Bioinspired Heterobimetallic [Ni(μ‑S2)Fe] Complex with Disulfur Monoradical character

The first synthesis of a monoradical Ni­(μ-S2)­Fe core in the [(Nacnac)­Ni­(μ-S2)­Fe­(dmpe)2] complex 3 could be accomplished in good yields by PMe3 elimination from the zerovalent iron complex [(dmpe)2(PMe3)­Fe] (2; dmpe =1,2-bis­(dimethylphosphine)­ethane) upon reaction with the supersulfido nickel­(II) complex [(Nacnac)­Ni­(S2)] (1; Nacnac = CH­{(CMe)­(2,6-iPr2C6H3N)}2). Complex 3 bears Ni­(II) and Fe­(II) centers, both of which are in a low-spin state. A single electron is located in the HOMO and is somewhat delocalized over the Ni­(μ-S2)Fe core, so that the bridging disulfur subunit exhibits some “subsulfide” S23– character. Compound 3 represents a bioinspired example of a monoradical with a Ni­(μ-S2)Fe structural motif, reminiscent of the Ni­(μ-S2)Fe core structure of the active site in [NiFe] hydrogenases. Its oxidation with [Fe­(η5-C5H5)2]­[B­(C6H3(CF3)2)4] affords the product [(Nacnac)­Ni­(μ-S)2Fe­(dmpe)2]­[B­(C6H3(CF3)2)4] (4), and complex 3 can alternatively be prepared via a reductive route upon reaction of [Co­(η5-C5Me5)2]­[(Nacnac)­NiS2] (6) with the Fe(0) precursor 2. All synthesized complexes were fully characterized, including in some cases single-crystal X-ray diffraction analysis, magnetometry, EPR, NMR, and 57Fe Mössbauer spectroscopy. DFT calculations were used to compute the spectroscopic parameters and to establish the electronic structure of 3 and its oxidized and reduced forms and related complexes.