From a Paramagnetic, Mononuclear Supersulfidonickel(Ⅱ) Complex to a Diamagnetic Dimer with a Four-Sulfur Two-Electron Bond

摘要

Transition-metal complexes of diatomic chalcogen ligands X_2 are of interest because of their role in oxidation processes in biological and catalytic systems. Owing to their importance, respective peroxo (O_2~(2-)) as well as persulfido (disulfido) complexes (S_2~(2-)) have attracted much attention, resulting in a vast number of complexes for structure-reactivity studies containing one or more X_2 units with a "side-on" or "end-on" coordination mode. In contrast, much less is known about complexes containing the paramagnetic superoxo (O_2~- ) and supersulfido (S_2~-) ligand, respectively, despite the fact that they can be key intermediates in metal-mediated X-X bond activation and X-atom transfer reactions. Thus it is challenging in synthetic chemistry to develop isolable superchalcogenidometal complexes capable of soft X-atom transfer for chemoselective C-H bond functionalization. Up to now, the elusive S_2~- radical anion could only be detected by spectroscopy and only a few "end-on" supersulfido complexes have been characterized structurally. A "side-on" supersulfido complex is as yet unknown. Recently, we developed a simple route to the first isolable superoxonickel complex [LNi(O_2)] bearing a tetracoordinate Ni(Ⅱ) center by taking advantage of the electronic nature of the bulky substituted, monoanionic β-diketiminate ligand L~-, CH{(CMe)(2,6-~1Pr_2C_6H_3N)}_2~(-6). The latter complex results from one-electron reduction of O_2 by the corresponding Ni(I) precursor. Its fascinating magnetic properties and reactivity prompted us to probe whether the supersulfidonickel homologue 1 could be synthesized by direct oxidation of the same Ni(Ⅰ) precursor, [(LNi)_2(toluene)] 2, with elemental sulfur. Herein, we report the facile synthesis, the striking structural features, and the reactivity of the first supersulfidonickel complex 1 with the "side-on" S_2~- ligand.