Bioinspired Persulfidation of a Mononuclear Ni(II)-ONO Compound: Evidence for Sulfur/Nitrogen “Crosstalk”

Reactivity of a mononuclear Ni(II)-ONO compound, [Ni(6-COO–-tpa)(ONO)] (2), with MeC(O)SH in a 1:2 ratio generated an unprecedented Ni(II)-persulfide compound, [Ni(6-COO–-tpa)(SSC(O)Me)] (5), along with nitric oxide (NO) and nitrous oxide (N2O). The reaction proceeds by the generation of nitrous acid (HONO) and [Ni(6-COO–-tpa)(SC(O)Me)] (4) followed by the reaction of free ONO– (from HONO) with either the coordinated MeC(O)S– in 4 or free MeC(O)S– to release thionitrite (SNO–) and MeC(O)O–. In the presence of protons, SNO– is converted to perthionitrite (SSNO–) and N2O (minor pathway). SSNO– decomposes to liberate elemental sulfur ([S]), which then reacts with the coordinated MeC(O)S– in 4 to generate 5. In contrast to this, SSNO–, generated in the reaction of 2 and MeC(O)S– in a 1:2 ratio, decomposes in the absence of protons to produce Sn2–, which, in turn, produces a rare example of a Ni(II)-SH compound, [Ni(6-COO–-tpa)(SH)] (6). All the Ni(II) compounds and the intermediates have been characterized by a combination of structural and spectroscopic studies, and, based on these results, mechanisms for the reactions have been proposed. The present work thus demonstrates perthionitrite-mediated persulfidation involving mononuclear Ni(II) complexes 2 and 4, to generate the only example of a Ni(II)-persulfide compound, 5.