Formations and electrochemical behavior of mononuclear and binuclear molybdenum dithiolene complexes with nitrosyl ligands: Evidence for the formation of a coordinatively unsaturated species [Cp∗Mo(NO)(dithiolene)]

The one-pot reaction of [Cp∗Mo(NO)(CO)2] with elemental sulfur and dimethyl acetylenedicarboxylate (C2Z2 (Z = COOMe)) gave the [2+2] cycloadduct of the mononuclear molybdenum dithiolene complex [Cp∗Mo(NO)(S2C2Z2)(C2Z2)] (1), and some binuclear complexes:[Cp∗Mo(NO)(S2C2Z2)]2 (2), [Cp∗2Mo2(NO)2S2(S2C2Z2)] (3) and [Cp∗Mo(NO)S2]2 (4).The reaction of [Cp∗Mo(NO)(Cl)(μ-Cl)]2 with Odouble bond; length as m-dashC{S2C2(COOMe)2} in the presence of sodium methoxide also produced complex 2 and the paramagnetic Cp∗Mo bisdithiolene complex [Cp∗Mo(S2C2Z2)2] (5, Z = COOMe).The structures of complexes 1–5 were determined by X-ray crystal structure analysis.The nitrosyl ligands of complexes 1–4 showed a linear coordination to the molybdenum center (the Mo–N–O bond angles = 169–174°), and their N–O bond lengths were 1.17–1.20 Å.In the binuclear complexes 2–4, two nitrosyl ligands were placed at cis-position.Complexes 1 and 2 were characterized by cyclic voltammetry and spectroelectrochemistry (visible and IR). The electrochemical reduction of the dimeric complex 2 formed the monomeric dithiolene complex[Cp∗Mo(NO)(S2C2Z2)]− (X−) whose lifetime was several minutes. When the anion X− was electrochemically oxidized, the coordinatively unsaturated species X was generated, but it was immediately dimerized to afford the original dimeric complex 2. The reduction of the complex 1 included the elimination of the bridged DMAD moiety (C2Z2) to give the anion X−.