Sequential Reduction of Borylstibane to an Electronically Nonsymmetric Diboryldistibene Radical Anion.

Understanding the formation of metal-metal bonds and their electronic structures is still a scientific task. We herein report on the stepwise synthesis of boryl-substituted antimony compounds in which the antimony atoms adopt four different oxidation states (+III, +II, +I, +I/0). Sb-C bond homolysis of Cp*[(HCNDip)B]SbCl (; Cp* = CMe; Dip = 2,6-PrCH) gave diboryldichlorodistibane [(HCNDip)BSbCl] (), which reacted with KC to form diboryldistibene [(HCNDip)BSb] () and traces of cyclotetrastibane [(HCNDip)B]SbCl (). One-electron reduction of yielded the potassium salt of the diboryldistibene radical anion [(HCNDip)BSb]̇, [K(18--6)(OEt)][{(HCNDip)BSb}] (), which exhibits an unprecedented inequivalent spin localization on the Sb-Sb bond and hence an unsymmetric electronic structure. Compounds were characterized by heteronuclear nuclear magnetic resonance (NMR) (H, C, B), infrared (IR), ultraviolet-visible (UV-vis) spectroscopy (, ), and single crystal X-ray diffraction (sc-XRD, ), while the bonding nature of and was analyzed by quantum chemical calculations. EPR spectroscopy resolves the dissimilar Sb hyperfine tensors of , reflecting the inequivalent spin distribution, setting uniquely apart from all previously characterized dipnictene radical anions.