Sequential Reduction of Borylstibane to an ElectronicallyNonsymmetric Diboryldistibene Radical Anion

Understanding the formation of metal-metal bondsand their electronic structures is still a scientific task. We hereinreport on the stepwise synthesis of boryl-substituted antimonycompounds in which the antimony atoms adopt four differentoxidation states (+III, +II, +I, +I/0). Sb-C bond homolysis ofCp*[(HCNDip)2B]SbCl (1;Cp*=C5Me5; Dip = 2,6-iPr2C6H3)gave diboryldichlorodistibane [(HCNDip)2BSbCl]2(2), whichreacted with KC8to form diboryldistibene [(HCNDip)2BSb]2(3)and traces of cyclotetrastibane [(HCNDip)2B]3Sb4Cl (5). One-electron reduction of3yielded the potassium salt of thediboryldistibene radical anion [(HCNDip)2BSb]2?-, [K(18-c-6)-(OEt2)][{(HCNDip)2BSb}2](4), which exhibits an unprece-dented inequivalent spin localization on the Sb-Sb bond and hence an unsymmetric electronic structure. Compounds1-4werecharacterized by heteronuclear nuclear magnetic resonance (NMR) (1H,13C,11B), infrared (IR), ultraviolet-visible (UV-vis)spectroscopy (3,4), and single crystal X-ray diffraction (sc-XRD,1-5), while the bonding nature of3and4was analyzed byquantum chemical calculations. EPR spectroscopy resolves the dissimilar Sb hyperfine tensors of4,reflecting the inequivalent spindistribution, setting4uniquely apart from all previously characterized dipnictene radical anions.

Automated summary

In this study, the stepwise synthesis of boryl-substituted antimony compounds was reported, revealing the formation of metal-metal bonds and the changes in electronic structures. The molecular structures and bonding properties were characterized and analyzed in detail through experimental and computational methods. The results showed that the synthesized compounds exhibited unique spin distribution and asymmetric electronic structures.