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) 2 B]SbCl ( 1 ; Cp* = C 5 Me 5 ; Dip = 2,6- i Pr 2 C 6 H 3 ) gave diboryldichlorodistibane [(HCNDip) 2 BSbCl] 2 ( 2 ), which reacted with KC 8 to form diboryldistibene [(HCNDip) 2 BSb] 2 ( 3 ) and traces of cyclotetrastibane [(HCNDip) 2 B] 3 Sb 4 Cl ( 5 ). One-electron reduction of 3 yielded the potassium salt of the diboryldistibene radical anion [(HCNDip) 2 BSb] 2 ̇ - , [K(18- c -6)(OEt 2 )][{(HCNDip) 2 BSb} 2 ] ( 4 ), which exhibits an unprecedented inequivalent spin localization on the Sb-Sb bond and hence an unsymmetric electronic structure. Compounds 1-4 were characterized by heteronuclear nuclear magnetic resonance (NMR) ( 1 H, 13 C, 11 B), infrared (IR), ultraviolet-visible (UV-vis) spectroscopy ( 3 , 4 ), and single crystal X-ray diffraction (sc-XRD, 1-5 ), while the bonding nature of 3 and 4 was analyzed by quantum chemical calculations. EPR spectroscopy resolves the dissimilar Sb hyperfine tensors of 4 , reflecting the inequivalent spin distribution, setting 4 uniquely apart from all previously characterized dipnictene radical anions.