Sequential Reduction of Borylstibane to an Electronically Nonsymmetric Diboryldistibene Radical Anion

Abstract

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-iPr 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). Oneelectron 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.

Synthesis, Reactivity, and Theoretical Insights of Co-Sb2 and Co-Bi2 Rings

“…1 H and 31 P{ 1 H} NMR as well as 13 C{ 1 H} NMR spectra were recorded in C 6 D 6 or THF-d 8 at 25 °C using a Bruker Avance I 300 MHz, Bruker Avance I 400 MHz, Bruker Avance III HD Ascend 500 MHz, and Bruker Avance III HD Ascend 700 MHz. 1 H NMR was reported as follows: chemical shift, multiplicity (s = singlet, d = doublet and t = triplet), coupling constant (J values) in Hz and integration.…”

“…Chemical shifts (δ) were reported with respect to the corresponding solvent residual peak at 7.16 ppm for C 6 D 6 and 1.73 ppm for THF-d 8 . 13 C NMR spectra ( 1 H-broadband decoupled) were reported in ppm using the central peak of C 6 D 6 (128.08 ppm) and of THF-d 8 (25.37 ppm).…”

From Neutral Diarsenes to Diarsene Radical Ions and Diarsene Dications

“…Diarsene ( V ), and dibismuthene ( II ) radical anions have only been recently structurally characterized, whereas the first distibene radical anion ( IV) was reported in 2006 (Scheme 1). [14,15] Dipnictenes radical anions possess a highly reductive nature and their reactivity is still hardly explored [11d,13,16] . In addition, radical cations of heavy dipnictenes are limited to diarsenes, which have been synthesized by single electron oxidation of NHC‐ ( VII ) and NHO‐coordinated ( VI ) diarsenes (Scheme 1).…”

Light‐Dependent Reactivity of Heavy Pnictogen Double Bonds

“…[18][19][20][21] Noteworthy, the ones reported were accessed via in situ trapping of the dipnictenes, showcasing the difficulty in activating such a bond and thus the restrained applicability to a specific class of transition metals (Figure 1, B). This motivated the seek for alternative ligand platforms such as NHC (N-heterocyclic carbene), [22] boryl, [23] and gallyl as a tool to tune the reactivity. [24] Specifically, examples of electron transfer, [25,26] cycloaddition [27] and small molecule activation reactions were reported.…”