Isolated [B2(CN)6]2-: Small Yet Exceptionally Stable Nonmetal Dianion

Reactivity of a Hexaaryldiboron(6) Dianion as Boryl Radical Anions

Our study unveils a novel approach to accessing boryl radicals through the spontaneous homolytic cleavage of B-B bonds. We synthesized a hexaaryl-substituted diboron(6) dianion, 1, via the reductive B-B coupling of 9-borafluorene. Intriguingly, compound 1 exhibits the ability to undergo homolytic B-B bond cleavage, leading to the formation of boryl radical anions, as confirmed by EPR studies, in the presence of the 2.2.2-cryptand at room temperature. Moreover, it directly reacts with diphenylacetylene, producing an unprecedented 1,6-diborylated allene species, where the phenyl ring is dearomatized. Density functional theory computational studies suggest that homolytic B-B bond cleavage is favored in the reaction path, and the formation of the boryl radical anion is crucial for dearomatization. Additionally, it achieves the dearomative diborylation of anthracene and the activation of elemental sulfur/selenium under mild conditions. The borylation products have been successfully characterized by NMR spectra, HRMS, and X-ray single-crystal diffraction.

Lewis Acid Decorated Hexacyanodiborane(6) Dianion

First examples of diborane(6) dianions decorated with weakly coordination B(C6F5)3 (BCF) groups and SiEt3 + moieties have been synthesized demonstrating the synthetic potential of the [B2(CN)6]2- dianion. [B2{CNB(C6F5)3}6]2- (1) was isolated as potassium and tetrabutylammonium salt. 1 is a rare example for a weakly coordinating dianion and it was used for the stabilization of the carbocation [Ph3C]+ and the oxonium acid [H(OEt2)2]+. Reaction of [Ph3C]21 with HSiEt3 resulted in the silylated neutral diborane(6) [B2{CNB(C6F5)3}4(CNSiEt3)2] (2) in which two BCF groups have been selectively replaced by SiEt3 + substituents, underscoring the stability and chemical versatility of the [B2(CN)6]2- dianion. The chemical properties and physicochemical data of 1 and 2 provide insight into electronic, coordinating, and steric properties of theses novel diborane(6) compounds.

Dismutation of Tricyanoboryllead Compounds: The Homoleptic Tetrakis(tricyanoboryl)plumbate Tetraanion

A series of unprecedently air‐stable (tricyanoboryl)plumbate anions was obtained by the reaction of the boron‐centered nucleophile B(CN)₃²⁻ with triorganyllead halides. Salts of the anions [R₃PbB(CN)₃]⁻ (R=Ph, Et) were isolated and found to be stable in air at room temperature. In the case of Me₃PbHal (Hal=Cl, Br), a mixture of the anions [Me_4−nPb{B(CN)₃}_n]ⁿ⁻ (n=1, 2) was obtained. The [Et₃PbB(CN)₃]⁻ ion undergoes stepwise dismutation in aqueous solution to yield the plumbate anions [Et_4−nPb{B(CN)₃}_n]ⁿ⁻ (n=1–4) and PbEt₄ as by‐product. The reaction rate increases with decreasing pH value of the aqueous solution or by bubbling O₂ through the reaction mixture. Adjustment of the conditions allowed the selective formation and isolation of salts of all anions of the series [Et_4−nPb{B(CN)₃}_n]ⁿ⁻ (n=2–4) including the homoleptic tetraanion [Pb{B(CN)₃}₄]⁴⁻.