Chemically binding to argon (Ar) at room temperature has remained the privilege of the most reactive electrophiles, all of which are cationic (or even dicationic) in nature. Herein, we report a concept for the rational design of anionic superelectrophiles that are composed of a strong electrophilic center firmly embedded in a negatively charged framework of exceptional stability. To validate our concept, we synthesized the percyano-dodecoborate [B12(CN)12]2−, the electronically most stable dianion ever investigated experimentally. It serves as a precursor for the generation of the monoanion [B12(CN)11]−, which indeed spontaneously binds Ar at 298 K. Our mass spectrometric and spectroscopic studies are accompanied by high-level computational investigations including a bonding analysis of the exceptional B-Ar bond. The detection and characterization of this highly reactive, structurally stable anionic superelectrophile starts another chapter in the metal-free activation of particularly inert compounds and elements.

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B Cl ] spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B Cl Ng] adducts, with Ng binding energies of 80 to 100 kJ mol , contain B-Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B Cl ] anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B Cl CO] and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B Cl ] results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C H ] . This introduces the new chemical concept of "dipole-discriminating electrophilic anions."

Alkanes and [B12X12]2− (X = Cl, Br) are both stable compounds which are difficult to functionalize. Here we demonstrate the formation of a boron−carbon bond between these substances in a two-step process. Fragmentation of [B12X12]2− in the gas phase generates highly reactive [B12X11]− ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. [B12X11]− reacts by an electrophilic substitution of a proton in an alkane resulting in a B−C bond formation. The product is a dianionic [B12X11CnH2n+1]2− species, to which H+ is electrostatically bound. High-flux ion soft landing was performed to codeposit [B12X11]− and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C−H functionalization by [B12X11]− occurred in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for selective bond formation processes and may pave the way for the use of gas-phase ion chemistry for the generation of complex molecular structures in the condensed phase.

While reactions between ions and neutral molecules in the gas phase have been studied extensively, reactions between molecular ions of same polarity remain relatively unexplored. Herein we show that reactions between fragment ions generated in the gas phase and molecular ions of the same polarity are possible by soft‐landing of both reagents on surfaces. The reactive [B 12 I 11 ] 1− anion was deposited on a surface layer built up by landing the generally unreactive [B 12 I 12 ] 2− . Ex‐situ analysis of the generated material shows that [B 24 I 23 ] 3− was formed. A computational study shows that the product is metastable in the gas phase, but a charge‐balanced environment of a grounded surface may stabilize the triply charged product, as suggested by model calculations. This opens new opportunities for the generation of highly charged clusters using unconventional building blocks from the gas phase.