Electrophilic anions of type [B 12 X 11 ] À posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B 12 X 11 ] À with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N 2 as σ-donor-π-acceptors. Temperature-dependent formation of [B 12 X 11 NG] À indicates the enthalpy order (X=CN) > (X=Cl) � (X=Br) > (X=I) � (X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B 12 X 11 ] À and steric effects. The binding of CO and N 2 to [B 12 X 11 ] À is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F) > (X=CN) > (X=Cl) > (X=Br) > (X=I), in contrast to the NG series. The bonding motifs of [B 12 X 11 CO] À and [B 12 X 11 N 2 ] À were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N 2 stretching frequencies n CO and n N 2 , respectively. Observed shifts of n CO and n N 2 are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B 12 X 11 ] À reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions.

We report on cluster‐mediated C−N bond formation in the gas phase using N2 as a nitrogen source. The V3C++N2 reaction is studied by a combination of ion‐trap mass spectrometry with infrared photodissociation (IRPD) spectroscopy and complemented by electronic structure calculations. The proposed reaction mechanism is spectroscopically validated by identifying the structures of the reactant and product ions. V3C+ exhibits a pyramidal structure of C1‐symmetry. N2 activation is initiated by adsorption in an end‐on fashion at a vanadium site, followed by spontaneous cleavage of the N≡N triple bond and subsequent C−N coupling. The IRPD spectrum of the metal nitride product [NV3(C=N)]+ exhibits characteristic C=N double bond (1530 cm−1) and V−N single bond (770, 541 and 522 cm−1) stretching bands.

The vibrational frequency of CO, which binds to different electrophilic anions [B12X11]‐ (X=F, Cl, Br, I), is determined by an interplay of blue‐shifting electrostatics (blue beam between boron and carbon) and red shifting π‐backdonation (flames). For X=Cl, Br, I, (upper half) electrostatics dominates, while for X=F (bottom) π‐backdonation dominates and binds CO exceptionally strongly. Measured spectra are shown on the right. The band of unbound CO would be found at the position of the laser beam. More information can be found in the Full Paper by M. Mayer, J. Warneke, et al. (DOI: 10.1002/chem.202100949).