Gas phase fragmentation of adducts between dioxygen and closo-borate radical anions

[Display omitted] •Radical anions [closo-B12I11]2−, [1-H-closo-1-CB11I10]− and related derivatives spontaneously add O2 addition in the gas phase.•CID of these O2 adducts shows a previously unprecedented fragmentation behavior for iodinated closo-borates.•We investigated the fragmentation pathways of such O2 adducts by systematically varying the boron bound substituents.•We show that the neutral loss of BO2 can only occur from the CB11 based ions but not from B12 based ions and provide theoretical insights on this dissociation pathway.•Dioxygen can be substituted by other reagents of radical nature which results in very different fragmentation pathways. The icosahedral closo-borate anions, [closo-B12X12]2− (B12) and [1-H-closo-1-CB11X11]− (CB11) with X=H or halogen, are exceptionally stable weakly coordinating anions. Recent studies, which focused on the gas phase ion chemistry of this class of anions, revealed several unusual ion-molecule and unimolecular dissociation pathways. Herein, we demonstrate that collisional activation of highly iodinated closo-borate anions results in a loss of an iodine atom followed by a spontaneous addition of O2 present in a mass spectrometer background producing B12-O2 and CB11-O2 species. We examined the electronic structure of a representative O2 adduct using photoelectron spectroscopy and explored collision-induced dissociation (CID) pathways of a series of iodinated B12-O2 and CB11-O2 anions with different substituents. A systematic study of the gas phase dissociation pathways of the B12-O2 and CB11-O2 anions revealed several unusual dissociation pathways characteristic of this class of species. Abundant fragment ions are formed by neutral loss of BOX2 (X = boron bound substituent), Y2H (Y = boron bound halogen, if any H is present in the molecular ion) and BO2. Loss of BO2 was observed for CB11-O2 but not for B12-O2 anions. Substantial differences in stability of the corresponding fragments are responsible for the observed differences in dissociation of B12-O2 and CB11-O2 species. Furthermore, we show that in addition to O2 other molecules with a radical character (e.g. SCH3) can form adducts with closo-borate anions after iodine abstraction. The boron cage fragmentation observed for the O2 adducts is atypical for highly iodinated closo-borates and is attributed to the strength of BO bonds which dominate the thermochemistry of B12-O2 and CB11-O2 fragmentation reactions.