Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Gaseous chromium fluoride monocations CrF_n⁺ (n = 1-4) can be prepared by sequential fluorine-atom transfer from nitrogen trifluoride, NF₃, to chromium cation. In addition, formal F^- anion transfer to CrF_n⁺ (n = 2-4) to yield the corresponding neutral chromium fluorides CrF_n+1 is observed. In conjunction with a re-evaluation of previous data, the present results provide a consistent picture of the thermochemistry of neutral and cationic chromium fluorides. The reactivity of the CrF_n⁺ ions towards alkanes is investigated in a Fourier-transform ion cyclotron resonance mass spectrometer. While "bare" Cr⁺ does not react with alkanes, the chromium fluoride cations CrF_n⁺ do; CrF₃⁺ and CrF₄⁺ are even capable of activating methane. With both increasing oxidation state of chromium and increasing chain lengths of the alkane, the branching ratio of the possible reaction pathways shifts from homolytic C-H and C-C bond activation to hydride- and methanide-ion transfer to yield carbocations, and finally electron transfer generating hydrocarbon radical cations.

Keywords: Chromium fluorides; Gas-phase ion chemistry; C-H bond activation; Electron transfer; Oxidation state.