GENERATION AND REACTIVITY OF CHROMIUM FLUORIDE CATIONS (CRFN-4) IN THE GAS-PHASE(, N=0)

Gaseous chromium fluoride monocations CrFn+ (n = 1-4) can be prepared by sequential fluorine-atom transfer from nitrogen trifluoride, NF3, t o chromium cation. In addition, formal F- anion transfer to CrFn+ (n = 2-4) to yield the corresponding neutral chromium fluorides CrFn+1 is observed. In conjunction with a re-evaluation of previous data, the pr esent results provide a consistent picture of the thermochemistry of n eutral and cationic chromium fluorides. The reactivity of the CrFn+ io ns towards alkanes is investigated in a Fourier-transform ion cyclotro n resonance mass spectrometer. While ''bare'' Cr+ does not react with alkanes, the chromium fluoride cations CrFn+ do; CrF3+ and CrF4+ are e ven capable of activating methane. With both increasing oxidation stat e of chromium and increasing chain lengths of the alkane, the branchin g ratio of the possible reaction pathways shifts from homolytic C-H an d C-C bond activation to hydride- and methanide-ion transfer to yield carbocations, and finally electron transfer generating hydrocarbon rad ical cations.