Fluoroolefin condensation catalyzed by aluminum chlorofluoride

High-fluorine-content aluminum chlorofluoride, as prepared by Cl/F exchange of aluminum chloride with one of a number of organofluorine compounds, is a very active Lewis acid capable of condensing an allylic fluoride with another fluoroolefin at low temperature. In addition to a description of broader scope, details of the selective reaction of hexafluoropropene with tetrafluoroethylene to form F-pentene-2 are presented along with evidence supporting polyfluoroallyl cationic species as intermediates. Ab initio calculations confirm the feasibility of the proposed mechanism and further suggest that 1,3-fluorine shifts in fluorocarbocations are energetically accessible at modest temperatures. Revised heats of formation for C3F8 (Delta H-f(0) = -1750 +/- 12.4 kJ mol(-1)) and HFP (Delta H-f(0) = -1128 +/- 5 W mol(-1)) have been calculated. Fluoride affinities of some simple metallohalogens are reported.