X-ray Photoelectron Spectroscopy (XPS) measurements show the expected transitions characteristic of -CF2-functional groups from the F(1S) orbitals (689.8 eV) and C(1S) orbitals (292.0 and 284.4 eV) of PTFE (Figure ). The same transitions are also observed in PTFE-R, however integration of peaks in the C(1s) scan show that the C-F : C-C ratio has changed from 1 : 0.5 to 1 : 1.4 consistent with lower fluorine content near the surface of PTFE-R compared to PTFE. In addition, a new transition is observed at 684.7 eV assigned to a Mg bound F(1S) environment (Supplementary Information, Figure ). Hence, while it is clear from the high recovery of 2 that most of the exercised fluorine content is transferred to the solution phase, we cannot discount the retention of small amounts of metal fluoride species at the surface of PTFE-R. Attenuated total reflectance IR spectroscopy also shows clear differences between PTFE and PTFE-R. PTFE-R shows vibrations 1620, 1550, 1006, 985, 852 and 801 cm -1 not present in PTFE, which most likely derive from C=C stretching and bending modes of newly created alkene functional groups (Figure ). To support this assignment, a sample of PTFE-R was reacted with an excess of BH3•THF in THF for 72 h. Following re-isolation of the polymer, the key vibrations assigned to C=C modes are no longer present (as would be expected from hydroboration of the C=C functional group) (Supplementary Information, Figure ). The XPS and IR data suggest that defluorination occurs at the surface of PTFE, most likely with the creation of alkene functionality through a 1,2-defluorination of polymer chains. Octafluorotoluene is proposed to react further with 1 to effect metalation at the 4-position of the newly unsaturated ring system, allowing trapping of the organic fragment to form 3 (Figure ). A control reaction between octafluorotoluene, 1 and DMAP also formed 3. Consideration of the charges on C and F atoms of the breaking C-F bond shows there is charge accumulation on both these sites as the transition state is approached, at the same time positive charge accumulates at the three coordinate Mg atom. The analysis is consistent with a flow of electrons from the main group reagent to C2F6.