The iridium(perfluoropropyl)(vinyl) complex Cp'Ir(PMe3)(n-C3F7)(CH=CH2) (5) has been prepared. It has been characterized by X-ray crystallography, and its ground state conformation in solution has been determined by F-19{H-1} HOESY NMR studies. It reacts with the weak acid lutidinium iodide to afford the eta(1)-allylic complex Cp*Ir(PMe3)((Z)-CH2CH=CFC2F5)I (6), which has also been characterized crystallographically. The mechanism of C-F bond activation and C-C bond formation leading to 6 has been elucidated in detail by studying the reaction of 5 with lutidinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate [LutH(+)B(ArF)(4)(-)], containing a weakly coordinating counteranion. The main kinetic product of this reaction, determined by F-19{H-1} HOESY studies at -50 degrees C, is the endo-Cp*Ir(PMe3)(anti-eta(3)-CH2CHCFCF2CF3)[B(ArF)(4)] diastereomer 9, along with a small amount of the exo-syn-isomer 8. Isomer 9 rearranges at -20 degrees C to its exo-anti isomer 7, and subsequently to the thermodynamically favored exo-syn-isomer 8, which has been isolated and crystallographically characterized. Complex 8 reacts with iodide to afford complex 6. On the basis of the unambiguously defined kinetically controlled stereochemistry of 9 and 8, a detailed mechanism for the C-F activation/C-C coupling reaction is proposed, the principal conclusion of which is that C-F activation is completely diastereoselective.