The reaction of CF4 with Cp2Ln–H has been studied with DFT(B3PW91) calculations for the entire family of lanthanide elements. The reaction paths for H/F exchange (formation of CF3H and Cp2Ln–F) and alkylation (formation of Cp2Ln–CF3 and HF) have been determined. Even though a transition state for formation of Cp2Ln–CF3 has been located, Cp2Ln–CF3 reacts with no energy barrier with HF to give Cp2Ln–F and CF3H. The products of the reactions of H/F exchange and alkylation are thus identical. The former reaction is found to be kinetically preferred although the energy barrier is high (>30 kcal mol−1) which suggests that CF4 would not react with Cp2Ln–H derivatives. These reactions contrast with that of CH4 and Cp2Ln–H for which the energy barrier for the alkylation reaction is lower. The difference in the energy barriers is attributed to an unfavourable charge distribution in the 3c–4e transition state. The structure of Cp2Ln–CF3 differs from that of Cp2Ln–CH3. Because of the high affinity of Ln for F, CF3 is dihapto-η2-C–F bonded. The LnF interaction is strong and Cp2Ln–CF3 can be viewed as an F bridged Ln–CF2 complex. The presence of a nascent carbene CF2 group in this complex rationalizes its reactivity with HF.