Methane Is the Best Substrate for C(sp³)–H Activation with Cp*(PMe₃)Co(Me)(OTf): A Density Functional Theory Study

The chemical inertness of C­(sp³)–H bonds has made their functionalization difficult, especially with earth-abundant 3d metals. The mechanism of C–H activation with the Co­(III) complex Cp*­(PMe₃)­Co­(CH₃)­(OTf) was studied by DFT at the M06/6-31+G­(d) level of theory and was determined to be in very good agreement with experimental data. The Co­(III) complex can activate the C–H bond of methane through an oxidative hydrogen migration mechanism with an activation free energy of 32.4 kcal/mol in CH₂Cl₂. Although C₂H₆ and <i>c</i>-C₆H₁₂ have weaker C–H bonds than CH₄, their C–H activation barriers were greater at 34.9 and 45.9 kcal/mol, respectively. The C­(sp³)–H and C­(sp²)–H activation of this Co­(III) complex is primarily driven by the sterics (−<i>E</i>′_s) of the substrates and supporting ligands and not the strength of the C–H bond