The catalytic C-H metalation reactions were modelled with 2-methyl-thiophene, 2a, as a prototypical substrate using the full NacNac ligand. Geometry optimizations employed the BP86 functional and a modest basis set (Zn: SDD; Al/S: SDD with polarization; other atoms: 6-31G**). Electronic energies were then corrected for the effects of solvation (PhCl, PCM) and dispersion (DFT-D3(BJ)) and recomputed with the def2-TZVP basis set using the B3PW91 functional. The thermochemical corrections from the BP86 frequency calculations were then added to give the free energies quoted in the text. This protocol was selected after extensive functional testing and conformational searching of key stationary points involving a bound NEt3 ligand (Tables and).