The free energy of TS1 -with respect to I -is somewhat similar for each of the substrates bearing an N-heterocyclic directing group (-4.0 to -8.2 kcal/mol) and is slightly higher for the other substrates (-1.4 to 2.0 kcal/mol). In all cases, the C-H activation step is endergonic overall, by 2.2 to 10.6 kcal/mol. While not modelled here, the next steps would be exchange of the hydride ligand with a hydrogen from the dihydrogen (or D2) ligand (typically termed 'hydrogen fluxionality') and C-D bond formation. Barriers for C-H activation are broadly comparable for oxygen-based (19.6 to 26.9 kcal/mol) and heterocyclic directing groups (20.1 to 26.8 kcal/mol).