The TS was located on the singlet PES in line with a two-electron reduction and the need of bimetallic activation since each Lu II is only able to do one single electron transfer. The H 2 molecule is becoming end-on coordinated to the Lu center (Lu-H distance of 2.20 Å) while the H-H distance is only marginally elongated with respect to the adduct (0.88 Å). The second H•••Lu distance remains long (3.47 Å) but the interaction is effective, as highlighted by the HOMO at the TS (Figure ), where the two d z 2 orbitals located on the two Lu atoms overlap with the H 2 σ* orbital. Following the intrinsic reaction coordinate (IRC), it yields two Lu III -H complexes whose formation is highly favorable (-36.4 kcal•mol -1 with respect to the entrance channel).