The structure of TS1 is particularly interesting in view of the cooperative role of the olefin ligand (Figure ). In TS1, H2 undergoes a formal heterolytic cleavage where the olefin is reduced by accepting a hydride equivalent and the nickel center accepts a proton, increasing its oxidation state by two units. The carbon atoms belonging to the olefin (C10 and C41) maintain close to sp 2 character with a bond length of 1.450 Å and sum angles of 348.0º and 352.8º respectively. The fragment is still coordinated in h 2 fashion to the nickel center with similar bond length values than in complex 2. The H-H bond is broken with a distance of 1.536 Å and, both the Ni-H95 (1.456 Å) and Ni-H96 (1.480 Å) distances have become shorter than in structure 2. These structural observations collectively suggest that the transition state has a strong dihydride character, the metal being already oxidized to Ni(II).