Photo-Induced Hydrogenation of a Cationic Triruthenium Complex Capped by a μ ₃ -η ³ -C ₃ Ring: Fluxional Behavior of Hydrides in a Cationic Triruthenium Diruthenaallyl Complex with an Agostic Ru–H–C Interaction

Under photoirradiating conditions, a cationic triruthenium complex containing a μ3-η3-C3 ring, [(Cp*Ru)3(μ3-CH)(μ3-η3-C3MeH2)]+ (1, Cp* = η5-C5Me5), reacts with dihydrogen at 25 °C to yield a mixture of cationic μ3-η3-diruthenaallyl complexes, [(Cp*Ru)3(μ3-CH)(μ3-η3:η2-HCHCMeCH)(μ-H)]+ (4a) and [(Cp*Ru)3(μ3-CH)(μ3-η3:η2-HCMeCHCH)(μ-H)]+ (4b), together with a paramagnetic μ3-diruthenaallyl complex, [(Cp*Ru)3(μ3-CH)(μ3-η3-CHCMeCH)(μ-H)]+ (6), via the elimination of a hydrogen radical from 4a and 4b. X-ray diffraction studies revealed that 4a contains an agostic Ru–H–C interaction between the Ru, H, and the α carbon atom of the allylic moiety. Two hydrides in 4a undergo rapid site-exchange, generating a time-averaged CS spectrum even at −80 °C. DFT calculations suggest that intermediate 5, containing a μ-η2-H2 ligand, is involved in the dynamic process, and the free energy of activation of the process is estimated to be 6.0 kcal mol–1. Thermolysis of 4a at 150 °C resulted in the clean regeneration of 1 via the elimination of dihydrogen, accompanied by the reconstruction of the μ3-η3-C3 ring. The mutual conversion between 1 and 4a/4b would provide a unique hydrogen storage system that absorbs hydrogen under photoirradiation conditions and releases it upon thermolysis.