Dynamic processes of H-atom site exchange in <i>trans </i>dihydrogen hydride complex of ruthenium

27-33A new dihydrogcn hydride complex of ruthenium of the type trans-[(dppm )Ru (H)(η2-H2)(PPh3)2][BF4] (1) (dppm =Ph2PCH2PPh2) has been prepared by protonating the precursor dihydride complex cis- -[(dppm )Ru (H)2( (PPh3)2] using HBF4.Et2O. The fmmulation of (1) as a dihydrogen complex has been based upon the variable temperature T<span style="mso-bidi-font-style: italic">1 measurements (T1 (min) = 12.4 ms at 273 K, ClCD2CD2Cl, 400 MHz) and the observation of a substantial H-D coupling constant (J(H,D) = 32 Hz, 243 K, ClCD2CD2Cl) for the corresponding HD isotopomer trans <i style="mso-bidi-font-style: normal">-[(dppm )Ru (H)(η2-HD) (PPh3)2][BF4]. The T1 and the H-D coupling constant measurements have been carried out in the temperature range 243- 283 K. The dihydrogen and the hydride ligands of (<b style="mso-bidi-font-weight: normal">1) show dynamic behavior and undergo rapid H-atom site exchange at 343 K. At 273 K (1) shows a static structure. The dynamics of (1) involving a trihydride intermediate has been studied by variable temperature NMR spectroscopy. The barrier to site exchange of the H-atom bet ween the dihydrogen with the hydride (∆Gǂ) has been determined to be 14.4 kcal/mol at 303 K. Compound (1) has been found to be stable up to 343 K in solution and no loss of the H2 ligand has been observed at that temperature; in addition, the compound is stable in solution at room temperature for a period of two days