Dynamic processes of H-atom site exchange in trans dihydrogen hydride complex of ruthenium

Abstract

A 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 T₁ 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 -[(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 (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 (ΔG≠) 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.