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Dynamic Processes of H-Atom Site Exchange In Trans Dihydrogen Hydride Complex of Ruthenium

National Institute for Science Comminication
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  • Inorganic & Physical Chemistry


A new dihydrogen hydride complex of ruthenium of the type trans-$[(dppm)Ru(H)(h^2-H_2)(PPh_3)_2][BF_4] (l) (dppm = Ph_2PCH_2PPh_2)$ has been prepared by protonating the precursor dihydride complex cis-$[(dppm)Ru(H)_2(PPh_3)_2]$ using $HBF_4.Et2O$. The formulation of (l) as a dihydrogen complex has been based upon the variable temperature $T_1$ measurements $(T_1(min) = 12.4 ms at 273 K, ClCD_2CD_2Cl, 400 MHz)$ and the observation of a substantial H-D coupling constant $(J(H,D) = 32 Hz, 243 K, ClCD_2CD_2Cl)$ for the corresponding HD isotopomer trans-$[(dppm)Ru(H)(h^2-HD)(PPh_3)_2][BF_4]$. 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 (l) show dynamic behavior and undergo rapid H-atom site exchange at 343 K. At 273 K (l) shows a static structure. The dynamics of (l) involving a trihydride intermediate has been studied by variable temperature NMR spectroscopy. The barrier to site exchange of the H-atom between the dihydrogen with the hydride (DG‡) has been determined to be 14.4 kcal/mol at 303 K. Compound (l) has been found to be stable up to 343 K in solution and no loss of the $H_2$ ligand has been observed at that temperature; in addition, the compound is stable in solution at room temperature for a period of two days.

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