Dicationic dihydrogen complexes of osmium and ruthenium

Abstract

The dicationic complexes $\rm\lbrack Os(H\sb2)(PR\sb3)\sb2(bpy)(CO)\rbrack\sp{2+}\ (PR\sb3=PPh\sb3,\ PMePh\sb2),\ \lbrack Os(H\sb2)(PPh\sb3)\sb2(phen)(CO)\rbrack\sp{2+},\ \lbrack Ru(H\sb2)(PPh\sb3)\sb2(bpy)(CO)\rbrack\sp{2+},\ and\ \lbrack Os(H\sb2)(bpy)\sb2(CO)\rbrack\sp{2+}$ (bpy = 2,2$\sp\prime$-bipyridine; phen = 1,10-phenanthroline) have been prepared by the protonation of the corresponding monocationic hydrides using an excess of trifluoromethanesulfonic acid. The presence of a bound dihydrogen ligand is indicated by short $T\sb1$ minimum values consistent with H-H distances of 0.92-1.04 A. In the partially deuterated derivatives $J\sb{\rm HD}$ values of 25.3-31.0 Hz were observed. The dicationic complexes are strong acids indicating that the bound H$\sb2$ is substantially activated toward heterolytic cleavage. The H$\sb2$ ligand is tightly bound to the metal center, and does not undergo exchange with D$\sb2$ over the course of several weeks at room temperature. The complex $\rm\lbrack Os(H\sb2)(PPh\sb3)\sb2(bpy)(CO)\rbrack\sp{2+}$ has been shown to be very stable in solution at room temperature. In contrast, the ruthenium analogue, $\rm\lbrack Ru(H\sb2)(PPh\sb3)\sb2(bpy)(CO)\rbrack\sp{2+}$ irreversibly loses H$\sb2$ in solution at room temperature but is relatively stable to H$\sb2$ loss at temperatures less than 245 K.The complexes $\rm\lbrack Os(H\sb2)(PPh\sb3)\sb2(bpy)(CO)\rbrack\sp{2+}$ and $\rm\lbrack Os(H\sb2)(PPh\sb3)\sb2(phen)(CO)\rbrack\sp{2+}$ and the corresponding HD complexes were studied by solution NMR spectroscopy in magnetic fields of 11.75 and 17.63 T ($\sp1$H: 500 and 750 MHz). The effects of the partial alignment of these complexes with the magnetic field were large enough to be observable in the NMR spectra. The total splitting of the HD resonance of the partially deuterated complexes was measured in several magnetic fields to determine the field independent spin coupling $(J\sb{\rm HD})$ value and the magnitude and sign of the field dependent residual dipolar coupling $(D\sb{\rm HD}).$