Competition between the Hydride Ligands of Two Types in Proton Transfer to [{kappa(3)-P-CH3C(CH2CH2PPh2)(3)}RuH(eta(2)-BH4)]

The interaction of the mixed hydrido-tetrahydridoborate ruthenium(II) complex [(Triphos) RuH(eta(2)-BH4)] [1; Triphos =kappa(3)-P-CH3C(CH2CH2PPh2)(3)] with alcohols of variable acidic strength [MeOH, FCH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)(2)CHOH (HFIP), and (CF3)(3)COH (PFTB)] was the subject of a combined computational (DFT) and spectroscopic (VT FTIR, NMR) study. The experimental spectra suggests that RuH center dot center dot center dot HO bond formation precedes the protonation of 1, and H-2 evolution leads to the loss of boron and the formation of the dimetal-lic [{(Triphos) RuH}(2)(mu,eta(2):eta(2)-BH4)](+) cation. The experimentally determined basicity factor [Ej(RuH)] of the Ru-bound hydrido ligand of 1.43 is among the highest determined for ruthenium hydrides. Such high basicity leads to very easy proton transfer to the RuH ligand for strong alcohols (HFIP and PFTB). An alternative reaction pathway involving the migration of the bridging hydride (BHbr) to the ruthenium center is suggested for weaker proton donors (MeOH and TFE).