Protonation of metal hydrides by strong acids. Formation of an equilibrium mixture of dihydride and dihydrogen complexes from protonation of Cp*Os(CO)(2)H. Structural characterization of [CpW(CO)(2)(PMe(3))(PMe(3))(H)(2)](+)OTf(-)

Cp*Os(CO)(2)H is protonated by triflic acid (HOTf) in CD2Cl2 solution to give an equilibrium mixture (87:13) of the dihydride [Cp*Os(CO)(2)(H)(2)](+)OTf(-) and the dihydrogen complex [Cp*Os(CO)(2)(eta(2)-H-2)](+)OTf(-). The acidity of these protonated species is roughly comparable to HOTf, since only partial protonation was observed, e.g., 36% protonation with 1.2 equiv of HOTf. In the absence of acid, the T-1 of the hydride ligand of Cp*Os(CO)(2)H is 5.9 s at -80 degrees C. When all of the Cp*Os(CO)(2)H is protonated by excess HOTf, the T-1 (-80 degrees C) of the terminal hydride ligands of [Cp*Os(CO)(2)(H)(2)](+)OTf(-) is 2.8 s, while the T-1 of the dihydrogen ligand of [Cp*Os(CO)(2)(eta(2)-H-2)](+)OTf(-) is 19 ms (-80 degrees C). The observed T-1 values of the Os-H resonance of Cp*Os(CO)(2)H decreased significantly under conditions of partial protonation, indicating intermolecular proton transfer among [Cp*Os(CO)(2)(eta(2)-H-2)](+)OTf(-), [Cp*Os(CO)(2)(H)(2)](+)OTf(-), Cp*Os(CO)(2)H, and HOTf. IR spectra indicate that the two CO ligands of [Cp*Os(CO)(2)(H)(2)](+) (and hence the hydrides as well) are trans to each other in the four-legged piano stool geometry. Two resonances for HOTf are observed in the NMR spectra and are assigned as [HOTf](n) (hydrogen bonded to itself) and TfOH ... OTf(-) in which HOTf is hydrogen bonded to an OTf(-) counterion. [CpW(CO)(3)(H)(2)](+)OTf(-) and [Cp*W(CO)(3)(H)(2)](+)OTf(-) were formed by protonation of CpW(CO)(3)H and Cp*W(CO)(3)H. Protonation of the phosphine-substituted tungsten hydrides CpW(CO)(2)(PR(3))H (R = Me, Cy, Ph) by HOTf or [H(Et(2)O)(2)](+) BAr'(-)(4) (Ar' = 3,5-bis(trifluoromethyl)phenyl) gives dihydrides [CpW(CO)(2)(PR(3))(H)(2)](+) which were isolated and fully characterized. The structure of [CpW(CO)(2)(PMe(3))(H)(2)](+)OTf(-) was determined by single-crystal X-ray diffraction and reveals weak hydrogen bonds between one hydride on W and two of the fluorines on the triflate anion.