PROTONATION OF METAL-HYDRIDES BY STRONG ACIDS - FORMATION OF AN EQUILIBRIUM MIXTURE OF DIHYDRIDE AND DIHYDROGEN COMPLEXES FROM PROTONATION OF CP-ASTERISK-OS(CO)(2)H - STRUCTURAL CHARACTERIZATION OF [CPW(CO)(2)(PME(3))(PME(3))(H)(2)](-)()OTF()

CpOs(CO)(2)H is protonated by triflic acid (HOTf) in CD2Cl2 solution to give an equilibrium mixture (87:13) of the dihydride [CpOs(CO)(2)( H)(2)](+)OTf(-) and the dihydrogen complex [CpOs(CO)(2)(eta(2)-H-2)]( +)OTf(-). The acidity of these protonated species is roughly comparabl e to HOTf, since only partial protonation was observed, e.g., 36% prot onation with 1.2 equiv of HOTf. In the absence of acid, the T-1 of the hydride ligand of CpOs(CO)(2)H is 5.9 s at -80 degrees C. When all o f the CpOs(CO)(2)H is protonated by excess HOTf, the T-1 (-80 degrees C) of the terminal hydride ligands of [CpOs(CO)(2)(H)(2)](+)OTf(-) i s 2.8 s, while the T-1 of the dihydrogen ligand of [CpOs(CO)(2)(eta(2 )-H-2)](+)OTf(-) is 19 ms (-80 degrees C). The observed T-1 values of the Os-H resonance of CpOs(CO)(2)H decreased significantly under cond itions of partial protonation, indicating intermolecular proton transf er among [CpOs(CO)(2)(eta(2)-H-2)](+)OTf(-), [Cp*Os(CO)(2)(H)(2)](+)O Tf(-), CpOs(CO)(2)H, and HOTf. IR spectra indicate that the two CO li gands of [CpOs(CO)(2)(H)(2)](+) (and hence the hydrides as well) are trans to each other in the four-legged piano stool geometry. Two reson ances for HOTf are observed in the NMR spectra and are assigned as [HO Tf](n) (hydrogen bonded to itself) and TfOH ... OTf(-) in which HOTf i s hydrogen bonded to an OTf(-) counterion. [CpW(CO)(3)(H)(2)](+)OTf(-) and [CpW(CO)(3)(H)(2)](+)OTf(-) were formed by protonation of CpW(CO )(3)H and CpW(CO)(3)H. Protonation of the phosphine-substituted tungs ten 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 dihydr ides [CpW(CO)(2)(PR(3))(H)(2)](+) which were isolated and fully charac terized. The structure of [CpW(CO)(2)(PMe(3))(H)(2)](+)OTf(-) was dete rmined by single-crystal X-ray diffraction and reveals weak hydrogen b onds between one hydride on W and two of the fluorines on the triflate anion.