Cp*Os(CO)2H 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(η2-H2)] +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 T1 of the hydride ligand of Cp*Os(CO)2H is 5.9 s at -80°C. When all of the Cp*Os(CO)2H is protonated by excess HOTf, the T1 (-80°C) of the terminal hydride ligands of [Cp*Os(CO)2(H)2]+OTf- is 2.8 s, while the T1 of the dihydrogen ligand of [Cp*Os(CO)2(η2-H2)] +OTf- is 19 ms (-80°C). The observed T1 values of the Os-H resonance of Cp*Os(CO)2H decreased significantly under conditions of partial protonation, indicating intermolecular proton transfer among [Cp*Os(CO)2(η2-H2)] +OTf-, [Cp*Os(CO)2(H)2]+OTf-, Cp*Os(CO)2H, 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)3H and Cp*W(CO)3H. Protonation of the phosphine-substituted tungsten hydrides CpW(CO)2(PR3)H (R = Me, Cy, Ph) by HOTf or [H(Et2O)2]+ BAr′4- (Ar′ = 3,5-bis(trifluoromethyl)phenyl) gives dihydrides [CpW(CO)2(PR3)(H)2]+ which were isolated and fully characterized. The structure of [CpW(CO)2(PMe3)(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.
|Number of pages||13|
|Publication status||Published - May 14 1996|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry