Probing the Structure of the 1:1 Hydrogen-Bonded Complexes of Metallocenes with HCl.

Matrix isolation infrared spectroscopy combined with density functional calculations has been used to form, isolate, and characterize the 1:1 hydrogen-bonded complexes of HCl with ferrocene and ruthenocene. Two unique structures were calculated for each complex, analogous to the two binding sites proposed for the attachment of proton to these metallocenes. The spectra, combined with calculated shifts of the H-Cl stretching mode, support the formation of a complex with the HCl hydrogen bonding to one of the cyclopentadienyl rings, exo to the plane of the ring. Evidence also was obtained for a second structure with the hydrogen of the HCl subunit directed toward the Fe or Ru center between the two cyclopentadienyl rings. This structure is similar to the proposed metal-bound proton structure based on earlier mass spectrometric and computational studies. Importantly, these results were supported by parallel experiments with DCl and the two metallocenes.