Ruthenocene protonation

Another interesting comparison of Group VIII metallocenes concerns their ease of protonation in boron trifluoride hydrate (14). It appears that the proton is attached directly to the metal atom, and that ruthenocene and osmocene are protonated to a lesser extent than ferrocene. 

RT, the protonation equilibrium constant is 203 M for RhCKCOCAsPhj) it is 75 M. Similar K values are found for Ir and Rh complexes with phosphine and halide ligands. Finally, ruthenocene is half-protonated in H SO with an acidity function, Hg, of —5.7, whereas half-protonation of ferrocene requires an Hg of —7.7. 

H NMR spectra (DMSO-dg) of the Ag" complexes of ruthenocenophanes (81) and (82) suggest no interaction between the ruthenium and the complexed silver ion. In this case, the methylene protons attached to sulfur atoms were shifted more than the protons of the ruthenocene nucleus. H NMR spectra of the mercury(II) complexes of (80)-(82) suggest that there is signihcant interaction between ruthenium and the mercury(II). The P protons of the Cp rings were shifted further downfield than the a protons, and the ethylene protons exhibited very little downfield shift <85BCJ3540>. 

The density functional approach has been used in an investigation of the protonation of ferrocene, ruthenocene, and osmocene in the gas phase, and the general conclusion is that the addition of a proton to the carbon atoms in the cyclopentadienyl ring is favored in ferrocene, whereas metal protonation is favored with ruthenocene and osmocene. The results obtained from these calculations were used in the interpretation of electrophilic substitution reactions of metallocenes. The basicity of the ligand group l,l -bis(diphenylphosphino)metallocene has also been examined. This is an important aspect for catalysis because it has proved difficult to obtain results which... 

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