Monocyclopentadienylhydride Derivatives of Ruthenium: Stereoselective Proton Transfer and Proton-Hydride Exchange in an Extremely Short Dihydrogen Bond

Diastereomerically pure complexes of formula CpRuCl(PP*) and CpRuH(PP*) with chiral ferrocenyl
diphosphines were prepared and the selectivity of proton-transfer processes over the monohydride
compounds with different acids was studied. With 1 equiv of HBF4 the cis-dihydrogen and trans-dihydride
complexes were formed while with 3 equiv of CF3CO2H the trans-dihydride derivative was the only product.
However, the use of 1 equiv of CF3CO2H led to a dihydrogen bonded complex with an extremely short
RuH···HO2CF3 interaction that exhibits proton-hydride exchange. Using the labeled acid CF3CO2D, a
stereoselective transference of the deuteron was demonstrated that implies the previous epimerization of
the monohydride and the subsequent attack of the acid in the position previously occupied by the hydride.