Specific and non-specific influence of the environment on dihydrogen bonding and proton transfer to [RuH2{P(CH2CH2PPh2)3}]

The proton transfer from substituted phenols (ArOH = p-nitrophenol, p-nitophenyl-aza-phenol) to the ruthenium dihydride complex [(PP3)RuH2], where PP3 = P(CH2CH2PPh2)3, was studied by variable temperature UV–visible spectroscopy in dichloromethane, THF, THF/CH3OH and THF/CH3CN mixtures, showing a significant influence of the polarity and/or the proton donating/proton accepting properties of the solvent on the position of the proton transfer equilibrium. The formation of ion pairs stabilized by hydrogen bonding between the non-classical cation [(PP3)RuH(η2-H2)]+ and the homoconjugated anion [ArOHOAr]− was determined in low-polar media. The increase of the media polarity has been proved to favor the proton transfer leading to the dissociation of hydrogen bonded ion pairs [{(PP3) RuH(η2-H2)}+⋯{ArOHOAr}−]. Under comparable media polarity, the presence of a protic solvent in the mixture greatly favors the proton transfer due to the additional H-bonding with solutes. The structural, energetic and electronic features of the dihydrogen bonded adducts and of the proton transfer products were investigated by means of DFT/B3LYP calculations on the model dihydride [{P(CH2CH2PH2)3}RuH2] using CH3OH or CF3OH as proton donors. The specific and non-specific influence of the media properties on the dihydrogen bonding and proton transfer was studied by introducing the second protic (proton donor or solvent) molecule in the model system or by CPCM calculations. The additional participation of external molecules, from either the solvent or the alcohol, strengthens remarkably the dihydrogen bonded adducts and eases the proton transfer process.