Directionality of Dihydrogen Bonds: The Role of Transition Metal Atomsстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 марта 2017 г.
Аннотация:A theoretical study on two series of electron-rich group 8 hydrides is carried out to evaluate involvement of the transition metal in dihydrogen bonding. To this end, the structural and electronic parameters are computed at the DFT/B3PW91 level for hydrogen-bonded adducts of [(PP3)MH2] and [Cp*MH(dppe)] (M=Fe, Ru, Os; PP3=?4-P(CH2CH2PPh2)3, dppe= ?2-Ph2PCH2CH2PPh2) with CF3CH2OH (TFE) as proton donor. The results are compared with those of adduct [Cp2NbH3]center dot TFE featuring a pure dihydrogen bond, and classical hydrogen bonds in pyridine center dot TFE and Me3N center dot TFE. Deviation of the H center dot center dot center dot H-A fragment from linearity is shown to originate from the metal participation in dihydrogen bonding. The latter is confirmed by the electronic parameters obtained by NBO and AIM analysis. Considered together, orbital interaction energies and hydrogen bond ellipticity are salient indicators of this effect and allow the MH center dot center dot center dot HA interaction to be described as a bifurcate hydrogen bond. The impact of the M center dot center dot center dot HA interaction is shown to increase on descending the group, and this explains the experimental trends in mechanisms of proton-transfer reactions via MH center dot center dot center dot HA intermediates. Strengthening of the M center dot center dot center dot H interaction in the case of electron-rich 5d metal hydrides leads to direct proton transfer to the metal atom.