Protonation of Cp*M(dppe)H Hydrides: Peculiarities of the Osmium Congenerстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 18 марта 2017 г.
Аннотация:The interaction between Cp*OsH(dppe) (1) and a series of proton donors (HA) of increasing strength [indole, CFH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)(2)CHOH (HFIP), p-nitrophenol, and HBF4 center dot Et2O] has been investigated experimentally by variable temperature IR and NMR spectroscopy in solvents with different coordinating abilities (alkanes, dichloromethane and their mixtures) and computationally at the DFT/B3PW91 level using different models. Both the IR and NMR spectroscopic data for the interaction with weak proton donors conform to the criteria of M-H center dot center dot center dot H-A bond formation. Theoretical calculations, however, indicate an asymmetric bifurcated interaction with a significant contribution from the metal atom, which is greater than that previously found for the corresponding Fe system. The basicity factor of 1 (E-j = 1.47) is greater than those of the Ru (1.39) and Fe (1.35) congeners, in agreement with previous studies on other compound families. The kinetic product of proton transfer, cis-[Cp*Os(H)(2)(dppe)]*X-, which is selectively obtained at low temperatures, irreversibly rearranges to trans[Cp*Os(H)(2)(dppe)]X-+(-) upon warming to >230K. The latter compound with X = BF4 has been crystallographically characterized. The activation enthalpy of the isomerization process (Delta H-not equal = 21.5 +/- 1.0 kcal mol(-1)), obtained from kinetics investigation by H-1 NMR in the 240-260 K range, is identical within experimental error to those previously reported for the M(eta(2)-H-2)+BF4- -> trans-M(H)(2)+BF4- isomerization process of the iron and ruthenium analogues. The activation entropy (Delta S-not equal = 12 +/- 4 e.u.), on the other hand, is greater than for the lighter metals, following the order Fe < Ru < Os. The mechanism of proton transfer and trends in the energetics of the various steps upon changing the nature of the metal atom are discussed.