Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3)

Natalia V. Belkova, Maria Besora, Lina M. Epstein, Agustí Lledós, Feliu Maseras, Elena S. Shubina

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Abstract

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy3) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF3)3COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (η2-H2)-complex 3 (ΔH‡ = 11.0 ± 0.5 kcal/mol and ΔS‡ = -19 ± 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF3COOH and (CF3)3COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR]- in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy3)(η2-H2)]+ is driven by the formation of the homoconjugated anionic complex [ROHOR]-. Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy3), observed at temperatures above 250 K.
Original languageEnglish
Pages (from-to)7715-7725
JournalJournal of the American Chemical Society
Volume125
Issue number25
DOIs
Publication statusPublished - 25 Jun 2003

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