Gleb A. Silantyev, Oleg A. Filippov, Peter M. Tolstoy, Natalia V. Belkova, Lina M. Epstein, Klaus Weisz, Elena S. Shubina
"Hydrogen bonding and proton transfer to ruthenium hydride complex CpRuH(dppe): metal and hydride dichotomy"
Inorganic Chemistry, 2013
Abstract:
The combination of variable temperature (190-297 K) IR and NMR spectroscopy studies with quantum-chemical calculations at the DFT/B3PW91 and AIM level had the aim to determine the mechanism of proton transfer to CpRuH(dppe) (1, dppe = Ph2P(CH2)2PPh2) and the structures of intermediates. Dihydrogen bond (DHB) formation was established in the case of interaction with weak proton donors like CF3CH2OH. Low-temperature protonation (at about 200 K) by stronger proton donors leads via DHB complex to cationic non-classical complex [CpRu(η2-H2)(dppe)]+ (2). Thermodynamic parameters of DHB formation (for CF3CH2OH: deltaH° = -4.9 ± 0.2 kcal·mol-1, deltaS° = -17.8 ± 0.7 cal·mol-1·K-1) and proton transfer (for (CF3)2CHOH: deltaH°PT = -5.2 ± 0.3 kcal·mol-1, deltaS°PT = -23 ± 1 cal·mol-1·K-1) were determined. Above 240 K 2 transforms into trans-[CpRu(H)2(dppe)]+ (3) yielding a mixture of 2 and 3 in 1:2 ratio. Kinetic analysis and activation parameters for “[Ru(η2-H2)]+ → trans-[Ru(H)2]+” transformation indicate reversibility of this process in contrast to irreversible intramolecular isomerization of Cp* analogue. Calculations show that the driving force of this process is greater stability (by 1.5 kcal·mol-1 in deltaE scale) of the dihydride cation in comparison with the dihydrogen complex. The calculations of the potential energy profile indicate the low barrier for deprotonation of 2 suggesting that the formation of trans-[CpRu(H)2(dppe)]+ proceeds via deprotonation of [Ru(η2-H2)]+ to DHB complex, formation of hydrogen bond with Ru atom and subsequent proton transfer to the metal site.