Calcpeg
ChemaztechSéminaire Chimie ED459
Hydrogen bonding and proton transfer in transition metal hydride chemistry
Dr. Elena Shubina (A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia)
Le Lundi 18 Juin 2012 à 13h45
UM2, salle de cours SC-16.01
Hydrogen bonding and proton transfer to and from transition metal and hydride ligand sites are key steps in many stoichiometric and catalytic chemical and biochemical processes. Being a weak interaction, hydrogen bonding is a good tool to probe the electron density distribution in the molecule ground state. At that its formation is a first, incipient step of proton transfer reaction. In this contribution we will discuss an important role, which hydrogen bonds play in the chemistry of transition metal hydrides. Transition metal hydrides can act as proton donors or proton acceptors in hydrogen bonding.[1, 2] Formation of M–Hδ–···δ+HA or M–Hδ+···B hydrogen bonds entails an additional polarization of an M–H bond and, thus, activates it (tunes its reactivity).[1] At that M–H bonds are easier polarized and more reactive than C–Hδ+ bonds of similar proton donating strength [3] or X–Y bonds of organic bases : proton transfer to or from transition metal hydrides takes place at substantially lower hydrogen bond formation energy.[3, 4] The reaction mechanisms and the possible types of potential energy profiles will be discussed on the basis of experimental and computational results.
The peculiarities of proton transfer between the two transition-metal hydrides with opposite polarities will be also considered. Formation of M–Hδ-···δ+H–M’ dihydrogen bond, detected only recently,[5] precedes the proton transfer and formation of very unusual μ,η1:1–H2 species featuring an end-on coordination mode between the two transition metals. Such complexes could be regarded as models for the heterolytic H2 splitting by transition metal based frustrated Lewis pairs. Finally the examples of the crucial role of weak solute-solvent interactions will be given to discuss the specific and non-specific solvent effects in proton transfer involving transition metal hydrides.
Overall, the knowledge acquired opens the possibility for tuning the reactivity of hydride and dihydrogen complexes and for governing the reaction pathway.
References
1. N. V. Belkova, E. S. Shubina, L. M. Epstein, Acc. Chem. Res. 2005, 38, 624.
2. M. Besora, A. Lledós, F. Maseras, Chem. Soc. Rev. 2009, 38, 957.
3. V. A. Levina, O. A. Filippov, E. I. Gutsul, N. V. Belkova, L. M. Epstein, A. Lledos, E. S. Shubina, J. Am. Chem Soc. 2010, 132, 11234.
4. N. V. Belkova, L. M. Epstein, E. S. Shubina, ARKIVOC, 2008, (iv), 120.
5. V. A. Levina, A. Rossin, N. V. Belkova, M. R. Chierotti, L. M. Epstein, O. A. Filippov, R. Gobetto, L. Gonsalvi, A. Lledós, E.S. Shubina, F. Zanobini, M. Peruzzini, Angew. Chem. Int. Ed. 2011, 50(6), 1367.
Contact local IBMM : Frédéric Lamaty
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