Romulo ANDO1, Leandro MARQUES1, Shannon MCLAUGHLIN2, Malgorzata SWADZBA-KWASNY2
1University of São Paulo, São Paulo, Brazil
2Queen`s University Belfast, Belfast, Ireland
Frustrated Lewis Pairs (FLPs) have been largely investigate due to their catalytic potential to split and activate small molecules.[1] FLPs rely on a Lewis acid-base pair sterically hindered to form a classical Lewis adduct in solution, they can be formed by intramolecular Lewis pairs or by intermolecular ones. Intermolecular FLPs have attracted much attention due to the variety of possible combinations between Lewis acids and Lewis bases that can be originated, yet, these FLPs are versatile for reacting with small molecules, as the Lewis acid-base pair have some flexibility when they are close to each other. However, the main difficulty to achieve this reactivity is increasing the population of encounter complexes, that is, shift the equilibrium to maintain the Lewis acid-base pair close enough to give rise a reactive cavity between the acidic and the basic Lewis atoms.[2] One approach to enhance these complexes is to change the medium, so instead of using conventional solvents, using ionic liquids (ILs) have demonstrated to increase the encounter complexes population.[3] In addition, some Lewis acid-base pairs have been observed to act as FLPs even forming the respective classical Lewis adducts, as they can split hydrogen and activate CO2. These Lewis pairs show an accessible frustration in the equilibrium between the Lewis adduct and the free species, therefore they show FLP reactivity.
Thereby, motivated by using ILs as solvents, this work aims to investigate FLP-ILs systems formed by the combination of the B(C6F5)3 Lewis acid and the tricyanomethanide (TCM) based ILs ([Cnmim][TCM], n=2,4,6,8). This system benefits to have the [TCM]– anion as a Lewis base, in this way, the Lewis pair B(C6F5)3/[TCM]– formed in the ionic liquid can exhibit FLP reactivity. Vibrational spectroscopy and, 11B and 13C NMR characterization along with DFT calculations of the Lewis pair showed that the main geometry is stabilised by a Lewis adduct between the [TCM]– anion and the B(C6F5)3. The figure below shows IR and NMR spectra for the B(C6F5)3 in [C8mim][TCM]. These FLP-ILs system will be studied for the capability to activate hydrogen and subsequent catalyse hydrogenations of model olefins.
[1] D. W. Stephan, J Am Chem Soc 2021, 143, 20002-20014.
[2] A. R. Jupp, Dalton Trans 2022, 51, 10681-10689.
[3] L. C. Brown, J. M. Hogg, M. Gilmore, L. Moura, S. Imberti, S. Gartner, H. Q. N. Gunaratne, R. J. O'Donnell, N. Artioli, J. D. Holbrey, M. Swadzba-Kwasny, Chemical Communications 2018, 54, 8689-8692.