Title:	Potential energy surfaces which govern the dynamics of the capture of the primary greenhouse gases and air pollutants by the frustrated Lewis acid/base chemical systems.
DNr:	SNIC 2014/1-153
Project Type:	SNIC Medium Compute
Principal Investigator:	Timofei Privalov <priti@organ.su.se>
Affiliation:	Stockholms universitet
Duration:	2014-05-01 – 2015-05-01
Classification:	10407 10404 10405
Keywords:

Abstract

This is the continuation of the project SNIC 2013/1-137 which has resulted in the discovery of the potentially important dynamical effect in the mechanism of CO2 capture by a representative frustrates Lewis acid/base pair (i.e. tBu3P / B(C6F5)3). The term “frustrated” Lewis pairs (FLPs) is used to describe the stoichiometric mixtures of the Lewis base (LB) and Lewis acid (LA) molecules in which the donor and acceptor atoms are sterically encumbered to such an extent that a fully quenched Lewis adduct cannot be formed; see details in (a) D. W. Stephan, G. Erker, Angew. Chem. Int. Ed., 2010, 49, 46; (b) D. W. Stephan, Org. Biomol. Chem., 2008, 6, 1535;(c) D. W. Stephan, Chem. Commun., 2010, 8526; (e) D. W. Stephan, Dalton Trans., 2009, 3129. The project SNIC 2013/1-137 has had an allocation between 2013-04-19 and 2014-05-01 of 50 x 1000 core-h/month on Triolith at NSC. That resource has been used to compute the multidimensional potential energy surfaces which describe interactions between reactants. The project has been successful. New results are already published in three papers as follows: (a) M. Pu, T. Privalov, Chem. Eur. J., 2013, 14, 16512; (b) M. Pu, T. Privalov, Int. J. Quant. Chem. 2013, 114, 289; (c) M. Pu, T. Privalov, Inorg. Chem., 2014, DOI 10.1021/ic500284q, in press; additionally, a number of manuscripts have been submitted for publications and are at the revision stage. For the continuation, we would like to have an increase of the computational time up to 75 x 1000 core-h/month on Triolith at NSC because an essential part of the planned work will involve calculations of PES of {LB + X + LA} systems using the solute – solvent cluster models with up to 100 solvent molecules (e.g. toluene) representing first solvation shells of the reacting and early van der Waals (vdW) complexes; here X = CO2, N2O and SO2 as well as other “small” molecules. Thus far obtained results are very promising but indicate that we have only scratched the surface, we now aim to systematically carry out quantum-chemical analysis of frustrated Lewis acid/base pairs (FLPs) and their use in important areas of modern chemistry such as sequestration of the primary greenhouse gases (e.g. CO2 and N2O) and dangerous air pollutant SO2, heterolytic cleavage of H2 and the metal-free catalysis of hydrogen-transfer. These areas are of considerable interest at present and it is most certain that they will remain scientifically relevant for quite some time. The scientific question, that we are concerned with, is about the role of the intra- and inter-molecular motion, i.e. molecular vibrations and the relative motion of reactants, that can occur at the femtosecond to picosecond timescales while molecules (reactants) collide and chemically interact at finite (non-zero) temperature in gas and condensed phases. The synergistic combination of two methodologies - the ab initio molecular dynamics (AIMD) and the minimum energy pathway (MEP) mapping of the potential energy surfaces (PESs) - should lead to new fundamental insights. Results from our recent studies indicate high scientific potential of the planned work. The planned research should significantly expand boundaries of current knowledge about dynamical effects in chemical reactions and produce accurate quantitative predictions that will guide future experiments. Naturally, a key part of the planned work will be the minimum energy (MEP) mapping of the potential energy surfaces (PESs) and investigation of the properties of the low-dimensional projections (cuts) of PESs for reaction between FLPs and small molecules such as CO2, N2O and SO2. Details of our approach could be found in [M. Pu, T. Privalov, Inorg. Chem., 2014, DOI 10.1021/ic500284q and M. Pu, T. Privalov, Int. J. Quant. Chem. 2013, 114, 289]. While high level AIMD trajectory simulations will be carried out using in-house computers, the MEP mapping of PESs will be carried out using resources at NSC. As our recently published results show, this an efficient approach which accurately reveals details about an involvement of nuclear motion (molecular vibrations) during the reaction and the mechanistic consequences of the time-dependence of the donor-acceptor interactions in the reacting complexes. Specifically, the planned work will involve the PES/MEP analyses of (i) CO2, N2O and SO2 capture by representative FLPs with diverse chemical structures; (ii) the dissociation pathways of the LB-C(O)O-LA adducts; (iii) PES-related properties of dative bonds in adducts of FLPs with CO2, N2O and SO2.