Computational studies of chemical reaction mechanisms with explicit participation of solvent
Recently, experiment indicated involvement of ethereal solvent molecules (dioxane, THF etc) as Lewis bases (LBs) in the Lewis acid (LA) catalyzed hydrogenation of ketones/aldehydes with H2 – for example, [Scott, D. J.; Fuchter, M. J.; Ashley, A. E. J. Am. Chem. Soc. 2014, 136, 15813-15816] and [Scott, D. J.; Fuchter, M. J.; Ashley, A. E. J. Am. Chem. Soc. 2014, 136, 15813-15816] and the work that followed. In this project, we will continue the line of research charted by our recent articles such as [Hesmat, M.; Privalov, T; J. Chem. Phys. 2017, DOI: 10.1063/1.4999708, in press], Hesmat, M.; Privalov, T; J. Chem. Phys. 2017, 2017, 014303], [Hesmat, M.; Privalov, T Chem. Eur. J., 2017, in press, DOI: 10.1002/chem.201700937] and [Hesmat, M.; Privalov, T, Chem. Eur. J., 2017, 23, 9098; DOI: 10.1002/chem.201700437]. In comparison to the majority of nowadays known examples of the heterolytic H2-splitting by the so-called Frustrated Lewis Pairs (FLPs), mechanistic analysis of reactions involving borane Lewis acids, e.g. B(C6F5)3, in ethereal solvent is more complicated because of Lewis acid complexation of solvent, substrate and water. There can be multitude of possible pathways, as indicated in our recent articles, and such pathways and their competition is what we will computationally study in this project.In 2009, we published results describing B(C6F5)3-catalyzed hydrogenation of ketones/aldehydes and suggesting for the first time that an FLP mechanism analogous to that for the related hydrogenation of imines (and hydrosilylation of carbonyl compounds) should be kinetically accessible. Our prediction was based on simplified (continuum) treatment of solvent. However, we suspected that solvent might take part explicitly in the reaction mechanism – for example, suitably basic solvent taking part in the proton transfer step. Our idea of B(C6F5)3-catalyzed hydrogenation of carbonyl compounds (C=O bonds) have sparked significant interest internationally and our intuition regarding direct involvement of solvent is now confirmed by experiment – the aforementioned articles by Stephan et al. and Ashley et al. plus the work of others that followed. In a few words, the goal now is to investigate possible mechanistic scenarios of solvent involvement including direct involvement of solvent in the proton-transfer step as LA-acceptor – details of possible mechanisms can be found in the introductory sections of our recently published articles. This work will provide foundation for collaboration with experiment.