Stabilization of encounter complexes of intermolecular frustrated Lewis pairs by dispersion energy donors

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Dispersion interactions have now been identified in all fields of chemical research giving rise to unusual physical properties, conformations, selectivity of reactions and stabilization of overcrowded molecules. One of the most fascinating aspects is that steric bulk in the form of dispersion energy donors can also lead to the thermodynamic stabilization of molecules resulting in spectacular bonding situations or in extremely short intermolecular distances.This research project focusses on the exploitation of dispersion energy donors for the stabilization of the encounter complexes of intermolecular frustrated Lewis pairs. The triaryl derivatives of phosphorus, nitrogen and boron derived Lewis bases and Lewis acids will be equipped in 3 and 5 position of the aromatic rings with dispersion energy donors. Rigid alkyl fragments such as methyl, isopropyl and tertbutyl will provide the necessary dispersion energy to stabilize the corresponding encounter complex of the Lewis acid and Lewis base. All in all, 54 combinations of dispersion energy stabilized encounter complexes are available, which will be investigated by nuclear-Overhauser enhanced NMR spectroscopic methods. The directionality of the corresponding intermolecular interactions will be analyzed offering the elaboration of solution structures. Furthermore, the association constants will be determined at different temperatures enabling for the determination of the thermodynamic parameters. Furthermore, the activity of the frustrated Lewis pairs in the hydrogen splitting will be investigated connecting dispersion stabilization of the encounter complexes to catalytic activity. The experimental data is of high value for the quantum mechanical description of dispersion interactions offering the improvement of accuracy of dispersion-corrected density functional theory. Our synthetic investigations will be complemented by quantum-mechanical calculations in strong collaboration with S. Grimme. The structure of each of the Lewis acid and Lewis base will be optimized by DFT-based methods and subsequent energy decomposition analysis will specify the role of the various energy contributions. Ultimately, this provides a qualitative and quantitative analysis of interacting dispersion energy donors on a highly systematic level. In summary, this approach to dispersion energy donor-stabilized encounter complexes of Lewis pairs strongly connects to all of the key-topics of the SPP 1807: - synthesis of novel dispersion energy donor -stabilized structure- quantitative evaluation of dispersion energy donors in connection with intermolecular complexation,- solvent dependency of dispersion energy donor-stabilized structures and- transition-state stabilization through dispersion energy donors