(Pre)association as a crucial step for computational prediction and analysis of the catalytic activity of σ-hole donating organocatalysts

Abstract

Based upon the experimentally obtained kinetic data on iodonium salt catalyzed nucleophilic addition of isocyanide to imine leading to imidazopyridine species, a reliable model for DFT calculations has been suggested....

Solvent-modulated binding selectivity of reaction substrates to onium-based σ-hole donors

“…- ------------------------------------------------In this work, we have decided to shift the focus of the discussion from the nature of electrophilic activation to the less obvious but, possibly, more important binding factor. Recently we have suggested a reliable model for the consideration of the binding process during DFT calculations 48 , and here we apply this model to the estimation of the solvent effects for the systems involving onium salt catalysis to shed light on how the nature of the solvent affects the equilibrium concentration of reactive catalystelectrophile associates. Based upon the experimental and theoretical study on the catalytic activity of a series of onium salts in different solvents, the discussion of the factors affecting their catalytic activity related to the binding processes is represented.…”

“…Density functional theory calculations for determination of the relative binding energies. For computational analysis of the Cat + substrate association process, we have used the model suggested by us previously, 48 because it gave the results similar to the experimentally obtained binding energies. This model presupposes the involvement of two solvent molecules taken in the explicit form in the computations: one ligated to the catalyst -hole and the other bound to the nucleophilic part of a reaction substrate (Figure 3).…”

Cooperative Catalysis Involving Hydrogen and Halogen Bond Donors: A Computational Study on the Thiourea–Iodonium System

“…[47][48][49] We have chosen this functional according to our previous experience and its successful performance in a number of halogen and chalcogen bonds studies in various similar supramolecular systems and organocatalysis processes. 40,42 The quasi-relativistic MWB46 pseudopotentials, 50 which described 46 core electrons, and the appropriate contracted basis sets were used for iodine atoms, while the standard 6-31G* basis sets were used for other atoms. No symmetry restrictions were applied during the geometry optimizations.…”

“…The cyclic form of cations (5*-7*) stabilized by intramolecular XB between the I and S atoms is more stable than the corresponding open-chain form (5-7) by 30-37 kJ mol -1 in ∆G scale in the absence of the solvent, but the energy gap is expected to be significantly lower in the case of consideration of ligated solvent molecules taken in explicit form. 42 Taking into account significant inaccuracy in the relative energy between two forms of the catalysts in real systems, further they are discussed separately. For binding of 5-7 and 5*-7* with TS, no solvent molecules have been discussed since the general idea of this work is to compare relative energy between the associates and the solvation effects were expected to be very similar for the same functionalities in the selected species.…”

“…And vice versa, occupation of one of the -holes by the electron-donating species should result in decrease of the catalytic activity of the iodonium moiety. 29,42 These suggestions are coherent with our estimation of the values of maximum electrostatic potentials [Vs(max)] on the corresponding atoms: 480-515 kJ mol -1 on the -holes of the I atom in 5-7 vs 445-465 kJ mol -1 on that of 5*-7*, and 475-525 kJ mol -1 on the amide H atoms of 5-7 vs 515-535 kJ mol -1 for 5*-7*. In addition, the IS interactions in 5*-7* are accompanied by a charge transfer from the lone pair of the S atom to the antibonding I-C orbitals equal to 56-81 kJ mol -1 (namely 81 kJ mol -1 for 5*, 60 kJ mol -1 for 6*, 56 kJ mol -1 for 7*, according to second order perturbation theory analysis of Fock matrix in natural bond orbitals basis), which has moderate 41,43 value for such type interactions.…”