Computational Design of Bidentate Hypervalent Iodine Catalysts in Halogen Bond-Mediated Organocatalysis

In recent years, halogen bond-based organocatalysis has garnered significant attention as an alternative to hydrogen-based catalysis, capturing considerable interest within the scientific community. This transition has witnessed the evolution of catalytic scaffolds from monodentate to bidentate architectures, and from monovalent to hypervalent species. In this DFT-based study, we explored a bidentate hypervalent iodine(III)-based system that has already undergone experimental validation. Additionally, we explore various functionalisations (-CF3, -CH3, -tBu, -OH, -OMe, -NO2, -CN) and scaffold modifications, such as sulfur oxidation, theoretically proposed for an indole-based Michael addition. The investigated systems favour bidentate O-type binding, underlining the importance of ligand coordination in catalytic activity. Electron-deficient scaffolds exhibited stronger binding and lower activation energies, indicating the pivotal role of electronic properties for σ-hole-based catalysis. Of these groups, Lewis-base-like moieties formed stabilising intramolecular interactions with hypervalent iodines when in the ortho-position. Furthermore, inductive electron withdrawal was deemed more effective than mesomeric withdrawal in enhancing catalytic efficacy for these systems. Lastly, increasing sulfur oxidation was theoretically proven to improve catalytic activity significantly.

Halogen Bond Catalysis: A Physical Chemistry Perspective

As important noncovalent interactions, halogen bonds have been widely used in material science, supramolecular chemistry, medicinal chemistry, organocatalysis, and other fields. In the past 15 years, halogen bond catalysis has become a developed field in organocatalysis for the catalysts' advantages of being environmentally friendly, inexpensive, and recyclable. Halogen bonds can induce various organic reactions, and halogen bond catalysis has become a powerful alternative to the fully explored hydrogen bond catalysis. From a physical chemistry view, this perspective provides an overview of the latest progress and key examples of halogen bond catalysis via activation of the lone pair systems of organic functional group, π systems, and metal complexes. The research progresses in halogen bond catalysis by our group were also introduced.

Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

In this work, the pK_a values of 69 polar alkanes (YH₂) in acetonitrile were computed using the method developed by Luo and Zhang in 2020, and representative 69 thermodynamic network cards on 22 elementary steps of YH₂ and related polar alkenes (Y) releasing or accepting H₂ were naturally established. Potential electron reductants (YH^-), hydride reductants (YH^-), antioxidants (YH₂ and YH^-), and hydrogen molecule reductants (YH₂) are unexpectedly discovered according to thermodynamic network cards. It is also found that there are great differences between YH₂ and common hydrogen molecule reductants (XH₂), such as Hantzsch ester (HEH₂), benzothiazoline (BTH₂), and dihydro-phenanthridine (PH₂), releasing two hydrogen ions to unsaturated compounds. During the hydrogenation process, XH₂ release hydrides first, then the oxidation state XH⁺ release protons. However, in the case of YH₂, YH₂ release protons first, then YH^- release hydrides. It is the differences on acidic properties of YH₂ and XH₂ that result in the behavioral and thermodynamic differences on YH₂ and XH₂ releasing two hydrogen ions (H^--H⁺). The redox mechanisms and behaviors of Y, YH^-, and YH₂ as electron, hydrogen atom, hydride, and hydrogen molecule donors or acceptors in the chemical reaction are reasonably investigated and discussed in this paper using thermodynamics.