Abstract
The strong, specific, and directional halogen bond (XB) is an ideal supramolecular synthon in crystal engineering, as well as rational catalyst and drug design. These attributes attracted strong growing interest in halogen bonding in the past decade and led to a wide range of applications in materials, biological, and catalysis applications. Recently, various research groups exploited the XB mode of activation in designing halogen-based Lewis acids in effecting organic transformation, and there is continual growth in this promising area. In addition to the rapid advancements in methodology development, computational investigations are well suited for mechanistic understanding, rational XB catalyst design, and the study of intermediates that are unstable when observed experimentally. In this review, we highlight recent computational studies of XB organocatalytic reactions, which provide valuable insights into the XB mode of activation, competing reaction pathways, effects of solvent and counterions, and design of novel XB catalysts.
Highlights
Halogen bonding attracted growing interest in recent years, due to its wide range of applications as highly directional motifs in supramolecular chemistry, crystal engineering, materials science, organocatalysis, and drug design [1]
Bickelhaupt and co-workers applied this state-of-the-art method in a recent computational study on halogen bond organocatalysis [49]
Results from SMD modeling of common organic solvents chloroform and n-hexane showed that free energy of activation for both uncatalyzed and CAT-3-perFPhI-catalyzed reactions increases compared to the gas-phase results, and the catalyzed reaction is still faster in both solvents
Summary
Halogen bonding attracted growing interest in recent years, due to its wide range of applications as highly directional motifs in supramolecular chemistry, crystal engineering, materials science, organocatalysis, and drug design [1]. The σ-hole concept of Politzer et al [3,4] represents the most widely accepted model to explain the origin of the halogen bond In this model, the halogen atom is characterized by anisotropic distribution of electron density with a localized region of positive electrostatic potential (ESP) along the extension of the R–X bond (Figure 1). The halogen atom is characterized by anisotropic distribution of electron density with a localized region of positive electrostatic potential (ESP) along the extension of the R–X bond (Figure 1) This model readily accounts for the close contact between halogen and nucleophile (Nu), as well as the linearity of the R–X . The stronger frontier orbital interaction derives from the lower energy of the σ* LUMO of R–X
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