Pnictogen, chalcogen, and halogen bonds in catalytic systems: theoretical study and detailed comparison

Although halogen bond (XB), a typical σ-hole noncovalent interaction, has been widely exploited in organocatalysis within the last two decades, only very recently has its sister σ-hole interactions, such as chalcogen bond (ChB) and pnictogen bond (PnB), begun to be explored for potential applications in catalysis. Herein, a detailed comparison investigation of PnB, ChB, and XB interactions in catalytic systems was performed from a theoretical point of view. Owing to the excellent properties of the pentafluorophenyl moiety (C₆F₅) in catalysis, the complexes of (C₆F₅)₃Pn, (C₆F₅)₂Ch, and C₆F₅X with chloride ion were firstly studied. Then, we successively substituted C₆F₅ by phenyl groups, to examine the influence of substituents on the characteristics of such interactions. In addition, several halogen-bonded complexes between the donor 1,3,5-trifluoro-2,4,6-triiodobenzene (C₆F₃I₃) and heavier Pn and Ch species as acceptors were also investigated. Our calculations showed that the interactions become gradually stronger upon going from row 3 to 5 and from main group VII to V, which correlates well with the experimental observations. As the strength of the interactions enhances, the contribution of electrostatics to the attraction increases, while the orbital term contribution becomes smaller. Particularly, the significant differences between the three types of σ-hole interactions found in catalysis and anion transport were clarified.