Upgrade of Weak σ-Hole Bond Donors via Cr(CO) Complexation.

Molecular recognition mediated by σ-hole interactions is enhanced as the electrostatic potential at the σ-hole becomes increasingly positive. Traditional methods to strengthen σ-hole donor ability of atoms such as halogens often involve covalent modifications, such as, introducing electron-withdrawing substituents (neutral or positively charged) or electrochemical oxidation. Metal coordination, a relatively underexplored approach, offers a promising alternative. In this study, η-coordination of Cr(CO) to haloarenes, a neutral system, is demonstrated to significantly increase the electrophilic character of halogen bond donors, enabling weak donors such as chloroanisole to form short and directional Cl⋅⋅⋅O halogen bonds. Structural characterization using single-crystal X-ray diffraction and computational analysis of a series of η-Cr(CO)-coordinated haloarenes provides evidence for this enhancement. Furthermore, the effect is shown to extend to other heteroatomic substituents on the coordinated arene, e. g., other halogen atoms as well as elements of groups 16, 15, and 14 of the periodic table, broadening the scope of this approach.