Redox Activation of Halogen-Bonding Catalysts for Organic Synthesis

Abstract

Among non-covalent interactions, halogen bonding (XB) has emerged as a sophisticated tool for molecular assembly and catalysis, distinguished from its hydrogen bonding (HB) analogues by its superior directionality and the high polarizability of the halogen atom. These characteristics offer unique opportunities for fine-tuning the strength and the geometry of this interaction to achieve targeted functionalities. Furthermore, the use of a redox-active moiety enables a controlled increase of the XB donor strength upon oxidation, effectively activating the XB donor catalyst. Herein, we report the rational design and the synthesis of ferrocene-based XB donors. Characterization of the fundamental XB interactions in the system was performed through a synergistic approach involving single-crystal X-ray diffraction and solution-phase binding studies. Density Functional Theory (DFT) analysis reveals a significant amplification of the 'σ-hole' intensity upon oxidation, a feature we exploit to drive catalytic turnover. Notably, these redox-switchable iodoferrocene derivatives serve as potent catalysts for XB-mediated Friedel-Crafts alkylation reactions, even in competitive polar solvents-a challenging environment for traditional XB catalysis. This work demonstrates the efficacy of charge modulation by redox activation in fine-tuning XB strength for organic transformation.