Polyfluorinated versus cationic multidentate halogen-bond donors: A direct comparison

• Synthesis of polyfluorinated multidentate halogen-bond donors with azo linkage
• Geometry of iodine centres almost identical to pyridinium-based halogen-bond donors
• Much weaker activation of test substrate compared to cationic variants
• Comparison of Lewis acidity by DFT calculations supports experiments

Two polyfluorinated azo-linked halogen-bond donors were synthesized and their relative Lewis acidities were compared to a known dicationic azo-linked halogen-bond donor with almost identical geometrical arrangement of the iodine substituents. This structural similarity was confirmed by the results of x-ray structural analyses. In a benchmark reaction to gauge the activation potential of these halogen-based Lewis acids in halide abstraction reactions, we found that the polyfluorinated compounds were markedly less active than the cationic ones and did, in fact, show very little activation at all. Repeated measurements seem to indicate however, that there is a small effect of the iodinated versus the non-iodinated polyfluorinated compound in their role as potential activators. Quantum-chemical calculations confirmed the experimentally observed trend.

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