With the desired bidentate and tridentate coordination corroborated by the solid-state structures, the carborane-derived catalysts were next applied in benchmark reactions that have commonly been used to compare the performance of halogen bond donors of various different types. As a prototypical halide abstraction (anion-binding) reaction, the substitution of 1chloroisochroman with a ketene silyl acetal (Scheme 2) was chosen (see SI ǂ for further details). Yields of the product 5 were determined via 1 H NMR spectroscopy, and even the addition of 20 mol-% of (noniodinated) o-carborane did not induce any reaction (Table , entry 2). In contrast, the same amount of the iodinated monodentate analogue led to a noticeable (but still somewhat low) product formation of 22% after 16 h (entry 3). Even just 5 mol-% of bidentate catalyst m-1 already led to full conversion (entry 4), which was also nearly achieved with 2 mol-% (entry 5), and only the use of 0.5 mol-% lead to a noticeable drop in yield (79%, entry 6). On the other hand, 20 mol-% of the non-iodinated analogue of m-1 did not result in any product (entry 7). These combined observations make evident that the catalytic activity is indeed based on halogen bonding and that bidentate coordination is crucial for high performance. Under identical conditions, catalyst p-1 with its wider bite angle performed worse (entries 8 and 9), which agrees with the titration data of the chloride complexes discussed above and confirms that for smaller substrates, the meta-substituted backbone is superior.