Just at the limit: binding studies with neutral brominated terphenyl-derived halogen bond donors

Bromine-based halogen bond donors should constitute markedly weaker Lewis acids compared to their iodinated counterparts, yet the actual difference has rarely been quantified. Here, we report investigations of the binding strength and recognition potential of such neutral halogen bond donors. As expected, a considerable decrease in binding affinity was observed in NMR titrations and single crystal analyses. Adducts of the donors with iodide salts showed only weak interactions in the solid state. Accompanying NMR titrations of the donors with different halide salts in tetrahydrofuran yielded binding constants three orders of magnitude lower than those of their iodinated analogues. Additionally, the potential three-point binding of phenyl-substituted-terphenyl-based donors towards a suitably chosen orthoamide was lowered by two orders of magnitude. A systematic comparison of brominated neutral halogen bond donors against their iodinated analogues in the gas phase, solid state, and in solution.