Cooperative Binding in a Phosphine Oxide-Based Halogen Bonded Dimer Drives Supramolecular Oligomerization.

Triphenylphosphine oxide forms halogen-bonded (XB) complexes with pentafluoroiodobenzene and a 1,4-diaryl-5-iodotriazole. The stability of these complexes is assessed computationally and by 31P NMR spectroscopy in toluene-d8 solution, where both complexes are weakly associated. This knowledge is applied to the design and synthesis of two self-complementary phosphine oxide-iodotriazole hybrids that incorporate a phosphine oxide XB acceptor and a 1,4-diphenyl-5-iodotriazole XB donor within the same molecule. The self-complementary design of these modules facilitates their assembly in both toluene-d8 and, surprisingly, DCM-d2 into dimers, with significant stabilities, through the formation of halogen-bonded diads. The stability of these assemblies is a result of significant levels of cooperative binding that is present in both solvents. The connection of two of these hybrid units together, using a flexible spacer, facilitates the aggregation of these modules in DCM-d2 solution, through halogen bonding, forming oligomeric assemblies.