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.