Boron–Nitrogen Double Tweezers Comprising Arylboronic Esters and Diamines: Self‐Assembly in Solution and Adaptability as Hosts for Aromatic Guests in the Solid State

The thermodynamic stability of 1 : 1 and 2 : 1 boron–nitrogen (B←N) adducts formed between aromatic boronic esters with mono‐ and diamines was studied in solution by NMR and UV‐vis spectroscopy with association energies (ΔG°) ranging from −11 to −28 kJ mol−1. The effect of different substituents in the boronic ester, the nature of the diamine linker, and the effect of the solvent was explored. Stable 2 : 1 B←N adducts with diamines such as 1,3‐diaminopropane were produced in solutions of hydrogen‐bonding acceptor solvents (acetonitrile and ethyl acetate), which can be isolated in the solid state as crystalline solvates, whereas the use of noncoordinating solvents such as 1,2‐dichloroethane afforded mainly 1 : 1 B←N adducts. In suitable combinations, aromatic bis‐pyridyl diamines produced stable 2 : 1 B←N adducts that were isolated either as solvent‐free solids, solvates, or cocrystals. In these crystalline forms, double‐tweezer hosts were observed with an exceptional syn/anti conformational guest‐adaptability driven by simultaneous donor‐acceptor and C−H⋅⋅⋅π interactions in the tweezer cavities, resembling preorganized covalent tweezer hosts. Interestingly, cocrystals with electron‐rich guests such as tetrathiafulvalene and pyrene showed non‐centrosymmetric crystal lattices with infinite π‐stacked donor–acceptor columns. Great hosts: Studies of the thermodynamic stability of Lewis‐type boron–nitrogen (B←N) adducts between aromatic boronic esters and aliphatic/aromatic mono‐ and diamines in different solvents provided insights into the factors enabling the generation of stable 2 : 1 adducts in solution. Crystalline solids of these adducts with diamine linkers exhibited syn/anti double‐tweezer conformations depending on the guest included, and formed cocrystals with infinite π‐stacked columns.