Crystalline Water Adducts of a Dual-Site Lewis Superacidic Borane

In this contribution, we present the reactions of two different three-dimensional analogues of 9,10-diyhdro-9,10-diboraanthracene (3D-DBAs), which act as dual-site Lewis superacids, with water. While 3D-DBA^Cl (Cl on boron) readily reacts with water to yield the first hydroxy-functionalized 3D-DBA (3D-DBA^OH), the phenyl derivative 3D-DBA^Ph forms a water adduct, 3D-DBA^Ph·(H₂O)₂, which is stable in THF and H₂O and has been single crystal structurally characterized. All new compounds have been analyzed by NMR spectroscopy, single crystal X-ray diffraction analysis and elemental analysis. Quantum chemical calculations demonstrate the considerably high water affinity of 3D-DBA^Ph and the Brønsted superacidity of 3D-DBA^OH and 3D-DBA^Ph·(H₂O)₂.