Novel hydrogen bond observed between a carborane B–H and a phenyl ring

A weak type of hydrogen bond is known to form between C–H, N–H, and O–H groups and the π electron cloud of an aromatic ring. Similar interactions have been predicted for B–H groups on compounds such as diborane (B₂H₆) and o-carborane (C₂B₁₀H₁₂), in which the electronic structure produces a slight positive charge on the B–H hydrogens. A complex with a B–H···π interaction has now been created and characterized by a team led by Hong Yan of Nanjing University and Dieter Cremer of Southern Methodist University (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b01249). The ability to promote such interactions could have applications in molecular assembly and pharmaceutical binding. The researchers treated an iridium-dithiolene-carborane complex with phosphines to produce a molecule in which a carborane B–H group is in position to form a hydrogen bond with one of the phosphine phenyl rings. The researchers confirmed the hydrogen bond experimentally using NMR and X-ray crystallography studies, finding a H···π distance of 240 to 276 pm. Computational analysis of the local stretching force constant of the hydrogen bond reveals that the strength of the B–H···π interaction is similar to that of the hydrogen bond in a water dimer.