Dihydrogen Bond in the Aminoborane Complex of a Nicergoline Intermediate.

An aminoborane side product from the nicergoline manufacture process was identified by single-crystal X-ray diffraction. As boranes of pharmaceutical molecules are quite rare, the binding potential of the BH group was investigated and compared with similar compounds using Cambridge Structural Database (CSD). Surprisingly, the packing was stabilized by a dihydrogen bond, which triggered a false alert for too-short contact of hydrogen atoms in IUCR checkCIF. As the dihydrogen bond concept is not widely known, such an alert might mislead crystallographers to force -CH optimal geometry to -BH groups. The B-H distances equal to or less than 1.0 Å (17% of the CSD structures) are substantially biased when analyzing the structures of aminoborane complexes in CSD. To conduct proper searching, B-H bond length normalization should be applied in the CSD search.