X-ray crystallographic study of three (N→B)-borinates prepared from 8-hydroxyquinoline and 2-hydroxypyridine

8-Hydroxyquinoline and 2-hydroxypyridine have been reacted with diphenylborinic acid or 9-BBN; the molecular structure of the resulting heterocycles has been studied by X-ray crystallography. A structural comparison of the so formed five- and six-membered heterocycles with similar complexes obtained from aliphatic amino alcohol and α-amino acid derivatives shows significant differences for the N→B, B−O and B−C bond lengths and some of the inner cycle bond angles. Other structural parameters discussed in this respect are the sum of bond lengths at the boron atom, the sum of bond angles in the heterocycle and the tetrahedral character of the boron atom. On the basis of these parameters a qualitative comparison of heterocycle stability is possible.