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 diphenylbor inic acid or 9-BBN; the molecular structure of the resulting heterocycles h as 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 a-amino acid derivatives shows significan t differences for the N-B, B-O and B-C bond lengths and some of the inner c ycle 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 h eterocycle and the tetrahedral character of the boron atom. On the basis of these parameters a qualitative comparison of heterocycle stability is poss ible.