Synthesis and study of monomeric and dimeric boronates by spectroscopic methods and X-ray crystallography

A series of 2-salicylideneamino ethanol derivatives with substituents in different positions have been brought to reaction with phenylboronic acid. Depending on the number and position of the substituents in the ligand, three boronate structure types have been obtained. Thereby, it could be shown that the formation of a macrocyclic dimeric boronate is preferred over the monomeric compound and a [5.4.0]heterobicyclic system with a B(4)-O-B(3) structural unit. The three structure types have been analyzed by X-ray crystallography, where a series of parameters such as N-->B bond length, torsion angles, tetrahedral character at the boron atom, deviation of the boron atom from the mean plane and sum of bond angles in the heterocyclic rings have been evaluated in order to determine the factors for the preferred formation of each compound. Finally a new synthetic strategy is presented that permits the synthesis of other macrocyclic boronates in the future.