Spectroscopic and Computational Investigations of The Thermodynamics of Boronate Ester and Diazaborole Self-Assembly

The solution phase self-assembly of boronate esters, diazaboroles, oxathiaboroles, and dithiaboroles from the condensation of arylboronic acids with aromatic diol, diamine, hydroxythiol, and dithiol compounds in chloroform has been investigated by 1H NMR spectroscopy and computational methods. Six arylboronic acids were included in the investigations with each boronic acid varying in the substituent at its 4-position. Both computational and experimental results show that the para-substituent of the arylboronic acid does not significantly influence the favorability of forming a condensation product with a given organic donor. The type of donor, however, greatly influences the favorability of self-assembly. 1H NMR spectroscopy indicates that condensation reactions between arylboronic acids and catechol to give boronate esters are the most favored thermodynamically, followed by diazaborole formation. Computational investigations support this conclusion. Neither oxathiaboroles nor dithiaboroles form spontaneo...