The Lewis acidity of trialkoxyboranes: a reinvestigation

Abstract

A reinvestigation into the Lewis acidity of trialkoxyboranes B(OR)₃, has shown that contrary to earlier reports none of these compounds forms Lewis acid–base adducts with nitrogen bases. However they do form ‘onium’ salts in which the anion is a tetra-alkoxyborate complex. The thermodynamic stability of these salts is discussed and is shown to be critically dependent upon the crystal lattice energy and temperature. Triphenoxyborane forms the piperidine adduct and corresponding piperidinium salt.