Complementary anion binding by bidentate boron-containing Lewis acids

Abstract

Anion binding by the pyroborates (catB) 2O ( 1, cat = O 2C 6H 4-1,2) and ( S, S-Ph 2C 2H 2O 2B) 2O ( 2) has been investigated by spectroscopic, structural and titration methods. 1 has been shown to act as a bifunctional Lewis acid, exemplified by the complementary (1:1) binding of bidentate bases such as acetate and dihydrogen phosphate. The former complex has been characterized in the solid state by X-ray diffraction and a binding constant of 1500 ± 550 M −1 determined in chloroform solution. The reaction of 2 with acetate, by contrast, leads to breakdown of the Lewis acid chelate and to the formation of the homochiral borate anion [( S, S-Ph 2C 2H 2O 2) 2B] − in good yield (84% based on the chiral component).