A computational study of the formation of 1,3,2-dioxaborolane from the reaction of dihydroxy borane with 1,2-ethanediol

Abstract

Boronic acids are well known to form covalent linkages with compounds containing 1,2- or 1,3-diol moieties that lead to 5- or 6-membered cyclic boronate esters, respectively. In the present study, we use density functional theory at the B3LYP/6-311++G** computational level to discuss formation of the representative 5-membered cyclic ester 1,3,2-dioxaborolane, HB(–O–CH 2–CH 2–O–), from the dehydration reaction of dihydroxy borane, HB(OH) 2, and 1,2-ethanediol, HOCH 2–CH 2OH. Calculations support a stepwise mechanism in which the monoester HB(OH)–O–CH 2–CH 2OH is formed in an initial bimolecular dehydration; this is followed by a unimolecular elimination in which HB(–O–CH 2–CH 2–O–) is formed. Since diol complexations with boronic acids are typically carried out either in aprotic solvents using a dehydrating agent or in basic aqueous media, the effects of acetonitrile and various Lewis bases on the thermodynamic and kinetic parameters of these dehydration and elimination reactions are also discussed.