Structures and properties of trifluoromethylphenylboronic acids

Abstract

Three isomers of trifluoromethylphenylboronic acids were synthesized and characterized by 1H, 13C, 11B and 19F NMR. The investigated compounds exhibit high resistance to protodeboronation reaction. Molecular and crystal structure of these compounds was determined by single crystal XRD method. The compounds form typical hydrogen-bonded dimers with the syn-anti conformation. CF3 substituent does not interact with boronic moiety neither as hydrogen bond acceptor nor a lone-electron pair donor. pKa values of the isomers have been determined by spectrophotometric and potentiometric method. Introduction of the CF3 group increases the acidity for meta and para isomers in comparison to the phenylboronic acid, while for the ortho isomer the acidity is reduced due to the steric hindrance.