Synthesis of the Soft Lewis Superacid Tris(4-bromo-2,3,5,6-tetrafluorophenyl)borane B(C6F4Br)3 via C‒Ag to C‒B Transmetalation

Abstract

The Lewis acid tris(4-bromo-2,3,5,6-tetrafluorophenyl)borane B(C6F4Br)3 was synthesized via transmetalation from BBr3 and AgC6F4Br. The latter was prepared from 1,4-C6F4BrSiMe3 with AgF and crystallized as a toluene solvate [2(AgC6F4Br)4•7.46(toluene)]. The solid-state structure of free B(C6F4Br)3 and its Lewis base adducts with EtCN, H2O, and POEt3 was determined by single-crystal X-ray diffraction. DFT calculations show that B(C6F4Br)3 has approximately 1% higher fluoride and hydride ion affinities (FIA and HIA) than tris(pentafluorophenyl)borane B(C6F5)3. Similarly, the Gutmann-Beckett method indicates an increase in Lewis acidity of 2%, whereas IR spectroscopy of the CD3CN adducts reveals a slightly lower ṽ(CN) vibration for B(C6F4Br)3. The presence of bromine atoms is expected to facilitate structural analysis of Lewis acid-base adducts of B(C6F4Br)3 by single-crystal X-ray diffraction in the future.