Distiboranes based on ortho-phenylene backbones as bidentate Lewis acids for fluoride anion chelation

Abstract

As part of our efforts in the chemistry of main group platforms that support anion sensing and transport, we are now reporting the synthesis of anitmony-based bidentate Lewis acids featuring the o-C₆F₄ backbone. These compounds can be easily accessed by reaction of the newly synthesized o-C₆F₄(SbPh₂)₂ (5) with o-chloranil or octafluorophenanthra-9,10-quinone, affording the corresponding distiboranes 6 and 7 of general formula o-C₆F₄(SbPh₂(diolate))₂ with diolate = tetrachlorocatecholate for 6 and octafluorophenanthrene-9,10-diolate for 7, respectively. While 6 is very poorly soluble, its octafluorophenanthrene-9,10-diolate analog 7 readily dissolves in CH₂Cl₂ and undergoes swift conversion into the corresponding fluoride chelate complex [7-μ₂-F]⁻ which has been isolated as a [ⁿBu₄N]⁺ salt. The o-C₆H₄ analog of 7, referred to as 8, has also been prepared. Although less Lewis acidic than 7, 8 also forms a very stable fluoride chelate complex ([8-μ₂-F]⁻). Altogether, our experiental results, coupled with computational analyses and fluoride anion affinity calculations, show that 7 and 8 are some of the strongest antimony-based fluoride anion chelators prepared to date. Another notable aspect of this work concerns the use of the octafluorophenanthrene-9,10-diolate ligand and its ablity to impart advantageous solubility and Lewis acidity properties.