Anion complexation by bidentate Lewis acidic hosts, ortho-bis(fluorosilyl) benzenes

Article abstract of DOI:10.1016/0022-328X(95)05636-4

Ortho-bis(fluorosilyl)benzenes, precursors for bis-siliconates, o-C₆H₄(SiPhF₂)₂ (1), o-C₆H₄(SiF₃)(SiPh₂F) (2) and o-C₆H₄(SiPhF₂)(SiPh₂F) (3), possess anion binding properties as bidentate Lewis acidic hosts in organic solvents. Compound 1 quantitatively binds a fluoride ion from KF suspended in acetone or tetrahydrofuran without support of 18-crown-6 to form the corresponding soluble bis-siliconate [o-C₆H₄(SiPhF₂)₂F]K (4). The binding constants of a series of fluorosilanes for a fluoride ion are measured by ¹H and ¹⁹F NMR spectroscopies. The affinity of fluorosilanes towards a fluoride ion increases in the order PhMeSiF² (7) < Ph₂SiF₂ (9) < 3 < 1 < 2. The fluoride ion binding constant of 2 is estimated to be K > 1.1 × 10⁹ M^-1 at 193 K. These bidentate Lewis acids 1-3 are among the strongest organic hosts for a fluoride ion in organic solvents ever reported.