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

Ortho-bis(fluorosilyl)benzenes, precursors for bis-siliconates, o-C6H4(SiPhF(2))(2) (1), o-C6H4(SiF3)(SiPh(2)F) (2) and o-C6H4(SiPhF(2))(SiPh(2)F) (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(SiPhF(2))(2)F]K (4). The binding constants of a series of fluorosilanes for a fluoride ion are measured by H-1 and F-19 NMR spectroscopies. The affinity of fluorosilanes towards a fluoride ion increases in the order PhMeSiF(2) (7) < Ph(2)SiF(2) (9) < 3 < 1 < 2. The fluoride ion binding constant of 2 is estimated to be K > 1.1 x 10(9) 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.