BF₂ Complex of Fluorinated Dipyrrolyldiketone: A New Class of Efficient Receptor for Acetate Anions

The β-fluorinated derivative (2b) of the 1,3-dipyrrolyl-1,3-propanedione BF2 complex has been prepared from 3,4-difluoropyrrole and malonyl chloride, followed by treatment with BF3·OEt2. Despite the simple, acyclic, and neutral structure, 2b exhibits efficient 1:1 binding for anions in CH2Cl2 using the bridging CH and pyrrole NH as interaction sites. The binding constant (Ka) of 2b for acetate (CH3CO2-), associating more effectively than anions such as F-, Cl-, Br-, H2PO4-, and HSO4-, is estimated to be 9.6 × 105 M-1, ∼9 times larger than that of the β-H derivative 2a (1.1 × 105 M-1). The UV−vis and fluorescence spectral changes of 2b elucidate the effective recognition of an amino acid, such as phenylalanine, in the anionic form; this is also supported by CD spectral changes with mirror images by l- and d-isomers. Furthermore, in the solid state, BF2 complex 2b provides Cl--bridged supramolecular networks and, in sharp contrast, deprotonated “anionic” self-assembled structures by F- binding.