BF2 complex of fluorinated dipyrrolyldiketone: a new class of efficient receptor for acetate anions.

The beta-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 (CH3CO(2-)), associating more effectively than anions such as F-, Cl-, Br-, H2PO(4-), and HSO(4-), is estimated to be 9.6 x 10(5) M(-1), approximately 9 times larger than that of the beta-H derivative 2a (1.1 x 10(5) 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.