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 center dot 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 (K-a) of 2b for acetate(CH3CO2-), associating more effectively than anions such as F-, Cl-, Br-, H2PO4-, and HSO4-, is estimated to be 9.6 x 10(5) M-1, similar to 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.