Fluoride ion chelation by a bidentate phosphonium/borane Lewis acid.


The phosphonium borane [1-Mes2B-2-MePh2P-(C6H4)]+ ([2]+) has been synthesized as an iodide salt by alkylation of 1-Mes2B-2-Ph2P-(C6H4) with MeI. This novel cationic borane complexes fluoride to afford the corresponding zwitterionic fluoroborate complex 1-FMes2B-2-MePh2P-(C6H4) (2-F) with a binding constant in MeOH exceeding that of 1-Mes2B-4-MePh2P-(C6H4) ([1]+) by at least 4 orders of magnitude. Structural and computational results indicate that the high fluorophilicity of [2]+ arises from both Coulombic and cooperative effects which lead to formation of a B-F-->P interaction with a F-->P distance of 2.666(2) A. These results, which are supported by NBO and AIM analyses, show that the latent phosphorus-centered Lewis acidity of the phosphonium moiety in [2]+ can be exploited to enhance fluoride binding via chelation.

DOI: 10.1021/ja804492y

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@article{Hudnall2008FluorideIC, title={Fluoride ion chelation by a bidentate phosphonium/borane Lewis acid.}, author={Todd W Hudnall and Young-Min Kim and Magnus W P Bebbington and Didier Bourissou and François P Gabba{\"{i}}, journal={Journal of the American Chemical Society}, year={2008}, volume={130 33}, pages={10890-1} }