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.
Hudnall
Todd W
TW
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
Kim
Young-Min
YM
Bebbington
Magnus W P
MW
Bourissou
Didier
D
Gabbaï
François P
FP
D000143:Acids / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005459:Fluorides / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000737:chemistry*
D000143:Acids; D001880:Boranes; D002614:Chelating Agents; D007477:Ions; D009943:Organophosphorus Compounds; D005459:Fluorides