A sandwich complex of trimesitylborane Mes(3)B: synthesis, characterization and anion binding properties of Mes(2)B[(eta(6)-Mes)FeCp](+)
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abstract
As part of our continuing interest in the chemistry of Lewis acidic organoboron compounds as anion receptors, we have synthesized the hexafluorophosphate salt of the cationic borane Mes2B[( 6-Mes)FeCp]+ ([1]+) by reaction of [(6-naphthalene)FeCp][PF6] with Mes3B. This compound, which undergoes two quasi-reversible reductions at E 1/2 = -1.56 V and -2.40 V, reacts with both fluoride and cyanide anions in THF or MeOH to afford the corresponding zwitterionic fluoro- (1-F) and cyano-borate (1-CN) species, respectively. Spectrophotometric titrations carried out in THF indicate that the fluoride and cyanide binding constants of [1]+ are much larger than those of Mes3B. This difference points to the favorable inductive and coulombic effects imparted by the cationic [CpFe]+ moiety on the Lewis acidity of the boron center. 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
