In the past year, a large part of our efforts has been dedicated to the chemistry of organoboranes whose ligands are decorated by cationic groups.  The presence of these cationic groups increases the electrophilic characters of these main group compounds as reflected by their unusual coordination and reduction chemistry. 

      We have been able to synthesize the a-borylated cation [1]⁺ which, as indicated by cyclic voltammetry, can be reduced by one and two electron to produce the neutral radical 1^• and the borataalkene [1]^-.  Structural characterization of [1]⁺, 1^• and [1]^- indicates the stepwise population of the boron-carbon p-bonding orbital upon reduction.  In particular, the central B-C bond determined for 1 (1.559(5) Å) lies almost exactly between the B-C single bond measured in [1]⁺ (1.627(5) Å) and the B=C double bond measured in [1]^- (1.462(8) Å).  Natural Bond Order analysis of [1]⁺, 1^• and [1]^- confirms that reduction of [1]⁺ results in the sequential population of the central boron-carbon p bond of this derivative.  Some of the important outcomes of this work include: 1) the discovery and structural characterization of a new stable radical (1^•) in which the unpaired electron is partly localized in a boron-carbon p-bond; 2) the discovery that borataalkenes are amenable to reversible redox chemistry and can in fact be considered as the reduced form of a-borylated carbocations.

      Another major thrust of our recent research concerns the design of cationic boranes for the complexation of fluoride and cyanide ions in aqueous media.  After investigating the anion binding affinity of neutral bidentate boranes, we have now discovered that simple cationic boranes are competent for the complexation of fluoride ions in the presence of water.  Cationic borane [2]⁺ is first cationic borane that we were able to prepare.  Unlike neutral borane, [2]⁺ captures fluoride ions from water under biphasic conditions (H₂O/CHCl₃) to form 2-F.  Interestingly, however, [2]⁺ failed to capture fluoride in aqueous solutions.  Stimulated by this limitation, we decided to explore ammonium and phosphonium boranes [3]⁺, [4]⁺ and [5]⁺ in which the cationic group and the boron center are connected by a phenylene unit.  Studies of the anion binding properties of these derivatives showed that both [3]⁺ and [5]⁺ capture fluoride in aqueous solutions with binding constant in the 600-1000 M^-1 range.  Another interesting outcome of this studies is the fact that [4]⁺ is a selective receptor for cyanide in aqueous solutions.  Altogether, these surprising results indicate that the Lewis acidity of these receptors can be substantially increased by the presence of a cationic moiety.  Finally, we have also confirmed that these favorable effects can be used to increase the fluoride binding constants of bidentate borane such as the heteronuclear B/Hg derivative [6]⁺.