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Issue 6, 2008
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Cyanide ion complexation by a cationic borane

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While we have previously reported that [1-(Mes2B)-8-(Me3NCH2)-C10H6]+ ([2]+) complexes fluoride ions to form [1-(Mes2FB)-8-(Me3NCH2)-C10H6] (2-F), we now show that this cationic borane also complexes cyanide to form [1-(Mes2(NC)B)-8-(Me3NCH2)-C10H6] (2-CN). This reaction also occurs under biphasic conditions (H2O–CHCl3) and may serve to transport cyanide in organic phases. The zwitterionic cyanoborate 2-CN has been fully characterized and its crystal structure determined. UV-vis titration experiments carried out in THF indicate that [2]+ has a higher affinity for fluoride (K > 108 M−1) than cyanide (K = 8.0 (±0.5) × 105 M−1). Steric effects which impede cyanide binding to the sterically congested boron center of [2]+ are most likely at the origin of this selectivity. Finally, electrochemical studies indicate that [2]+ is significantly more electrophilic than its neutral precursor 1-(Mes2B)-8-(Me2NCH2)-(C10H6) (1). These studies also show that reduction of [2]+ is irreversible, possibly because of elimination of the NMe3 moiety under reductive conditions. In fact, [2]OTf reacts with NaBH4 to afford 1-(Mes2B)-8-(CH3)-(C10H6) (4) which has also been fully characterized.

Graphical abstract: Cyanide ion complexation by a cationic borane

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The article was received on 09 Oct 2007, accepted on 08 Nov 2007 and first published on 04 Dec 2007

Article type: Paper
DOI: 10.1039/B715534D
Dalton Trans., 2008, 814-817

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    Cyanide ion complexation by a cationic borane

    C. Chiu and F. P. Gabbaï, Dalton Trans., 2008, 814
    DOI: 10.1039/B715534D

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