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Dalton Transactions

The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2008, 814 - 817, DOI: 10.1039/b715534d

Cyanide ion complexation by a cationic borane

Ching-Wen Chiu and François P. Gabbaï

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.

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