Cyanide ion complexation by a cationic borane.
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 > 10(8) M(-1)) than cyanide (K = 8.0 (+/-0.5) x 10(5) 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.
Chiu
Ching-Wen
CW
Department of Chemistry, Texas A&M University, College Station, Texas, 77843, USA.
Gabbaï
François P
FP
D001880:Boranes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry*; D004563:Electrochemistry; D005459:Fluorides / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet
D001880:Boranes; D003486:Cyanides; D007477:Ions; D009942:Organometallic Compounds; D012997:Solvents; D005459:Fluorides