Cyanide ion complexation by a cationic borane
Cyanide ion complexation by a cationic borane
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DOI：
10.1039/b715534d
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发表时间：
2008-01-01
影响因子：
4
通讯作者：
Gabbaie, Francois P.
中科院分区：
文献类型：
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作者：
Chiu, Ching-Wen;Gabbaie, Francois P.
虽然我们以前报道过[1-(Mes(2)B)-8-(Me3NCH2)- c10h6](+)（[2](+)）配合氟离子形成[1-(Mes(2)FB)-8-(Me3NCH2)- c10h6](2- f)，但我们现在表明，这种阳离子硼烷也配合氰化物形成[1-(Mes(2)(NC)B)-8-(Me3NCH2)- c10h6]（2- cn）。该反应也发生在双相条件下（H2O-CHCl3），并可能在有机相中运输氰化物。对两性离子氰硼酸盐2-CN进行了全面表征，并确定了其晶体结构。在THF中进行的紫外-可见滴定实验表明，[2]（+）对氟化物（K > 10(8) M-1）的亲和力高于氰化物（K = 8.0 （+/- 0.5） × 10(5) M-1）。阻碍氰化物与[2]（+）的空间拥挤的硼中心结合的空间效应最有可能是这种选择性的起源。最后，电化学研究表明，[2]（+）的亲电性明显优于其中性前体1-(Mes(2)B)-8-(Me2NCH2)-(C10H6)(1)。这些研究还表明，[2]（+）的还原是不可逆的，可能是由于还原条件下NMe3部分的消除。实际上，[2]OTf与NaBH4反应生成1-(Mes(2)B)-8-(CH3)-(C10H6)(4)，该产物也已被充分表征。
While we have previously reported that [1-(Mes(2)B)-8-(Me3NCH2)-C10H6](+) ([2](+)) complexes fluoride ions to form [1-(Mes(2)FB)-8-(Me3NCH2)-C10H6](2-F), we now show that this cationic borane also complexes cyanide to form [1-(Mes(2)(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-(Mes(2)B)-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-(Mes(2)B)-8-(CH3)-(C10H6) (4) which has also been fully characterized.