Synthesis and Anion Binding Properties of Multi-phosphonium Triarylboranes: Selective Sensing of Cyanide Ions in Buffered Water at pH 7

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• 作者：Ki Cheol Song ; Kang Mun Lee ; Nguyen Van Nghia ; Woo Young Sung ; Youngkyu Do ; Min Hyung Lee
• 刊名：Organometallics
• 出版年：2013
• 出版时间：February 11, 2013
• 年：2013
• 卷：32
• 期：3
• 页码：817-823
• 全文大小：384K
• 年卷期：v.32,no.3(February 11, 2013)
• ISSN：1520-6041

文摘

A series of mono-, di-, and triphosphonium-substituted triarylboranes, [Mes₂BAr^P]I ([2]I), [MesBAr^P₂]I₂ ([3]I₂), and [BAr^P₃]I₃ ([4]I₃) (Ar^P = 4-(MePh₂P)-2,6-Me₂-C₆H₂), were prepared from the corresponding neutral boranes 2a鈥?b>4a. The crystal structure of [4]I₃ determined by X-ray diffraction study reveals peripheral decoration of aryl groups with phosphonium moieties. The anion affinity of the cationic boranes for fluoride and cyanide ions was investigated by UV鈥搗is absorption titrations in aqueous solution. The triarylboranes, [2]I鈥揫4]I₃ bind both fluoride and cyanide ions in a DMSO/H₂O (7:3 v/v) mixture with high binding constants (K). Comparison of the K values of triarylboranes for fluoride reveals that fluorophilicity increases with the increasing number of phosphonium moieties: [2]⁺ (K = 2.3 脳 10¹ M^鈥?) < [3]²⁺ (3.6 脳 10⁵ M^鈥?) < [4]³⁺ (1.0 脳 10⁷ M^鈥?). A similar trend is also observed in the cyanide binding, with K values that are greater by 2鈥? orders of magnitude than those in the fluoride binding. These results indicate an apparent additive effect of multiple phosphonium substitutions on the Lewis acidity enhancement of triarylboranes. The triphosphonium borane [4]Cl₃, a water-soluble form of [4]I₃, was further utilized in evaluating the anion affinity in water. While [4]³⁺ is shown to hardly bind fluoride in buffered water at pH 7, it binds cyanide with a high binding constant (1.7 脳 10⁷ M^鈥?).