Structural and electrochemical investigations of the high fluoride affinity of sterically hindered 1,8-bis(boryl)naphthalenes.
Structural and electrochemical investigations of the high fluoride affinity of sterically hindered 1,8-bis(boryl)naphthalenes.
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DOI：
10.1021/ic060709s
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发表时间：
2006-08
影响因子：
4.6
通讯作者：
Mohand Melaïmi;S. Solé;Ching‐Wen Chiu;Huadong Wang;F. Gabbaï
中科院分区：
文献类型：
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作者：
Mohand Melaïmi;S. Solé;Ching‐Wen Chiu;Huadong Wang;F. Gabbaï
10-溴-9-氧杂-10-硼蒽与二亚甲基-1,8-萘二基硼酸的四(四氢呋喃)锂盐在乙醚中反应，得到1-(二亚甲基硼基)-8-(10'-硼-9'-氧杂蒽基)萘(2)。该乙硼烷与 [Me3SiF2][S(NMe2)3)] 反应，得到阴离子络合物 [2-mu2-F]-，该络合物已以 [S(NMe2)3]+ 盐形式分离出来。乙硼烷 2 以及 1-(二甲基硼基)-8-(10'-bora-9'-硫杂蒽基)萘 (1) 的循环伏安图在 E(1/2) = -2.200 和 -2.566 V（相对于 FcH/FcH+）处表现出两个可逆还原，1 和 E(1/2) = -2.248 和2 的 -2.620 V（相对于 FcH/FcH+）对应于两个硼中心的顺序还原。添加氟化物后，这两个波同时消失，从而表明形成了氟化物螯合物[1-mu2-F]-和[2-mu2-F]-。为了确定这些乙硼烷表现出的高氟化物亲和力的来源，对 2 和 [2-mu2-F]- 的结构进行了实验和计算研究。晶体学研究表明2的结构是扭曲的，从而表明相邻硼基部分之间存在重要的空间排斥。相比之下，阴离子配合物 [2-mu2-F]- 的结构比 2 的结构更加空间松弛，如 B-B 距离从 2 中的 3.279(4) A 减少到 [2-mu2-F]- 中的 2.922(7) A 所示。结构结果表明，2 结果显示出高氟化物亲和力，至少部分是由于氟化物结合引起的空间排斥的缓解。最后，使用密度泛函理论计算和分子内原子分析研究了 [2-mu2-F]- 的 B-F-B 桥中的键合性质以及相互作用的强度。这些计算表明，与 [2-mu2-F]- 中两个 B-F 键形成相关的焓增益仅相当于末端 B-F 键能量的一小部分。这些计算还表明，2 中氟化物结合引起的空间排斥的缓解可能有助于这些类型分子的高氟化物亲和力。
The reaction of 10-bromo-9-oxa-10-boraanthracene with the tetrakis(tetrahydrofuran)lithium salt of dimesityl-1,8-naphthalenediylborate in diethyl ether affords 1-(dimesitylboryl)-8-(10'-bora-9'-oxaanthryl)naphthalene (2). This diborane reacts with [Me3SiF2][S(NMe2)3)] to afford the anionic complex [2-mu2-F]-, which has been isolated as a [S(NMe2)3]+ salt. The cyclic voltammograms of diborane 2 as well as 1-(dimesitylboryl)-8-(10'-bora-9'-thiaanthryl)naphthalene (1) exhibit two reversible reductions at E(1/2) = -2.200 and -2.566 V (vs FcH/FcH+) for 1 and E(1/2) = -2.248 and -2.620 V (vs FcH/FcH+) for 2 corresponding to the sequential reduction of the two boron centers. These two waves simultaneously disappear upon fluoride addition, thus indicating the formation of fluoride chelate complexes [1-mu2-F]- and [2-mu2-F]-. To identify the origin of the high fluoride affinity displayed by these diboranes, the structures of 2 and [2-mu2-F]- have been studied experimentally and computationally. The crystallographic studies show that the structure of 2 is distorted, thus indicating the presence of important steric repulsions between the neighboring boryl moieties. By contrast, the structure of the anionic complex [2-mu2-F]- is much more sterically relaxed than that of 2, as indicated by a reduction of the B-B distance from 3.279(4) A in 2 to 2.922(7) A in [2-mu2-F]-. The structural results suggest that the high fluoride affinity displayed by 2 results, at least in part, from the relief of steric repulsions induced by fluoride binding. Finally, the nature of the bonding as well as the strength of the interactions involved in the B-F-B bridge of [2-mu2-F]- has been studied using density functional theory calculations and Atoms-In-Molecules analyses. These calculations indicate that the enthalpic gain associated with the formation of two B-F bonds in [2-mu2-F]- only amounts to a fraction of the energy of a terminal B-F bond. These calculations also suggest that the relief of steric repulsions induced by fluoride binding in 2 may contribute to the high fluoride affinity of these types of molecules.