Oxygen-bridged borate anions from tris(pentafluorophenyl)borane: Synthesis, NMR characterization, and reactivity
Oxygen-bridged borate anions from tris(pentafluorophenyl)borane: Synthesis, NMR characterization, and reactivity
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DOI：
10.1021/ic0502168
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发表时间：
2005-07-11
影响因子：
4.6
通讯作者：
Sironi, A
中科院分区：
文献类型：
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作者：
Di Saverio, A;Focante, F;Sironi, A
先前已知的阴离子[（C6 F5）（3）B（mu-OH）B（C6 F5）（3）]（-）（2）已通过两步程序制备，包括使（C6 F5）（3）BOH 2去质子化以得到[B（C6 F5）（3）OH]（-）（1），随后加入B（C6 F5）（3）。用H-1和F-19核磁共振谱研究了2的溶液结构和动力学。[NHEt 3]2与NEt 3的反应导致形成[NHEt 3]（+）[（C6 F5）（3）BOH]（-）、[NHEt 3]（+）（C6 F5）（3）[BH]（-）和（C6 F5）（3）B-（CH 2CH =N+ Et 2）。这表明在亲核阴离子的存在下，2可以解离成B（C6 F5）（3）和1。[HDMAN]2与1，8-二（二甲氨基）萘（DMAN）的反应证实了这一趋势。在水存在下，2生成[（C6 F5）（3）BO（H）（HO）-O-.（H）B（C6 F5）（3）]（-）（3），含有与配位到B（C6 F5）（3）的水分子氢键结合的硼酸酯1。通过用0.5当量的碱处理（C6 F5）（3）BOH 2形成相同的化合物。一项竞争性研究证实，对于1，与B（C6 F5）3的刘易斯酸碱相互作用比与（C6 F5）（3）BOH 2的氢键作用优先约5倍。[2-甲基-3 H-indolium]3的X射线单晶分析提供了在[H3 O2]（-）部分中的不对称氢键的第一个实验观察，测量的O-H和（HO）-O-...键距显著不同[1.14（2）对1.26（2）埃]。NEt 3与B（C6 F5）（3）和双（五氟苯基）硼酸（C2 F5）（5）BOH的等摩尔混合物反应，得到新的硼合硼酸盐[NHEt 3]（+）[（C6 F5）（3）BO B（C6 F5）（2）]（-）（[NHEt 3]4）。X射线衍射分析表明，B-O键长明显短于[（C6 F5）（3）B（μ-OH）B（C6 F5）（3）]（-）。可变温度的F-19 NMR显示高流动性的五个芳基环，在与更拥挤的阴离子2的差异。2D NMR相关实验表明，在CD 2Cl 2中，两个阴离子[（C6 F5）（3）BOH]（-）和[（C6 F5）（3）BH]（-）与[NHEt 3]（+）形成紧密的离子对，其中NH质子建立常规的（（BOHN）-H-.）或非常规（（BHHN）-H-.），分别与阴离子形成氢键。相反，二硼酸根阴离子2-4与铵阳离子形成松散的离子对，这是由于离域的阴离子电荷和应充当H键受体的氧原子的空间位阻位置。
The previously known anion [(C6F5)(3)B(mu-OH)B(C6F5)(3)](-) (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)(3)BOH2 to give [B(C6F5)(3)OH](-) (1), followed by addition of B(C6F5)(3). The solution structure and the dynamics of 2 have been investigated by H-1 and F-19 NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3](+)[(C6F5)(3)BOH](-), [NHEt3](+)(C6F5)(3)[BH](-), and (C6F5)(3)B-(CH2CH=N+Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)(3) and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino) naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)(3)BO(H)(HO)-O-...(H)B(C6F5)(3)](-) (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)(3). The same compound is formed by treating (C6F5)(3)BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)(3)BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2](-) moiety, the measured O-H and (HO)-O-... bond distances being significantly different [1.14(2) vs 1.26(2) angstrom]. The reaction of NEt3 with an equimolar mixture of B(C6F5)(3) and bis(pentafluorophenyl)borinic acid, (C2F5)(5)BOH, afforded the novel borinatoborate salt [NHEt3](+)[(C6F5)(3)BOB(C6F5)(2)](-) ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)(3)B(mu-OH)B(C6F5)(3)](-). Variable-temperature F-19 NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)(3)BOH](-) and [(C6F5)(3)BH](-) form tight ion pairs with [NHEt3](+), in which the NH proton establishes a conventional ((BOHN)-H-...) or an unconventional ((BHHN)-H-...), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.