Synthesis and reactivity of a 1,8-bis(methylium)naphthalenediyl dication.
Synthesis and reactivity of a 1,8-bis(methylium)naphthalenediyl dication.
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1,8-双(甲基)萘二基二甲基的合成和反应性。
DOI：
10.1002/anie.200353011
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发表时间：
2004
影响因子：
--
通讯作者：
F. Gabbaï
中科院分区：
文献类型：
--
作者：
Huadong Wang;F. Gabbaï
三芳基甲基阳离子构成了一类研究得最好的稳定碳阳离子。[1，2]除了用作染料外，[3]这类物质在烯烃聚合催化领域中已经变得普遍存在，其中它们用作活化剂。[4]这些化合物化学的最新进展集中在它们在双官能衍生物中的掺入。其中，[5]已经制备了一系列双阳离子系统，其中两个三芳基甲基阳离子通过联苯（如A2+）或联萘骨架连接，并显示出独特的电致变色性能。[6，7]结构研究表明，这些联苯或联萘基系统的甲基中心仅相隔3.5 - 3.7。由于固有的库仑排斥，可以假设，甲基中心之间的物理分离控制着这些衍生物的稳定性和反应性。因此，对这种分离的控制可以用于微调这种双官能分子的亲电和刘易斯酸性。应用这种模式的高度亲电和刘易斯酸性双齿分子的合成，我们现在的目标是双（甲基）双阳离子，功能短阳离子间的分离。本文报道了1，8-双（双（对甲氧基苯基）甲基）萘二基二价阳离子（22+）的合成、表征和反应性，该阳离子具有两个甲基中心，中心间距为3.076（2）。1，8-二硫代萘·TMEDA [8]与2摩尔当量的4，4-二甲氧基二苯甲酮反应得到相应的二醇，即1，8-双[双（对甲氧基苯基）羟甲基]萘（1）（方案1）。在用aq [HBF4]和（CF3CO）2O的混合物处理后，该二醇经历双重脱羟基反应，得到相应的二价阳离子22+（方案1）。22+的1H NMR谱表征了对称的近取代萘衍生物的预期信号：2-和7-位氢原子的信号相对于1的类似信号向低场移动1.05 ppm。四个不同的信号的外观连接到对甲氧基苯基基团的芳香族核心的氢表示后者的限制旋转。碳阳离子中心的13 C共振出现在δ = 191.8 ppm处，这与对其他碳阳离子如双（4-甲氧基苯基）苯甲基铁所观察到的相当。[9]单晶X射线分析[10]揭示了空间拥挤结构的存在（图1，顶部）。22+结构中存在的严格几何约束引起萘二基骨架的扭曲。特别值得注意的是C9-C8-C02和C9-C1-C01角（分别为125.36（16）和126.60（15）θ），其大于理想值120 θ。如C01（α（C01-C）= 359.6）和C02（α（C02-C）= 359.8）处的键角之和所示，每个甲基中心采用三角平面排列。C01和C02中心的三角形配位平面与含有萘骨架的平面形成相对大的二面角（分别为59.7和59.68），表明甲基中心空pz轨道与萘骨架的π-系统的共轭只能是适度的。相比之下，对甲氧基苯基强烈地稳定甲基中心，如由它们与C01和C02中心的三方配位平面形成的小二面角所指示的（18.1 - 28.58）。这种内消旋稳定化也通过短的C01-C11、C01-C21、C02-C31和C02-C41键反映。最后，由于这种独特的分子结构，邻位…
Triarylmethylium cations constitute one of the best studied classes of stable carbocations.[1, 2] In addition to being used as dyes,[3] such species have become ubiquitous in the domain of olefin polymerization catalysis where they serve as activators.[4] Recent advances in the chemistry of these compounds focus on their incorporation in bifunctional derivatives. Among these,[5] a series of dicationic systems in which two triarylmethylium cations are linked by a biphenyl (as in A2+) or a binaphthyl backbone have been prepared and have been shown to display unique electrochromic properties.[6, 7] Structural studies indicate that the methylium centers of these biphenyl-or binaphthylbased systems are separated by only 3.5–3.7. Owing to inherent coulombic repulsions, it can be assumed that the physical separation between the methylium centers governs the stability and reactivity of such derivatives. Hence, control over this separation could serve to fine-tune the electrophilic and Lewis acidic properties of such bifunctional molecules. Applying this paradigm to the synthesis of highly electrophilic and Lewis acidic bidentate molecules, we are now targeting bis (methylium) dications that feature short intercationic separation. Herein, we report on the synthesis, characterization, and reactivity of 1, 8-bis (bis (p-methoxyphenyl) methylium) naphthalenediyl dication (22+), which features two methylium centers separated by 3.076 (2). The reaction of 1, 8-dilithionaphthalene· TMEDA [8] with two molar equivalents of 4, 4-dimethoxybenzophenone affords the corresponding diol, namely 1, 8-bis [bis (p-methoxyphenyl) hydroxymethyl] naphthalene (1)(Scheme1). Upon treatment with a mixture of aq [HBF4] and (CF3CO) 2O, this diol undergoes a double dehydroxylation reaction to afford the corresponding dication, 22+(Scheme 1). The 1H NMR spectrum of 22+ features the expected signals for a symmetrically peri-substituted naphthalene derivative: the signals for the hydrogen atoms at the 2-and 7-positions are shifted downfield by 1.05 ppm with respect to the analogous signals of 1. The appearance of four distinct signals for the hydrogen attached to the aromatic core of the p-methoxyphenyl groups indicates restricted rotation of the latter. The 13C resonance of the carbocationic centers appears at δ= 191.8 ppm, which is comparable to that observed for other carbocations such as bis (4-methoxyphenyl) phenylmethylium.[9] A single-crystal X-ray analysis [10] revealed the existence of a sterically congested structure (Figure1, top). The tight geometrical constraints present in the structure of 22+ induce distortions of the naphthalenediyl skeleton. Especially noteworthy are the C9-C8-C02 and C9-C1-C01 angles (125.36 (16) and 126.60 (15) 8, respectively) which are larger than the ideal value of 1208. As indicated by the sum of the bond angles at C01 (Æ (CC 01-C)= 359.6) and C02 (Æ (CC 02-C)= 359.8), each methylium center adopts a trigonal-planar arrangement. The trigonal coordination planes of the C01 and C02 centers form relatively large dihedral angles with the plane containing the naphthalene backbone (59.7 and 59.68, respectively), indicating that conjugation of the methylium center empty pz orbital with the π-system of the naphthalene backbone can only be modest. By contrast, the p-methoxyphenyl groups strongly stabilize the methylium centers, as indicated by the small dihedral angles that they form with the trigonal coordination planes of the C01 and C02 centers (18.1–28.58). This mesomeric stabilization is also reflected by the short C01ÀC11, C01ÀC21, C02ÀC31, and C02ÀC41 bonds. Finally, as a result of this unique molecular structure, the vicinal …