Resonance Balance Shift in Stacks of Delocalized Singlet Biradicals
Resonance Balance Shift in Stacks of Delocalized Singlet Biradicals
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DOI：
10.1002/anie.200901382
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发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Kubo, Takashi
中科院分区：
文献类型：
--
作者：
Shimizu, Akihiro;Uruichi, Mikio;Kubo, Takashi
最近，我们成功地分离了离域的单重态双根[1，2.利用苯基的自旋离域特性。[3]我们通过一维(1D)链中苯环的重叠，证明了单重态双自由基1具有很强的自旋-自旋相互作用，尽管闭合壳层的Kekul？结构1可以被画为一个共振贡献者(方案1)。[1B]Huang和Kertesz从理论的角度对自旋-自旋相互作用作了进一步的深入研究，并表明分子间的自旋-自旋相互作用比分子内的自旋-自旋相互作用更强。[4]这些实验和理论发现与非常重要的基本问题：非局部化的单态双基真的具有开壳性质吗？分子内的电子是否参与了分子间的共价键？在这项研究中，我们将证明分子内和分子间的自旋-自旋相互作用具有很强的相关性，并且可以通过施加外场来改变其大小。我们的建议是基于实验确定的2的分子结构、2的随温度变化的反射光谱和1的随压力变化的反射光谱。2的2-和10-位上的甲基，其中前线分子轨道的系数很小，预计会改变1中重叠的苯环之间的距离，因此，分子间自旋-自旋相互作用的大小应该受到影响。方案2概述了2的合成。3，10-和3，11-双(溴甲基)化合物3是按照以前报道的方法合成的。[1B]没有分离单独的异构体，因为这两个异构体都是单一的化合物2。双(2-甲基丙酸)衍生物5是用标准方法分三步得到的。5的酰氯衍生物与AlCl3进行Friedel-Craft环化反应得到二酮6，用NaBH4还原，然后用催化量的对甲苯磺酸脱水得到二氢化合物8。8与对氯苯醇脱氢得到绿色棱柱状的烃2。发现化合物2在室温下是稳定的固体。
Recently we succeeded in the isolation of delocalized singlet biradicals [1, 2] utilizing the spin-delocalizing character of the phenalenyl radical.[3] We demonstrated that the singlet biradical 1 has strong spin–spin interactions between molecules through the overlap of phenalenyl rings in the onedimensional (1D) chain even though the closed-shell KekulØ structure 1 can be drawn as a resonance contributor (Scheme 1).[1b] Huang and Kertesz gave further insight into the spin–spin interactions from a theroretical point of view and showed that the spin–spin interaction between the molecules was predicted to be stronger than that within the molecule.[4] These experimental and theoretical findings are associated with very fundamental issues: Do delocalized singlet biradicals actually have open-shell character? Are the electrons coupled within a molecule involved in covalent bonding between molecules? In this study we will demonstrate that intra-and intermolecular spin–spin interactions strongly correlate and can be altered in magnitude by an applied external field. Our proposal is based on the experimentally determined molecular structure of 2, a temperature-dependent reflection spectrum of 2, and a pressuredependent reflection spectrum of 1. Methyl groups at the2-and 10-positions in 2, where the frontier molecular orbital has very small coefficients, are expected to alter the distance between the overlapping phenalenyl rings with respect to the analogous separation in 1, and as a result, the magnitude of the intermolecular spin–spin interaction should be affected. The synthesis of 2 is outlined in Scheme 2. The 3, 10-and 3, 11-bis (bromomethyl) compounds 3 were synthesized according to the previously reported procedures.[1b] The individual isomers were not isolated because both were expected to lead to the single compound 2. Bis (2-methylpropionic acid) derivatives 5 were obtained in three steps by standard methods. Friedel–Crafts cyclization of the acyl chloride derivatives of 5 with AlCl3 afforded diketones 6. These were reduced with NaBH4 and subsequently dehydrated with a catalytic amount of p-toluenesulfonic acid to afford the dihydro compounds 8. Dehydrogenation of 8 with p-chloranil afforded the hydrocarbon 2 as green prisms. Compound 2 was found to be stable in the solid state at room temperature.