Synthesis of a Novel Lithocene that has Aromatic-like Nature with Non-aromatic Rings
Synthesis of a Novel Lithocene that has Aromatic-like Nature with Non-aromatic Rings
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具有非芳香环的类芳香性质的新型锂茂化合物的合成
DOI：
10.1002/asia.201100619
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
K. Ishimura and S. Nagase
中科院分区：
文献类型：
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作者：
M. Saito;T. Kuwabara;K. Ishimura and S. Nagase
含两个环戊二烯配体的茂金属，由于其独特的结构和催化活性，长期以来在有机金属化学中起着重要的作用。[1,2]虽然已经报道了许多含有过渡金属的茂金属的例子，但对相应的主族金属类似物的探索仍然较少。两种环戊二烯配体通过桥接基团连接同一金属，也显示出有趣的结构性质，并作为催化剂引起了广泛的关注由于环戊二烯基配体是芳香的，而且桥基位于芳香配体的同一平面上，所以不可能在没有桥基的情况下，两个环戊二烯基配体直接连接。与没有碳环原子金字塔化的芳香环戊二烯基配体相反，相应金属化合物的较重的14族原子被显著地金字塔化，从而导致它们的非芳香性。[4,5]我们最近报道了具有显著金字塔化锡中心的石锡石的合成和结构本文报道了一种新型中新世硅烷配体的合成和结构，该配体由Sn-Sn键直接连接，没有任何桥接基团。其有争议的芳香性也被证明。由相应的1,1 -二硫代丁烷与氯化叔丁基合成1,2 -二硫代丁烷[6a]，用[12]-冠-4在乙醚中处理[6a]，所得混合物重结晶得到具有新型中新世结构的中新世2，产率为72%（方案1），为橙红色晶体。通过x射线衍射分析确定了2的分子结构（图1）。其中一个锂原子与[12]-crown-4和乙醚分子配位，而另一个锂原子以η - 10的方式夹在两个斯坦诺环之间；这反映了其中新世构造。锂原子和碳原子在环上的距离（2.279（12）到2.431(12)）之间的差别很小，因此相互作用之间没有显著的差别。Sn-Li距离（2.766（10）和2.799(10)）比1（2.907(4)）短。[6a] 2（3.0255(16)）的Sn-Sn距离比对应的1（2.9652(3)）的Sn-Sn键略长，[6a]但明显比六苯基distannane（2.7635(14)）的Sn-Sn键长虽然两个锡环几乎是平面的，CÀC
The metallocenes bearing two cyclopentadienyl ligands that coordinate the same metal, have long played important roles in organometallic chemistry because of their unique structures as well as their catalytic activities.[1, 2] Although many examples of metallocenes bearing transition metals have already been reported, the corresponding maingroup metal analogs are still less explored. The ansa-metallocenes, in which each of the two cylopentadienyl ligands that coordinate the same metal connected by a bridging group, also reveal intriguing structural properties, and have attracted much attention as catalysts.[3] As the cyclopentadienyl ligand is aromatic and the bridging group is located on the same plane of the aromatic ligand, direct connection of two cyclopentadienyl ligands without any bridging groups is impossible. In contrast to the aromatic cyclopentadienyl ligands without pyramidarization of the carbon ring atoms, the heavier group 14 atoms of the corresponding metalloles are remarkably pyramidalized, thus leading to their nonaromatic characters.[4, 5] We have very recently reported on the synthesis and structures of lithiostannoles, which have remarkably pyramidalized tin centers.[6] We report herein the synthesis and structure of a novel lithocene bearing two stannole ligands that are directly connected by a Sn–Sn bond without any bridging groups. Its controversial aromaticity is also demonstrated.1, 2-Dilithiobistannole 1, prepared from the corresponding 1, 1-dilithiostannole with tert-butyl chloride,[6a] was treated with [12]-crown-4 in diethyl ether, and the resulting mixture was recrystallized to afford lithocene 2, which has a novel lithocene structure, as orange–red crystals in 72% yield (Scheme 1). The molecular structure of 2 was established by X-ray diffraction analysis (Figure1). One of the lithium atoms was coordinated with a [12]-crown-4 and a diethyl ether molecule, whereas the other lithium atom was sandwiched between the two stannole rings in a η10-fashion; this indicates its lithocene structure. The difference between the distances of the lithium and the carbon atoms on the rings (2.279 (12) to 2.431 (12)) is slight, and hence there is no remarkable difference between the interactions. The Sn–Li distances (2.766 (10) and 2.799 (10)) are shorter than those found in 1 (2.907 (4)).[6a] The Sn–Sn distance of 2 (3.0255 (16)) is slightly longer than the corresponding bond of 1 (2.9652 (3)),[6a] but is remarkably longer than the Sn–Sn bond of hexaphenyldistannane (2.7635 (14)).[7] Although the two stannole rings are almost planar, the CÀC