Elusiveness of bishomoaromaticity in anionic systems: the bicyclo[3.2.1]octa-3,6-dien-2-yl anion

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Stabilization of the alleged bishomoromatic bicyclo[3.2.1]octa-2,6-dienyl anion by counterion interactions and by hyperconjugation

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution

Planar Möbius aromatic pentalenes incorporating 16 and 18 valence electron osmiums

夏海平课题组长期致力于芳香体系的拓展研究。作为金属杂戊搭炔化学又一重要进展，在此研究中，他们发现金属杂戊搭炔的卡拜碳原子宛如“变色龙”，既具有亲核性，又具有亲电性。通过金属杂戊搭炔与亲电试剂反应揭示了其三键迁移的神秘面纱，并成功地捕捉了三键迁移的中间体——金属中心为16电子的金属杂戊搭烯；通过金属杂戊搭炔与亲核试剂反应，得到金属中心为18电子的金属杂戊搭烯。 　　朱军课题组通过理论计算，对金属杂戊搭烯进行深入理论研究。发现金属中心16电子、18电子金属杂戊搭烯均具有芳香性。深入的CMO-NICS计算表明，本质上，金属杂戊搭炔中Mobius芳香性来源于金属杂戊搭烯，正如苯炔的芳香性来源于苯。Mobius芳香性自1958年提出以来，实际合成的例子稀少，且前人已分离并报道的Möbius芳香体系均具有扭曲的拓扑结构。金属杂戊搭烯/炔代表着一类平面型的Möbius芳香性体系。从而颠覆了传统的芳香化学，为构筑其他平面型Möbius芳香体系奠定了基础。 　　该工作的合成和结构表征是在夏海平教授指导下由博士生朱从青（第一作者）、罗明和硕士生朱琴完成，我校温庭斌教授参与了产物结构表征的讨论。理论计算由朱军副教授完成，我校吕鑫教授、美国佐治亚大学P.v.R.Schleyer教授和J.I-C.Wu博士也参与了芳香性的讨论。Aromaticity, a highly stabilizing feature of molecules with delocalized electrons in closed circuits, is generally restricted to ‘Hückel’ systems with 4n+2 mobile electrons. Although the Möbius concept extends the principle of aromaticity to 4n mobile electron species, the rare known examples have complex, twisted topologies whose extension is unlikely. Here we report the realization of osmapentalenes, the first planar Möbius aromatic complexes with 16 and 18 valence electron transition metals. The Möbius aromaticity of these osmapentalenes, documented by X-ray structural, magnetic and theoretical analyses, demonstrates the basis of the aromaticity of the parent osmapentalynes. All these osmapentalenes are formed by both electrophilic and nucleophilic reactions of the in-plane π component of the same carbyne carbon, illustrating ambiphilic carbyne reactivity, which is seldom observed in transition metal chemistry. Our results widen the scope of Möbius aromaticity dramatically and open prospects for the generalization of planar Möbius aromatic chemistry.国家自然科学基金委、科技部和美国科学基金会的资