Probing hyperconjugative aromaticity in 2H-pyrrolium and cyclopentadiene containing group 9 transition metal substituents: bridged carbonyl ligands can enhance aromaticity.
Probing hyperconjugative aromaticity in 2H-pyrrolium and cyclopentadiene containing group 9 transition metal substituents: bridged carbonyl ligands can enhance aromaticity.
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DOI：
10.1039/d0cp06388f
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发表时间：
2021-01
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影响因子：
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通讯作者：
Jie Zeng;Yu Zhao;Fangzhou Xu;Jun Zhu
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文献类型：
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作者：
Jie Zeng;Yu Zhao;Fangzhou Xu;Jun Zhu
芳香性和超共轭是有机化学中的两个基本概念。通过将这两个概念结合在一起，产生的超共轭芳香性引起了理论和计算化学家的极大关注。然而，以往的研究主要集中在主基团化学上。对于过渡金属化学中的超共轭芳构性，目前的研究仅限于第10和第11基团。本文通过密度泛函理论计算，证明了含9族过渡金属取代基的2h -吡咯和环戊二烯可以实现超共轭芳构性。更重要的是，进一步的研究表明，两个取代基之间的金属-金属键相互作用可以降低超共轭芳香性，而桥接羰基配体由于CR2片段的HOMO轨道显著升高而增强芳香性。这些发现不仅扩展了超共轭芳构性概念的范围，而且有助于金属芳构化学的发展。
Aromaticity and hyperconjugation are two fundamental concepts in organic chemistry. By combination of the two concepts together, the resulting hyperconjugative aromaticity has attracted considerable attention from both theoretical and computational chemists. However, previous studies are mainly focused on the main group chemistry. For the hyperconjugative aromaticity in the transition metal chemistry, the studies are limited to groups 10 and 11. Here, we demonstrate that hyperconjugative aromaticity can be achieved in 2H-pyrrolium and cyclopentadiene containing group 9 transition metal substituents via density functional theory calculations. More importantly, further studies reveal that the metal-metal bonding interaction between two substituents could reduce hyperconjugative aromaticity, whereas the bridged carbonyl ligands will enhance aromaticity due to the significantly elevated HOMO orbital of the CR2 fragment. All these findings not only extend the scope of the concept of hyperconjugative aromaticity but also are helpful to develop the chemistry of metalla-aromatics.