Zhu Congqing, Xia Haiping
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), and College of Chemistry and Chemical Engineering , Xiamen University , Xiamen 361005 , China.
State Key Laboratory of Coordination Chemistry, Jiangsu Key Laboratory of Advanced Organic Materials, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China.
Acc Chem Res. 2018 Jul 17;51(7):1691-1700. doi: 10.1021/acs.accounts.8b00175. Epub 2018 Jun 21.
The construction of metal-carbon bonds is one of the most important issues of organometallic chemistry. However, the chelation of polydentate ligands to a metal via several metal-carbon bonds is rare. Metallapentalyne, which can be viewed as a 7-carbon (7C) chain coordinated to a metal via three metal-carbon bonds, was first reported in 2013. Although metallapentalyne contains a metal-carbon triple bond in a five-membered ring (5MR) and the bond angle around the carbyne carbon is only 129.5°, metallapentalyne exhibits excellent stability to air, moisture, and heat. Metallapentalyne possesses the rare planar Möbius aromaticity, which is in sharp contrast to the Hückel antiaromaticity in pentalyne. The metal fragment not only relieves the large ring strain present in pentalyne but also results in the transformation of the antiaromaticity in pentalyne to aromaticity in metallapentalyne. With the extension of the carbon chain from 7 to 12 carbon atoms, a series of novel polycyclic frameworks were constructed via the formation of several metal-carbon bonds. Some interesting phenomena were observed for these complexes. For instance, (1) the carbyne carbon of the 7C framework could react with both nucleophilic and electrophilic reagents, leading to the formation of 16- and 18-electron metallapentalenes; (2) σ aromaticity was first observed in an unsaturated system in the 8C framework; (3) two classical antiaromatic frameworks, cyclobutadiene and pentalene, were simultaneously stabilized in the 9C framework for the first time; (4) three fused 5MRs bridged by a metal are coplanar in the 10C framework; (5) the first [2 + 2 + 2] cycloaddition of a late transition metal carbyne complex with alkynes was realized during the construction of an 11C framework; (6) the largest number of carbon atoms coordinated to a metal atom in the equatorial plane was observed in the 12C framework; and (7) sharing of the transition metal by multiple aromatic units has seldom been observed in the metalla-aromatics. Therefore, the term carbolong chemistry has been used to describe the chemistry of these novel frameworks. More interestingly, carbolong complexes exhibit diverse properties, which could lead to potential future applications. As the discovery and creation of molecular fragments lead to advancements in chemistry, medical science, and materials chemistry, these novel polydentate carbon chain chelates might have important influences in these fields due to their facile synthesis, high stability, and unique properties.
金属 - 碳键的构建是有机金属化学中最重要的问题之一。然而，多齿配体通过多个金属 - 碳键与金属螯合的情况很少见。金属戊搭炔可以看作是通过三个金属 - 碳键与金属配位的7 - 碳（7C）链，于2013年首次报道。尽管金属戊搭炔在五元环（5MR）中含有金属 - 碳三键，且卡拜碳周围的键角仅为129.5°，但金属戊搭炔对空气、水分和热表现出优异的稳定性。金属戊搭炔具有罕见的平面莫比乌斯芳香性，这与戊搭炔中的休克尔反芳香性形成鲜明对比。金属片段不仅缓解了戊搭炔中存在的大环张力，还导致戊搭炔中的反芳香性转变为金属戊搭炔中的芳香性。随着碳链从7个碳原子扩展到12个碳原子，通过形成多个金属 - 碳键构建了一系列新颖的多环骨架。对于这些配合物观察到了一些有趣的现象。例如，（1）7C骨架的卡拜碳可以与亲核试剂和亲电试剂反应，导致形成16 - 和18 - 电子的金属戊搭炔；（2）在8C骨架的不饱和体系中首次观察到σ芳香性；（3）两种经典的反芳香骨架，环丁二烯和戊搭炔，首次在9C骨架中同时得到稳定；（4）在10C骨架中，由金属桥连的三个稠合5MR是共面的；（5）在构建11C骨架的过程中实现了后过渡金属卡拜配合物与炔烃的首次[2 + 2 + 2]环加成；（6）在12C骨架中观察到在赤道平面上与金属原子配位的碳原子数量最多；（7）在金属芳香化合物中很少观察到多个芳香单元共享过渡金属的情况。因此，“碳龙化学”一词已被用于描述这些新颖骨架的化学性质。更有趣的是，碳龙配合物表现出多样的性质，这可能导致潜在的未来应用。随着分子片段的发现和创造推动化学、医学和材料化学的进步，这些新颖的多齿碳链螯合物由于其简便的合成方法、高稳定性和独特性质，可能在这些领域产生重要影响。
