Wang Zhi-Xiang, Zhang Cheng-Gen, Chen Zhongfang, Schleyer Paul von Ragué
College of Chemistry and Chemical Engineering, Graduate University of Chinese Academy of Sciences, Beijing, P. R. China.
Inorg Chem. 2008 Feb 18;47(4):1332-6. doi: 10.1021/ic7017709. Epub 2008 Jan 19.
Planar tetracoordinate carbon (ptC) arrangements can be achieved by employing multiple substituents based on beryllium, despite its rather weak pi-acceptor ability. A variety of ptC-containing examples, some with more than one ptC, have been designed computationally by elaborating the planar C(BeH) 4 (2-) prototype at B3LYP/6-311++G(3df,2p) and MP2/6-311++G(3df,2p) levels of theory for some small ptC representatives. The prototype prefers a D(2h) paramagnetic triplet ground state due to Hund's rule, rather than a singlet. The highly polarized C-Be bonding weakens the rigidity of the tetrahedral carbon in T(d)C(BeH) 4 enormously, and the enhancement of both C-Be and Be 4 peripheral covalent bonding exerted by the extra electrons stabilizes the ptC eventually. The delocalization of the two p pi electrons is only modest, but their density on the most electronegative carbon atom helps stabilize the ptC arrangement. This is in contrast to the conventional strategy to delocalize p(pi) lone pairs for stabilizing the ptC arrangement. Various strategies to achieve neutral derivatives with ptCs are demonstrated.
尽管铍的π受体能力较弱，但通过使用多个基于铍的取代基可以实现平面四配位碳（ptC）结构。通过在B3LYP/6 - 311++G(3df,2p)和MP2/6 - 311++G(3df,2p)理论水平上对一些小的ptC代表物详细阐述平面C(BeH)₄²⁻原型，已经通过计算设计了各种含ptC的例子，有些例子含有不止一个ptC。由于洪德规则，该原型更倾向于D(2h)顺磁三重态基态，而不是单重态。高度极化的C - Be键极大地削弱了T(d)C(BeH)₄中四面体碳的刚性，并且额外电子对C - Be和Be₄外围共价键的增强最终稳定了ptC。两个pπ电子的离域程度仅适中，但它们在电负性最强的碳原子上的密度有助于稳定ptC结构。这与传统的使p(π)孤对离域以稳定ptC结构的策略形成对比。展示了实现含ptC中性衍生物的各种策略。
