How to Make the σ0π2 Singlet the Ground State of Carbenes
How to Make the σ0π2 Singlet the Ground State of Carbenes
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DOI：
10.1021/ja407116e
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发表时间：
2013-09-18
影响因子：
15
通讯作者：
Borden, Weston Thatcher
中科院分区：
文献类型：
--
作者：
Chen, Bo;Rogachev, Andrey Yu.;Borden, Weston Thatcher
先前已经开发了成功的策略来稳定卡宾的sigma（2）pi（0）单重态相对于sigma（1）pi（1）三重态。然而，很少或根本没有注意到sigma（0）pi（2）单重态的稳定性。我们提出了两种简单的策略来稳定卡宾的sigma（2）pi（0）单重态，相对于sigma（2）pi（0）单重态和sigma（1）pi（1）三重态。这些策略包括通过两个相邻的sp（2）氮孤对电子使卡宾a轨道不稳定，以及通过将卡宾2 p-pi轨道并入含有两个双键的五元环或含有两个双键和具有低位空pi轨道的第六个原子的六元环来稳定卡宾2 p-pi轨道。已经进行了B3 LYP、CASPT 2和CCSD（T）计算，以评估这些策略在产生具有sigma（0）pi（6）单重态基态的环戊-2，4-二烯叉基和环己-2，5-二烯叉基的衍生物中的成功。讨论了2，5-二氮杂环戊二烯亚基（5）的σ（0）pi（6）单重基态与CH_2和CF_2的σ（2）pi（0）单重态的σ（2）pi（0）复合物的几何构型和结合能之间的差异。
Successful strategies have previously been developed to stabilize the sigma(2)pi(0) singlet states of carbenes, relative to sigma(1)pi(1) triplet states. However, little or no attention has been paid to the stabilization of the sigma(0)pi(2) singlet states. We present two simple strategies to stabilize the sigma(2)pi(0) singlet states of carbenes, relative to both the sigma(2)pi(0) singlet and sigma(1)pi(1) triplet states. These strategies consist of destabilization of the carbene a orbital by two, adjacent, sp(2) nitrogen lone pairs of electrons and stabilization of the carbene 2p-pi orbital by incorporating it into a five-membered ring, containing two double bonds, or into a six-membered ring, containing two double bonds and a sixth atom that has a low-lying empty pi orbital. B3LYP, CASPT2, and CCSD(T) calculations have been performed in order to assess the success of these strategies in creating derivatives of cyclopenta-2,4-dienylidene and cyclohexa-2,5-dienylidene with sigma(0)pi(6) singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the sigma(0)pi(6) singlet ground state of 2,5-diazacyclopentadienylidene (5) and the sigma(2)pi(0) singlet states of CH2 and CF2 are discussed.