Department of Chemistry and the Center for Advanced, Scientific Computing and Modeling, University of North Texas , 1155 Union Circle, #305070, DentonTexas, 76203-5070, United States.
J Am Chem Soc. 2013 Sep 18;135(37):13954-64. doi: 10.1021/ja407116e. Epub 2013 Sep 5.
Successful strategies have previously been developed to stabilize the σ(2)π(0) singlet states of carbenes, relative to σ(1)π(1) triplet states. However, little or no attention has been paid to the stabilization of the σ(0)π(2) singlet states. We present two simple strategies to stabilize the σ(0)π(2) singlet states of carbenes, relative to both the σ(2)π(0) singlet and σ(1)π(1) triplet states. These strategies consist of destabilization of the carbene σ orbital by two, adjacent, sp(2) nitrogen lone pairs of electrons and stabilization of the carbene 2p-π 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 π 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 σ(0)π(6) singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the σ(0)π(6) singlet ground state of 2,5-diazacyclopentadienylidene (5) and the σ(2)π(0) singlet states of CH2 and CF2 are discussed.
先前已经开发出了成功的策略来稳定卡宾的 σ(2)π(0)单线态，相对于 σ(1)π(1)三线态。然而，对于 σ(0)π(2)单线态的稳定化，几乎没有或没有给予关注。我们提出了两种简单的策略来稳定卡宾的 σ(0)π(2)单线态，相对于 σ(2)π(0)单线态和 σ(1)π(1)三线态。这些策略包括通过两个相邻的 sp(2)氮孤对电子来使卡宾 σ 轨道去稳定化，以及通过将其并入包含两个双键的五元环或包含两个双键和第六个具有低占据空 π 轨道的原子的六元环中来使卡宾 2p-π 轨道稳定化。为了评估这些策略在创造具有 σ(0)π(6)单线态基态的环戊二烯亚基和环己二烯亚基衍生物方面的成功，进行了 B3LYP、CASPT2 和 CCSD(T)计算。讨论了计算出的 2,5-二氮杂环戊二烯基亚基（5）的 Xe 配合物的 σ(0)π(6)单线态基态的计算几何形状和结合能与 CH2 和 CF2 的 σ(2)π(0)单线态之间的差异。
