The Transition-Metal-Like Behavior of B-2(NHC)(2) in the Activation of CO: HOMO-LUMO Swap Without Photoinduction
The Transition-Metal-Like Behavior of B-2(NHC)(2) in the Activation of CO: HOMO-LUMO Swap Without Photoinduction
复制标题
B-2(NHC)(2) 在 CO 活化中的类过渡金属行为：无光诱导的 HOMO-LUMO 交换
DOI：
10.1002/anie.201805952
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发表时间：
2018
影响因子：
16.6
通讯作者：
Mo Yirong
中科院分区：
文献类型：
--
作者：
Zhang Huaiyu;Cao Zexing;Wu Wei;Mo Yirong
探索能与小分子相互作用的多键和不饱和主基化合物，以寻找非金属催化剂是当前的发展趋势。尤其是布伦瑞克。本文从新的理论角度探讨了B-2(NHC)(2)的成键性质及其对CO的活化机制。虽然B-2的基态是单键，但NHCs的接近将B-2激发到三键的第三激发态，两端有两个重要的西格玛孔。随后的静电吸引驱动B-2（NHC）的形成(2)。然而，B-2(NHC)(2)的两个键（HOMOs）中只有一个与CO的一个简并lumo相匹配。有趣的是，CO与B-2(NHC)(2)之间强烈的空间斥力导致后者的HOMO-LUMO交换。随后，B-2的HOMO和HOMO-1 (NHC)(2)都能有效地与CO的两个π *反键轨道（LUMO和LUMO+1）相互作用，导致大量电子回给和CO的最终活化。
It is a current trend to explore multi-bonded and unsaturated main group compounds that can interact with small molecules, in order to find non-metal catalysts. Notably, Braunschweig etal. found that diboryne stabilized by N-heterocyclic carbenes (NHCs) can bind and activate CO. Here we explore the bonding nature of B-2(NHC)(2) and its activation mechanism for CO from a novel theoretical perspective. While the ground state of B-2 is of a single bond, the approach of NHCs excites B-2 to its third excited state of a triple bond with two significant sigma-holes at the two ends. The subsequent electrostatic attraction drives the formation of B-2(NHC)(2). However, only one of the two bonds (HOMOs) of B-2(NHC)(2) fits to one of the degenerate LUMOs of CO. Interestingly, the strong steric repulsion between CO and B-2(NHC)(2) leads to the HOMO-LUMO swap in the latter. Subsequently, both HOMO and HOMO-1 of B-2(NHC)(2) can effectively interact with the two pi* anti-bonding orbitals (LUMO and LUMO+1) of CO, resulting in substantial electron back-donation and the ultimate activation of CO.