Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands) and.
Institute for Molecules and Materials (IMM), Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
ChemistryOpen. 2021 Aug;10(8):784-789. doi: 10.1002/open.202100172.
Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) "Pauli-lowering catalysis" for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) "LUMO-lowering catalysis" for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in IED interactions. In all, we illustrate how the novel concept of "Pauli-lowering catalysis" can be overruled by the traditional concept of "LUMO-lowering catalysis" when the degree of LUMO stabilization is extreme as in the case of multi-protonated 2-aza-dienes.
布朗斯特酸催化的逆电子需求（IED）氮杂-Diels-Alder 反应在 2-氮杂二烯和乙烯之间进行，使用量子化学计算进行了研究。计算得到的活化能随着二烯的碱性位逐渐质子化而系统地降低。我们的活化应变和 Kohn-Sham 分子轨道分析追踪了这种增强反应性的起源，即 i）对于单质子化的 2-氮杂二烯，由于诱导异步但仍然协同的反应途径，降低了反应物之间的 Pauli 斥力，从而产生了“Paul 降低催化”；和 ii）对于多质子化的 2-氮杂二烯，由于其高度稳定的 LUMO（s）和更协同的同步反应路径，促进了 IED 相互作用中更有效的轨道重叠，从而产生了“LUMO 降低催化”。总之，我们说明了当 LUMO 稳定度极高，如多质子化的 2-氮杂二烯的情况，“Paul 降低催化”的新概念如何被传统的“LUMO 降低催化”概念所推翻。
