Mieres-Perez Joel, Costa Paolo, Mendez-Vega Enrique, Crespo-Otero Rachel, Sander Wolfram
Lehrstuhl für Organische Chemie II , Ruhr Universität Bochum , 44780 Bochum , Germany.
School of Biological and Chemical Sciences , Queen Mary University London , Mile End Road , London E1 4NS , U.K.
J Am Chem Soc. 2018 Dec 12;140(49):17271-17277. doi: 10.1021/jacs.8b10792. Epub 2018 Nov 30.
The chemistry of arylnitrenes is dominated by their triplet ground states and excited open-shell singlet states. This results in radical-type reactions and unwanted rearrangements, which diminish the use of arylnitrenes as intermediates in organic synthesis. While the closed-shell singlet states of arylnitrenes are expected to undergo useful chemical transformations (comparable to the closed-shell singlet states of carbenes), these states are too high in energy to be chemically accessible. When triplet pentafluorophenylnitrene is interacting with the Lewis acid BF under the conditions of matrix isolation, a Lewis acid-base complex consisting of the closed-shell singlet state of the nitrene and two molecules of BF is formed. Although the closed-shell singlet state of pentafluorophenylnitrene is calculated (CCSD(T)) to lie more than 25 kcal/mol above its triplet ground state, the reaction with BF results in switching the spin state from triplet to singlet. The formation of the singlet complex was monitored by IR, UV-vis, and EPR spectroscopy. DFT, CCSD(T), and CASPT2 calculations confirm the experimental findings.
芳基氮宾的化学性质主要由其三重态基态和激发态开壳单重态决定。这导致了自由基型反应和不必要的重排，从而减少了芳基氮宾作为有机合成中间体的应用。虽然芳基氮宾的闭壳单重态有望发生有用的化学转化（类似于卡宾的闭壳单重态），但这些态的能量过高，无法通过化学方法获得。当三重态五氟苯基氮宾在基质隔离条件下与路易斯酸BF相互作用时，会形成一种由氮宾的闭壳单重态和两分子BF组成的路易斯酸碱络合物。尽管计算得出（CCSD(T)）五氟苯基氮宾的闭壳单重态比其三重态基态高出超过25千卡/摩尔，但与BF的反应导致自旋态从三重态转变为单重态。通过红外光谱、紫外可见光谱和电子顺磁共振光谱监测了单重态络合物的形成。密度泛函理论（DFT）、耦合簇单双激发（CCSD(T)）和完全活性空间自洽场二阶微扰理论（CASPT2）计算证实了实验结果。
