Bhagat Virinder, Schumann Julia, Bettinger Holger F
Institut für Organische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076, Tübingen, Germany.
Chemistry. 2020 Oct 1;26(55):12654-12663. doi: 10.1002/chem.202002445. Epub 2020 Sep 9.
The reaction of dioxygen with nitrenes can have significant energy barriers, although both reactants are triplet diradicals and the formation of nitroso-O-oxides is spin-allowed. By means of matrix-isolation infrared spectroscopy in solid argon, nitrogen, and neon, and through high-level computational quantum chemistry, it is shown herein that a 3-nitreno-1,3,2-benzodioxaborole CatBN (Cat=catecholato) reacts with dioxygen under cryogenic conditions thermally at temperatures as low as 7 K to produce two distinct products, an anti-nitroso-O-oxide and a nitritoborane CatBONO. The computed barriers for the formation of nitroso-O-oxide isomers are very low. Whereas anti-nitroso-O-oxide is kinetically trapped, its bisected isomer has a very low barrier for metathesis, yielding the CatBO+NO radicals in a strongly exothermic reaction; these radicals can combine under matrix-isolation conditions to give nitritoborane CatBONO. The trapped isomer, anti-nitroso-O-oxide, can form the nitritoborane CatBONO only after photoexcitation, possibly involving isomerization to the bisected isomer of anti-nitroso-O-oxide.
尽管双原子氧与氮宾都是三线态双自由基，且亚硝基 - O - 氧化物的形成在自旋方面是允许的，但双原子氧与氮宾的反应可能存在显著的能垒。本文通过在固态氩、氮和氖中进行基质隔离红外光谱研究，并借助高水平计算量子化学方法表明，一种3 - 氮宾 - 1,3,2 - 苯并二氧硼烷CatBN（Cat = 儿茶酚盐）在低温条件下，在低至7 K的温度下与双原子氧发生热反应，生成两种不同的产物，一种反式亚硝基 - O - 氧化物和一种亚硝基硼烷CatBONO。计算得出的亚硝基 - O - 氧化物异构体形成能垒非常低。虽然反式亚硝基 - O - 氧化物在动力学上被捕获，但其平分异构体的复分解能垒非常低，在强烈放热反应中生成CatBO + NO自由基；这些自由基在基质隔离条件下可以结合生成亚硝基硼烷CatBONO。被捕获的异构体反式亚硝基 - O - 氧化物只有在光激发后才能形成亚硝基硼烷CatBONO，这可能涉及异构化为反式亚硝基 - O - 氧化物的平分异构体。
