Unusual Nitrene Oxidation Product Formation by Metathesis Involving the Dioxygen O−O and Borylnitrene B−N Bonds

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.
Overcoming barriers: The reaction of dioxygen with nitrenes can have significant energy barriers. The reaction mechanism of borylnitrene 1 is investigated through matrix‐isolation infrared spectroscopy and high‐level computational quantum chemistry. Borylnitrene 1 reacts with dioxygen to form nitritoborane 3 a via nitroso‐O‐oxide isomer 2 c. Nitroso‐O‐oxide isomer 2 a is stable towards thermal reaction to 3 a, but dyotropic rearrangement can be achieved photochemically.