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

Abstract

The reactiono fd ioxygen with nitrenes can have significant energy barriers, although both reactants are triplet diradicals and the formationof nitroso-O-oxides is spin-allowed.B ym eans of matrix-isolation infrared spectroscopy in solid argon, nitrogen, and neon,a nd through high-level computational quantum chemistry,i ti ss hownh erein that a 3-nitreno-1,3,2-benzodioxaborole CatBN (Cat = catecholato) reacts with dioxygenu nder cryogenicc onditions thermally at temperatures as low as 7K to produce two distinct products, an anti-nitroso-O-oxide and an itritoborane CatBONO. The computedb arriers for the formation of nitroso-O-oxide isomersa re very low.W hereas anti-nitroso-O-oxide is kinetically trapped,i ts bisected isomer has av ery low barrierf or metathesis, yieldingt he CatBO + NO radicals in as trongly exothermic reaction; these radicals can combineu nder matrix-isolation conditions to give nitritoborane CatBONO. The trapped isomer, anti-nitroso-O-oxide, can form the nitri-toboraneC atBONO only after photoexcitation, possibly involvingi somerization to the bisectedi somer of anti-nitroso-O-oxide.

The Reaction of CO2 with a Borylnitrene: Formation of an 3‐Oxaziridinone

“… [34] Nitrenes are analogues of carbenes that generally undergo similar reactions, but for these the related cycloaddition reaction with CO 2 was never demonstrated. We have previously identified a class of particularly reactive nitrenes, borylnitrenes, carrying two oxygen atoms at the boron center that preclude isomerization to iminoboranes [35–41] . The catechol derivative 3 (CatBN, Cat=catecholato), accessible under matrix isolation conditions from azide 4 (Scheme 1 b), has a triplet electronic ground state ( 3 A 2 ‐ 3 ) and shows high reactivity towards small molecules even under matrix isolation conditions (N 2 , CO, D 2 , CH 4 , O 2 ) [35–41] .…”

“…We have previously identified a class of particularly reactive nitrenes, borylnitrenes, carrying two oxygen atoms at the boron center that preclude isomerization to iminoboranes. [35][36][37][38][39][40][41] The catechol derivative 3 (CatBN, Cat = catecholato), accessible under matrix isolation conditions from azide 4 (Scheme 1 b), has a triplet electronic ground state ( 3 A 2 -3) and shows high reactivity towards small molecules even under matrix isolation conditions (N 2 , CO, D 2 , CH 4 , O 2 ). [35][36][37][38][39][40][41] The reaction with closed-shell molecules requires photoactivation (l > 550 nm) presumably involving the closed-shell singlet state (S 1 ) 1 A 1 -3.…”

“…[35][36][37][38][39][40][41] The catechol derivative 3 (CatBN, Cat = catecholato), accessible under matrix isolation conditions from azide 4 (Scheme 1 b), has a triplet electronic ground state ( 3 A 2 -3) and shows high reactivity towards small molecules even under matrix isolation conditions (N 2 , CO, D 2 , CH 4 , O 2 ). [35][36][37][38][39][40][41] The reaction with closed-shell molecules requires photoactivation (l > 550 nm) presumably involving the closed-shell singlet state (S 1 ) 1 A 1 -3. The electronic structure of 1 A 1 -3 is reminiscent of vinylidenes as their reactive centers are related by an isoelectronic substitution of the C = C by the B = N unit (Scheme 1 c).…”

The Reaction of CO2 with a Borylnitrene: Formation of an 3‐Oxaziridinone

“…We have previously identified a class of particularly reactive nitrenes, borylnitrenes, carrying two oxygen atoms at the boron center that preclude isomerization to iminoboranes. [ 35 , 36 , 37 , 38 , 39 , 40 , 41 ] The catechol derivative 3 (CatBN, Cat=catecholato), accessible under matrix isolation conditions from azide 4 (Scheme 1 b ), has a triplet electronic ground state ( 3 A 2 ‐ 3 ) and shows high reactivity towards small molecules even under matrix isolation conditions (N 2 , CO, D 2 , CH 4 , O 2 ). [ 35 , 36 , 37 , 38 , 39 , 40 , 41 ] The reaction with closed‐shell molecules requires photoactivation ( λ >550 nm) presumably involving the closed‐shell singlet state (S 1 ) 1 A 1 ‐ 3 .…”

“…[ 35 , 36 , 37 , 38 , 39 , 40 , 41 ] The catechol derivative 3 (CatBN, Cat=catecholato), accessible under matrix isolation conditions from azide 4 (Scheme 1 b ), has a triplet electronic ground state ( 3 A 2 ‐ 3 ) and shows high reactivity towards small molecules even under matrix isolation conditions (N 2 , CO, D 2 , CH 4 , O 2 ). [ 35 , 36 , 37 , 38 , 39 , 40 , 41 ] The reaction with closed‐shell molecules requires photoactivation ( λ >550 nm) presumably involving the closed‐shell singlet state (S 1 ) 1 A 1 ‐ 3 . The electronic structure of 1 A 1 ‐ 3 is reminiscent of vinylidenes as their reactive centers are related by an isoelectronic substitution of the C=C by the B=N unit (Scheme 1 c ).…”