2022
DOI: 10.1021/jacs.1c13705
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2H-Imidazol-2-oneO-Oxide: A Criegee Intermediate from a σ0π2Singlet Ground-State Carbene

Abstract: Triplet carbenes and triplet molecular oxygen can combine to form singlet carbonyl O-oxide Criegee intermediates in an overall spin-allowed transformation. While this reaction runs at the diffusion limit in the case of triplet carbenes, singlet carbenes are commonly more reluctant to bind 3O2. In contradiction to this customarily encountered spin selectivity, the σ0π2 singlet ground-state carbene 2H-imidazol-2-ylidene 1 reacts extremely rapidly with 3O2 at temperatures as low as 30 K. The product of this cryog… Show more

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Cited by 13 publications
(11 citation statements)
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“…The sideways approach in the triplet transition state 3 TS add discussed earlier suggests that dichlorocarbene acts as an electrophile in its reaction with 3 O 2 . While this is in good agreement with the previously observed enhanced reactivity of highly electrophilic singlet carbenes, 25,26 nucleophilic N-heterocyclic carbenes (NHCs) were also reported to yield monoxidation products in their reaction with triplet molecular oxygen. 72 Thus, it seems worthwhile to study the impact of substitution on the 3 O 2 addition reaction in order to develop an understanding which singlet carbenes can undergo facile oxidation reactions.…”
Section: Resultssupporting
confidence: 90%
See 1 more Smart Citation
“…The sideways approach in the triplet transition state 3 TS add discussed earlier suggests that dichlorocarbene acts as an electrophile in its reaction with 3 O 2 . While this is in good agreement with the previously observed enhanced reactivity of highly electrophilic singlet carbenes, 25,26 nucleophilic N-heterocyclic carbenes (NHCs) were also reported to yield monoxidation products in their reaction with triplet molecular oxygen. 72 Thus, it seems worthwhile to study the impact of substitution on the 3 O 2 addition reaction in order to develop an understanding which singlet carbenes can undergo facile oxidation reactions.…”
Section: Resultssupporting
confidence: 90%
“…16–19 Yet, some singlet carbenes were still observed to react with molecular oxygen at experimentally relevant timescales in laser flash photolysis (LFP) studies, which is often explained by an initial thermal excitation of the carbene to its low-lying triplet state. 20–23 In a similar vein, some highly electrophilic singlet carbenes like difluorovinylidene 24,25 and 2 H -imidazol-2-ylidene 26,27 feature swift reactions with molecular oxygen even at cryogenic temperatures under matrix isolation conditions. However, a rapid oxygen addition reaction would usually not be expected for dichlorocarbene due to its high energy triplet state precluding an initial thermal excitation mechanism.…”
Section: Introductionmentioning
confidence: 98%
“…This comparative unreactivity arises from the long‐range repulsive interaction imparted by one of the partially occupied π* orbitals of 3 O 2 “attempting” to undergo in‐plane bonding with the more stable σ 2 π 0 configuration of the carbene. The σ 0 π 2 configuration of a carbene is usually of higher energy and thus uncommon, but recent work has identified the prompt reaction of 3 O 2 with the singlet 2H ‐imidazol‐2‐ylidene carbene with a σ 0 π 2 configuration to yield (after a fast ISC process) a stable singlet CI, even in an Ar matrix at 30 K (162).…”
Section: Electronic Absorption Spectroscopy Of Cismentioning
confidence: 99%
“… [16] So far, 2 H ‐imidazole‐2‐one O ‐oxide is the only known N‐heterocyclic Criegee intermediate which could be prepared from a σ 0 π 2 singlet ground state carbene under matrix isolation conditions (Figure 1b ). [17] However, the nitrogen atoms cannot act as donors in this case, because the respective lone‐pairs are perpendicular to the molecule's π‐system. Due to a lack of accessibility of urea oxides, we reckoned that their mono‐sulfur analogues, namely thiourea S ‐oxides, might serve as more easily available and potentially persistent model compounds for CIs; [18] therefore, we set out to examine the viability of their preparation via direct thiourea monoxidation (Figure 1b ).…”
Section: Introductionmentioning
confidence: 99%