An Extremely Electron Poor Cationic Triazoliumylidene N-Heterocyclic Carbene: Experimental and Computational Studies

Otto, Maximilian; Buhl, Hannes; Ganter, C.

doi:10.1021/acs.organomet.7b00670

Cited by 20 publications

(11 citation statements)

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“…An additional reason might be the better mesomeric stabilization of the anionic charge. A comparison of the HOMO/LUMO energies of the cationic NHC derived from imidazo[4,5‐ b ]pyridinium, of the 13 series reported here, of the reference NHC 1,3‐dimethylimidazol‐2‐ylidene, and the conjugated anionic sydnone carbene is displayed in Figure . These examples of NHCs cover the range from extremely π‐electron poor to extremely π‐electron rich.…”

Section: Resultsmentioning

confidence: 99%

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

et al. 2020

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Reaction of N-alkylated imidazoles with 2-chloro-4quinazolinone gave mesomeric betaines, 2-(1-alkyl-1H-imidazolium-3-yl)quinazolin-4-olates, for which three tautomeric forms of N-heterocyclic carbenes (NHCs) can be formulated, in addition to an anionic NHC after deprotonation. The NHC tautomers were trapped with sulfur, selenium, triethylborane, and triphenylborane as thiones, selenones and borane adducts, respectively. We obtained two isomers of the cyclic borane adducts, diazaboroloquinazolinones with [1,5-a] and [5,1-b]-type fusion between the quinazolinone and the diazaborole rings.[a] Scheme 3. Synthesis of the target betaines; 15 N-labeled atoms are marked in blue. Numbering. The index "b" stands for "mesomeric betaine". Scheme 4. Betaine, NHC tautomers and anionic NHC of 13. 452 stants (J C-N3 ) and by 1D 15 N NMR spectra (see Table S1 and Fig. S2, Supporting Information). The long-range 1 H-15 N couplings (J HN ) with 15 N labeled and unlabeled nitrogen atoms (at natural 15 Eur.

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Section: Resultsmentioning

confidence: 99%

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

et al. 2020

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“…The diverse carbene-related transformations highlight the indispensable role of carbene in organic synthesis, which also implies that the contributions from computational studies are highly appreciated. ,− Previous computational studies of metal carbene-mediated X–H insertion (X = C, N, O, etc. ) − and olefin metathesis − have shown that theoretical calculations can enable a better mechanistic understanding of carbene chemistry. − A summary of recent advances in theoretical studies would provide critical guidance for metal carbene formation and enlighten the rational design of new metal carbene transformation reactions.…”

Section: Introductionmentioning

confidence: 99%

Recent Advances in Theoretical Studies on Transition-Metal-Catalyzed Carbene Transformations

Lan

2021

Acc. Chem. Res.

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Conspectus Metal carbene plays a vital role in modern organic synthesis. The neutral divalent carbon of metal carbene renders it an active intermediate throughout a range of reactions. In experiments, diverse metal carbene-related transformation reactions have been established, including transition-metal-catalyzed cross-coupling reactions using N-heterocyclic carbenes as ligands, metal carbene insertion into σ bonds, cyclopropanations, ylide formation, and so forth. The remarkable progress achieved in synthetic chemistry, in turn, has increased the demand for mechanistic studies of carbene chemistry. A thorough understanding of reaction mechanisms can extend the application scope of metal carbene compounds and inspire the rational design of new carbene transformation reactions. Density functional theory (DFT) calculations have been performed in our group to gain more mechanistic insights into metal carbene-related reactions. This account focuses on computational studies of transition-metal-catalyzed carbene transformation reactions with nucleophiles. The generation of metal carbene or metal-ligated free carbene and subsequent carbene transformation pathways is discussed. According to our mechanistic studies of carbene transformation with nucleophiles, three generalized reaction models are summarized, including the intramolecular migratory insertion of metal carbene, intermolecular nucleophilic addition toward metal carbene, and outer-sphere nucleophilic addition to the metal-ligated free carbene. In general, the intermolecular nucleophilic addition mechanism is commonly proposed since metal carbene has an electrophilic carbene carbon. From a mechanistic point of view, the intramolecular migratory insertion mechanism is also widely used because metal carbene insertion into σ bonds formally occurs through this mechanism. An outer-sphere nucleophilic addition mechanism is proposed for reactions that form a metal-ligated free carbene complex instead of the commonly proposed metal carbene. The metal-ligated free carbene complex contains a naked carbene carbon that is not coordinated with the metal center. In this case, a transition-metal catalyst is used only as a Lewis acid, and nucleophilic addition occurs directly at the free carbene carbon. Our computational results suggested that outer-sphere nucleophilic addition is a facile step because metal ligation could stabilize the transition state as well as the generated intermediate. The intramolecular migratory insertion mechanism also has a low energy barrier due to the lack of an entropy penalty. Carbene formation from carbene precursors is usually the rate-determining step, except in intermolecular nucleophilic addition, and the reactivity of nucleophiles has a significant influence on the overall reaction rate. We can also envision that the weak nucleophilicity of nucleophiles would suppress outer-sphere nucleophilic addition. These computational studies showcase the characteristics of three carbene transformation models, and we hope that it will spur the developm...

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“…In 2017 César synthesized a cationic imidazolylidene NHC with an ammonium tag attached directly to the imidazole core [ 28 ]. Finally, in the same year Ganter described a triazoliumylidene with the formal +1 charge incorporated into the five-membered ring [ 29 ]. Several complexes formed by these carbenes have been also described, however, no ruthenium complexes with such carbenes have been synthesized.…”

Section: Introductionmentioning

confidence: 99%

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

Jawiczuk

Janaszkiewicz

Trzaskowski

2018

Beilstein J. Org. Chem.

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Cationic carbenes are a relatively new and rare group of ancillary ligands, which have shown their superior activity in a number of challenging catalytic reactions. In ruthenium-based metathesis catalysis they are often used as ammonium tags, to provide water-soluble, environment-friendly catalysts. In this work we performed computational studies on three cationic carbenes with the formal positive charge located at different distances from the carbene carbon. We show that the predicted initiation rates of Grubbs, indenylidene, and Hoveyda–Grubbs-like complexes incorporating these carbenes show little variance and are similar to initiation rates of standard Grubbs, indenylidene, and Hoveyda–Grubbs catalysts. In all investigated cases the partial charge of the carbene carbon atom is similar, resulting in comparable Ccarbene–Ru bond strengths and Ru–P/O dissociation Gibbs free energies.

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An Extremely Electron Poor Cationic Triazoliumylidene N-Heterocyclic Carbene: Experimental and Computational Studies

Cited by 20 publications

References 100 publications

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

Betaine–N‐Heterocyclic Carbene Interconversions of Quinazolin‐4‐One Imidazolium Mesomeric Betaines. Sulfur, Selenium, and Borane Adduct Formation

Recent Advances in Theoretical Studies on Transition-Metal-Catalyzed Carbene Transformations

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

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