The transformations of a methylene-bridged bis-triazolium salt: a mesoionic carbene based metallocage and analogues of TCNE and NacNac

Stubbe, Jessica; Suhr, Simon; Beerhues, Julia; Nößler, Maite; Sarkar, Biprajit

doi:10.1039/d0sc06957d

Cited by 10 publications

(3 citation statements)

References 71 publications

(31 reference statements)

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“…Furthermore, we could show that the triazolylidene unit is crucial for the stabilisation of the radical and acts as a superior electron acceptor compared to the NHC unit. These results, combined with related findings of radical stabilization by MIC units, [23,30,25] open up interesting questions regarding the π‐accepting properties of mesoionic carbenes. Additionally, the synthetic route presented by us for generating azide‐substituted 1,2,3‐triazolium salts should be easily transferable to other 1,2,3‐triazolium salts whose synthesis is modular.…”

Section: Discussionmentioning

confidence: 68%

Azide‐Substituted 1,2,3‐Triazolium Salts as Useful Synthetic Synthons: Access to Triazenyl Radicals and Staudinger Type Reactivity

Stein

Suhr

Hazari

et al. 2023

Chemistry A European J

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Mesoionic carbenes (MIC) are a popular class of compound that are heavily investigated at the moment. The access to cationic MICs, and the ability of MICs to stabilize radicals are two highly attractive fields that have hardly been explored until now. Here the synthesis and characterisation of three different cationic azide-substituted 1,2,3-triazolium salts, used as building blocks for studying their reactivity towards triphenylphosphine are reported, where the reactivity is dependent on the nature of the starting triazolium salt. Furthermore, the cationic triazolium salts were used to develop a series of unsymmetrical MIC-triazene-NHC/MIC' compounds, which can be readily converted to the radical form either by electrochemical or chemical methods. These radicals, which display NIR electrochromism, were investigated using a battery of techniques such as electrochemistry, UV/Vis/NIR and EPR spectroelectrochemistry, and theoretical calculations. Interestingly, the MIC plays an important role in the stabilization of the triazenyl radical, particularly in a competitive role vis-à-vis their NHC counterparts. These results shed new light on the ability of MICs to stabilize radicals, and possibly also on their π-accepting ability.

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Section: Discussionmentioning

confidence: 68%

Azide‐Substituted 1,2,3‐Triazolium Salts as Useful Synthetic Synthons: Access to Triazenyl Radicals and Staudinger Type Reactivity

Stein

Suhr

Hazari

et al. 2023

Chemistry A European J

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“…42 It is worth mentioning that methylene-bridged bis-triazolium salts have been shown to undergo significant structural changes and chemical transformations under metalation conditions with silver oxide. 43 An elegant work reported by Sarkar and coworkers described the unexpected formation of a new bismesoionic carbene ligand, obtained through activation of the methylene protons of the CH 2 linker when a bis-triazolium salt was treated with Ag 2 O. 43 Intrigued by this work, we decided to isolate the Ag-bis-triazolylidene complex generated by reaction of L1H 2 (Br) 2 with Ag 2 O under the conditions used in the synthesis of Mn1.…”

Section: ■ Introductionmentioning

confidence: 99%

“…43 An elegant work reported by Sarkar and coworkers described the unexpected formation of a new bismesoionic carbene ligand, obtained through activation of the methylene protons of the CH 2 linker when a bis-triazolium salt was treated with Ag 2 O. 43 Intrigued by this work, we decided to isolate the Ag-bis-triazolylidene complex generated by reaction of L1H 2 (Br) 2 with Ag 2 O under the conditions used in the synthesis of Mn1. Interestingly, we confirmed that the major product obtained in this reaction corresponds to the expected Ag-bis-triazolylidene adduct (Figures S16 and S17).…”

Section: ■ Introductionmentioning

confidence: 99%

Bis-Triazolylidenes of Manganese and Rhenium and Their Catalytic Application in N-Alkylation of Amines with Alcohols

2023

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A new family of air-stable Mn and Re complexes bearing bidentate bis(1,2,3-triazol-5-ylidene) ligands with the general formula [M(bis-triazolylidene)(CO)3X] (M = Mn or Re; X = Cl or Br), containing a methylene linker or a direct link between the two triazolylidene ligands, is presented. All complexes have been applied as catalysts for the N-alkylation of anilines with benzylic alcohols. The Mn complex bearing a bis-triazolylidene with a methylene bridge between the two triazolylidene fragments was shown to be a highly efficient catalyst, affording the corresponding amine in 92% yield in the presence of a low base loading (t-BuOK, 0.1 equiv). Comparison between Mn complexes bearing imidazolium- and triazolium-derived N-heterocyclic carbene ligands showed that Mn triazolylidenes displayed higher catalytic activity when a low base loading was used.

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Gauging Radical Stabilization with Carbenes

et al. 2022

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Carbenes, including N‐heterocyclic carbene (NHC) ligands, are used extensively to stabilize open‐shell transition metal complexes and organic radicals. Yet, it remains unknown, which carbene stabilizes a radical well and, thus, how to design radical‐stabilizing C‐donor ligands. With the large variety of C‐donor ligands experimentally investigated and their electronic properties established, we report herein their radical‐stabilizing effect. We show that radical stabilization can be understood by a captodative frontier orbital description involving π‐donation to‐ and π‐donation from the carbenes. This picture sheds a new perspective on NHC chemistry, where π‐donor effects usually are assumed to be negligible. Further, it allows for the intuitive prediction of the thermodynamic stability of covalent radicals of main group‐ and transition metal carbene complexes, and the quantification of redox non‐innocence.

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The transformations of a methylene-bridged bis-triazolium salt: a mesoionic carbene based metallocage and analogues of TCNE and NacNac

Abstract: Unusual and unexpected chemical transformations often provide access to completely new types of functional molecules. We report here the synthesis of a methylene-bridged bis-triazolium salt designed as a precursor for...

Cited by 10 publications

References 71 publications

Azide‐Substituted 1,2,3‐Triazolium Salts as Useful Synthetic Synthons: Access to Triazenyl Radicals and Staudinger Type Reactivity

Azide‐Substituted 1,2,3‐Triazolium Salts as Useful Synthetic Synthons: Access to Triazenyl Radicals and Staudinger Type Reactivity

Bis-Triazolylidenes of Manganese and Rhenium and Their Catalytic Application in N-Alkylation of Amines with Alcohols

Gauging Radical Stabilization with Carbenes

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