N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons

Rottschäfer, Dennis; Ho, Nga Kim T.; Neumann, Beate; Stammler, Hans‐Georg; Gastel, Maurice van; Andrada, Diego M.; Ghadwal, Rajendra S.

doi:10.1002/ange.201713346

Cited by 17 publications

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References 65 publications

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“…Chichibabin’s, Dimroth’s, and Müller’s hydrocarbons, novelties in their time, have become exemplars of another extension, now linear, of quinoid hydrocarbons (Figure ). − In some of the compounds made, the radical character may reside on heteroatoms …”

Section: Some Typical Diradicals and Diradicaloidsmentioning

confidence: 99%

Do Diradicals Behave Like Radicals?

et al. 2019

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This review sets out to understand the reactivity of diradicals and how that may differ from monoradicals. In the first part of the review, we delineate the electronic structure of a diradical with its two degenerate or nearly degenerate molecular orbitals, occupied by two electrons. A classification of diradicals based on whether or not the two SOMOs can be located on different sites of the molecule is useful in determining the ground state spin. Important is a delocalized to localized orbital transformation that interchanges “closed-shell” to “open-shell” descriptions. The resulting duality is useful in understanding the dual reactivity of singlet diradicals. In the second part of the review, we examine, with a consistent level of theory, activation energies of prototypical radical reactions (dimerization, hydrogen abstraction, and addition to ethylene) for representative organic diradicals and diradicaloids in their two lowest spin states. Differences and similarities in reactivity of diradicals vs monoradicals, based on either a localized or delocalized view, whichever is suitable, are then discussed. The last part of this review begins with an extensive, comparative, and critical survey of available measures of diradical character and ends with an analysis of the consequences of diradical character for selected diradicaloids.

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Section: Some Typical Diradicals and Diradicaloidsmentioning

confidence: 99%

Do Diradicals Behave Like Radicals?

et al. 2019

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CAAC‐Based Thiele and Schlenk Hydrocarbons

et al. 2020

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Diradicals have been of tremendous interest for over a century ever since the first reports of p‐ and m‐phenylene‐bridged diphenylmethylradicals in 1904 by Thiele and 1915 by Schlenk. Reported here are the first examples of cyclic(alkyl)(amino)carbene (CAAC) analogues of Thiele's hydrocarbon, a Kekulé diradical, and Schlenk's hydrocarbon, a non‐Kekulé diradical, without using CAAC as a precursor. The CAAC analogue of Thiele's hydrocarbon has a singlet ground state, whereas the CAAC analogue of Schlenk's hydrocarbon contains two unpaired electrons. The latter forms a dimer, by an intermolecular double head‐to‐tail dimerization. This straightforward synthetic methodology is modular and can be extended for the generation of redox‐active organic compounds.

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Nickel‐katalysierte intramolekulare 1,2‐Aryl‐Wanderung von mesoionischen Carbenen (iMICs)

et al. 2020

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Die Ni‐katalysierte intramolekulare 1,2‐Verschiebung eines 2,6‐Diisopropylphenyl‐Substituenten (Dipp) von sieben mesoionischen Carbenen (iMICAr) 2 a–g (iMICAr=ArC{N(Dipp)}2CHC; Ar=Aryl) unter Bildung von 1,3‐Imidazolen (IMDAr) 3 a–g (IMDAr=ArC{N(Dipp)CHC(Dipp)N}) wird berichtet. Dieser Prozess impliziert die Spaltung einer N‐CDipp‐Bindung in 2 und die anschließende Knüpfung einer C‐CDipp‐Bindung, was in der NHC‐Chemie bislang unbekannt war. Die Überführung von 3 in Super‐iMICs (5) (S‐iMIC=ArC{N(Dipp)N(Me)C(Dipp)}C) wurde mit der Herstellung von Selen‐ (6), Gold‐(7) und Palladium‐Derivaten (8) gezeigt. Die Quantifizierung der stereoelektronischen Eigenschaften lässt hierbei eine deutliche Erhöhung der σ‐Donorstärke von 5 relativ zu klassischen NHCs erkennen. Bemerkenswert hierbei ist das “Buried Volume” von 5 (%Vbur=45), welches in iMICs dem bisher größten bekannten Wert entspricht. Katalytische Studien weisen auf eine hervorragende Aktivität von 5 hin, was mit den stereoelektronischen Eigenschaften der Liganden im Einklang ist.

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N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons

Cited by 17 publications

References 65 publications

Do Diradicals Behave Like Radicals?

Do Diradicals Behave Like Radicals?

CAAC‐Based Thiele and Schlenk Hydrocarbons

Nickel‐katalysierte intramolekulare 1,2‐Aryl‐Wanderung von mesoionischen Carbenen (iMICs)

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