Reductive Elimination at Carbon under Steric Control

Tolentino, Daniel R.; Neale, Samuel E.; Isaac, Connie J.; Macgregor, Stuart A.; Whittlesey, Michael K.; Jazzar, Rodolphe; Bertrand, Guy

doi:10.1021/jacs.9b04957

Cited by 49 publications

(51 citation statements)

References 41 publications

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“…[12] Formal reductive elimination from NHC derivatives on steric grounds is documented in the literature,a nd in the case of 3-5 we assume that the steric bulk of the added base is the driving force for regenerating the free carbene. [13] We would like to point out, that while analysing the degradation of 2,w ecould not observe any evidence for aW anzlick-type dimerization;t he resulting reaction mixture likely contains paramagnetic species as judged by the broad signals observed by 1 HNMR spectroscopy.…”

Section: Resultsmentioning

confidence: 92%

“…Both 7 and 8 display well-resolved NMR spectra, suggesting that the closed-shell singlet state of the formally Fe 0 centre is not changed by the introduction of as econd metal such as rhodium. Particularly informative is the 13 CNMR chemical shift of the rhodium ligated carbene Catom, which exhibits ac haracteristic low field doublet (in 7: d C = 204.4 ppm, 1 J RhC = 42 Hz;i n8: d C = 185.5 ppm, 1 J RhC = 37.5 Hz). 15 NNMR chemical shifts for 6-8 suggest that the pyrazine ring retains aromaticity (d N (NMe) = 170.6 ppm in 6, 176.1 in 7,171.4 in 8,similar to 145.5 in [1]•I).…”

Section: Resultsmentioning

confidence: 99%

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A Redox‐Active Heterobimetallic N‐Heterocyclic Carbene Based on a Bis(imino)pyrazine Ligand Scaffold

et al. 2020

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An ew redox-active N-heterocyclic carbene (NHC) architecture is obtained using N-methylated pyrazinediimine iron complexes as precursors.The new species exhibit strong paccepting/s-donating properties and are able to ligate two metal centres simultaneously.T he redox activity was demonstrated by the reversible chemicalo xidation of ah eterobimetallic Fe 0 /Rh I example,w hich affords an isolable ligand-based radical cation. The reversible redox process was then applied in the catalytic hydrosilylation of 4,4'-difluorobenzophenone, where the reaction rate could be reversibly controlled as af unction of the catalyst oxidation state.T he new NHC exhibits high electrophilicity and nucleophilicity,w hich was demonstrated in the reversible activation of alcohols and amines.The electronic structure of the resulting complexes was investigated through various spectroscopic and computational methods.

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

A Redox‐Active Heterobimetallic N‐Heterocyclic Carbene Based on a Bis(imino)pyrazine Ligand Scaffold

et al. 2020

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“…Sowohl 7 als auch 8 weisen gutaufgelçste NMR-Spektren auf,was darauf hindeutet, dass der closed-shell Singulettzustand des formalen Fe 0 -Zentrums nicht durch die Einführung eines zweiten Metallzentrums, hier Rhodium, beeinflusst wird. Informativ ist die chemische Verschiebung des and das Rhodium gebundenen Carben-C-Atoms im 13 [1]•I). [18] Der Durchschnittswert der Rhodium-Carbonyl-Schwingungsfrequenzen (n av Rh-CO )w ird häufig zur Bestimmung der Gesamtdonorfähigkeit von NHCs genutzt.…”

Section: Ergebnisse Und Diskussionunclassified

“…[12] Formale reduktive Eliminierung von NHC-Derivaten aus sterischen Gründen ist ein literaturbekanntes Phänomen und im Falle von 3-5 ist vermutlich der sterische Anspruch der zugesetzten Base die Triebkraft hinter der Bildung des freien Carbens. [13] Es ist anzumerken, dass es während der Experimente zur Zersetzung der Verbindung 2 keine Hinweise füre ine Wanzlick-ähnliche Dimerisierung auftraten; die resultierende Reaktionsmischung enthält hçchstwahrscheinlich paramagnetische Verbindungen, erkennbar an den an den breiten Signalen der 1 H-NMR-Spektren.…”

Section: Introductionunclassified

Ein redoxaktives, heterobimetallisches N‐heterocyclisches Carben auf Basis eines Bis(imino)pyrazin‐Liganden

et al. 2020

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Ein neuartiger Vertreter der N-heterocyclischen Carbene (NHC) konnte ausgehend von einem N-methylierten Pyrazindiimin-Eisenkomplex dargestellt werden. Dieser zeichnet sich durchseine Fähigkeit als starker p-Akzeptor/s-Donor aus und ermçglicht die gleichzeitige Koordination zweier Metallzentren. Die Redoxaktivitätd es Systems konnte durch reversible chemische Oxidation einer heterobimetallischen Fe 0 / Rh I-Komplexverbindung gezeigt und das dabei entstehende ligandenzentrierte Radikalkation isoliert werden. In einem ersten Beispiel konnte dieser reversible Redoxprozess in der katalytischen Hydrosilylierung von 4,4'-Difluorobenzophenon angewandt werden. Hierbei konnte die Reaktionsgeschwindigkeit durch den Oxidationszustand des Katalysatorsystems reversibel moduliert werden. Das neue NHC agiert sowohl als starkes Elektrophil als auchals Nukleophil, was durchdie reversible Aktivierung von Alkoholen und Aminen gezeigt werden konnte.D ie elektronische Struktur der resultierenden Komplexew urdem ittels verschiedener spektroskopischer als auchquantenchemischer Methoden untersucht.

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“…19 Carbene-carboxylates have a distinct predisposition toward energy-relevant applications in CO2 reduction/conversion chemistry, and a number of reported studies have focused on functionalizing or selectively transferring the carboxylate motif. 10,[22][23][24][25][26][27][28][29][30] However, the ability of carbene-carboxylates to participate in direct electron transfer reactions with reducing metals (e.g. the alkali elements) is hitherto unknown.…”

Section: Introductionmentioning

confidence: 99%

Room Temperature Alkali Metal Reduction of Carbon Dioxide

La¹,

Ad²,

Hr³

et al. 2020

Preprint

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The reduction of the relatively inert carbon–oxygen bonds of CO2 to access useful CO2-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO2 and the MGE. Herein we report the first successful chemical reduction of CO2 at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO2 adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO2)]n(M = Li, Na, K, 2-4) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M2(CAAC–CO2)]n (5-8). It is notable that these crystalline clusters of reduced CO2 may also be isolated via the “one-pot” reaction of free CO2 with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products 2-8 were investigated using a combination of experimental and theoretical methods.

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Reductive Elimination at Carbon under Steric Control

Cited by 49 publications

References 41 publications

A Redox‐Active Heterobimetallic N‐Heterocyclic Carbene Based on a Bis(imino)pyrazine Ligand Scaffold

A Redox‐Active Heterobimetallic N‐Heterocyclic Carbene Based on a Bis(imino)pyrazine Ligand Scaffold

Ein redoxaktives, heterobimetallisches N‐heterocyclisches Carben auf Basis eines Bis(imino)pyrazin‐Liganden

Room Temperature Alkali Metal Reduction of Carbon Dioxide

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