Cyclic (alkyl)(amino)carbene (CAAC) ligands: Electronic structure and application as chemically- and redox-non-innocent ligands and chromophores

Breitwieser, Kevin; Munz, Dominik

doi:10.1016/bs.adomc.2022.03.003

Cited by 8 publications

(8 citation statements)

References 243 publications

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“…2 The non-innocent behavior of cAAC ligands in main group and transition metal complexes has been discussed in a number of computational and experimental studies. 5–9…”

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confidence: 99%

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

et al. 2023

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“…2 The non-innocent behavior of cAAC ligands in main group and transition metal complexes has been discussed in a number of computational and experimental studies. 5–9…”

mentioning

confidence: 99%

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

et al. 2023

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“…A similar mechanism has been proposed for the pre-activation of phosphine-based palladium catalysts . Furthermore, Ananikov et al showed that the dissociation of the NHC does not compromise the activity of the catalyst and that the presence of ureas might even boost turnover. , Cyclic (alkyl)(amino) carbenes (CAACs) stabilize low-valent compounds and radicals due to their π-acidity . Although not yet quantified, they are also expected to show a strong trans-effect.…”

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confidence: 81%

(CAAC)Pd(py) Catalysts Disproportionate to Pd(CAAC)₂

et al. 2023

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Palladium complexes with one N-heterocyclic carbene (NHC) and a pyridine ancillary ligand are powerful cross-coupling precatalysts. Herein, we report such complexes with a cyclic (alkyl)(amino)carbene (CAAC) ligand replacing the NHC. We find that the alleged reduced form, (CAAC)Pd(py), disproportionates to the (CAAC) 2 Pd 0 complex and palladium nanoparticles. This notwithstanding, they are potent catalysts in the Buchwald−Hartwig amination with aryl chlorides under mild conditions (60 °C). In the presence of dioxygen, these complexes catalyze the formation of diazenes from anilines. The catalytic activities of the NHC-and CAAC-supported palladium(0) and palladium(II) complexes are similar in the cross-coupling reaction, yet the CAAC complexes are superior for diazene formation.

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“…These cAAC ligands feature only a single nitrogen atom and exhibit much smaller HOMO–LUMO gaps due to the absence of aromaticity (Figure ). Consequently, metal–cAAC complexes can act as noninnocent ligands, and several carbene radical species have been reported …”

Section: Coordination Chemistry and Reactivitymentioning

confidence: 99%

“…Consequently, metal–cAAC complexes can act as noninnocent ligands, and several carbene radical species have been reported. 13 …”

Section: Coordination Chemistry and Reactivitymentioning

confidence: 99%

Carbene Radicals in Transition-Metal-Catalyzed Reactions

et al. 2023

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Discovered as organometallic curiosities in the 1970s, carbene radicals have become a staple in modern-day homogeneous catalysis. Carbene radicals exhibit nucleophilic radical-type reactivity orthogonal to classical electrophilic diamagnetic Fischer carbenes. Their successful catalytic application has led to the synthesis of a myriad of carbo- and heterocycles, ranging from simple cyclopropanes to more challenging eight-membered rings. The field has matured to employ densely functionalized chiral porphyrin-based platforms that exhibit high enantio-, regio-, and stereoselectivity. Thus far the focus has largely been on cobalt-based systems, but interest has been growing for the past few years to expand the application of carbene radicals to other transition metals. This Perspective covers the advances made since 2011 and gives an overview on the coordination chemistry, reactivity, and catalytic application of carbene radical species using transition metal complexes and catalysts.

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Cyclic (alkyl)(amino)carbene (CAAC) ligands: Electronic structure and application as chemically- and redox-non-innocent ligands and chromophores

Cited by 8 publications

References 243 publications

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

(CAAC)Pd(py) Catalysts Disproportionate to Pd(CAAC)₂

Carbene Radicals in Transition-Metal-Catalyzed Reactions

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Cyclic (alkyl)(amino)carbene (CAAC) ligands: Electronic structure and application as chemically- and redox-non-innocent ligands and chromophores

Cited by 8 publications

References 243 publications

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

Reply to the ‘Comment on “The oxidation state in low-valent beryllium and magnesium compounds”’ by S. Pan and G. Frenking,Chem. Sci., 2022,13, DOI: 10.1039/D2SC04231B

(CAAC)Pd(py) Catalysts Disproportionate to Pd(CAAC)2

Carbene Radicals in Transition-Metal-Catalyzed Reactions

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(CAAC)Pd(py) Catalysts Disproportionate to Pd(CAAC)₂