Dual Character of Arduengo Carbene–Radical Adducts: Addition versus Coordination Product

Tumanskii, B. L.; Sheberla, Dennis; Molev, Gregory; Apeloig, Yitzhak

doi:10.1002/anie.200702297

Cited by 47 publications

(25 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has recently been established that much more reactive transient radicals are required for reactions with NHCs such as IMes. 23 Likewise, reaction mixtures of IMes and TEMPO in hexane solutions under a pressure of 5 atm of H 2 did not result in any reaction, as monitored by infrared spectroscopy.…”

Section: Scheme 2 Preparation Of Anhydrous Tempo-hmentioning

confidence: 90%

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres

et al. 2011

View full text Add to dashboard Cite

In this paper, we report a novel synthesis of anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-H). An X-ray crystal structure and full characterization of the compound are included. Compared to hydrated TEMPO-H, its anhydrous form exhibits improved stability and a differing chemical reactivity. The reactions of anhydrous TEMPO-H with a variety of low-valent carbon centres are described. For example, anhydrous TEMPO-H was reacted with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), an unsaturated NHC. Crystals of [CHNC 6 H 2 (CH 3 ) 3 ] 2 C ◊ ◊ ◊ HO-(NC 5 H 6 (CH 3 ) 4 ), IMes ◊ ◊ ◊ TEMPO-H, were isolated and a crystal structure determined. The experimental structure is compared to the results of theoretical calculations on the hydrogen-bonded dimer. Anhydrous TEMPO-H was also reacted with the saturated NHC, 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), giving the product [CH 2 Ni-Pr 2 C 6 H 3 ] 2 CH ◊ ◊ ◊ O(NC 5 H 6 (CH 3 ) 4 ). In contrast, the reaction of hydrated TEMPO-H with 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene gave small amounts of the hydrolysis product, N-(2,6-diisopropylphenyl)-N- [2-(2,6-diisopropylphenylamino)ethyl]formamide. Finally, anhydrous TEMPO-H was reacted with (triphenylphosphoranylidene)ketene to generate Ph 3 PC(H)C( O)O(NC 5 H 6 (CH 3 ) 4 ). A full characterization of the product, including an X-ray crystal structure, is described. Scheme 1 Structural isomers formed by the reaction of TEMPO-H (1) with NHCs (2).Access to anhydrous TEMPO-H has not been reported in the literature, but it was clear to us early on that the water in

show abstract

Section: Scheme 2 Preparation Of Anhydrous Tempo-hmentioning

confidence: 90%

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres

et al. 2011

View full text Add to dashboard Cite

show abstract

“…However, it was spectroscopically shown that NHC can stabilize a radical electron on the carbene carbon, as well of (NHC

^{^{.}}

)P(O)(O i Pr) 2 as of (NHC

^{^{.}}

)Re(CO) 5 2b. Such radical species were neither isolated nor structurally characterized due to their short life time 2b. In the case of the cyclic alkyl(amino) carbene (cAAC), one of the π‐donating N atoms in NHC is replaced by a σ‐donating quaternary C atom.…”

Section: Methodsmentioning

confidence: 99%

Synthesis and Characterization of a Triphenyl‐Substituted Radical and an Unprecedented Formation of a Carbene‐Functionalized Quinodimethane

Mondal

Samuel

Roesky

et al. 2014

Chemistry A European J

View full text Add to dashboard Cite

The trichlorosilylcarbene monoradical (Cy-cAAC ·)SiCl3 (1) was directly converted to (Cy-cAAC ·)SiPh3 (2) by substitution of the three chlorine atoms with phenyl groups without affecting the radical center adjacent to the silicon atom. In addition to the structure determination, compound 2 was studied by EPR spectroscopy and DFT calculations. The three hyperfine lines in the EPR spectrum of 2 are due to the coupling with (14)N nucleus. Functionalized 1,4-quinodimethane Me2-cAAC=C6H4=CPh2 (7) was isolated, whereas carbon analogue of radical 2 was targeted. Cyclic voltammogram of 7 indicated that a stable radical-anion 7 ·-, as well as a radical-cation 7 ·+, can be prepared. Theoretical calculations showed that one-electron ionization energy and electron affinity of 7 are 5.1 and 0.7 eV mol(-1), respectively.

show abstract

Section: Introductionmentioning

confidence: 99%

“…13 The phosphorus radical · P(O)(O i Pr) 2 was generated by the irradiation of {( i PrO) 2 (O)P} 2 Hg in the presence of free NHC (Figure 12). 13 Although the resulting carbene-diisopropylphosphoryl radical complex 17 · cannot be isolated, its half life is prolonged to 7.1 seconds. The EPR spectrum and calculations show that considerable electron density resides on the carbon (39%) and the remaining N 2 C 2 portion of the NHC (37%), while only a small portion is on the phosphorus atom (7.5%).…”

Section: Introductionmentioning

confidence: 99%

Carbene-stabilized main group radicals and radical ions

2013

View full text Add to dashboard Cite

Shortly after their discovery at the end of the 80s, stable singlet carbenes have been recognized as excellent ligands for transition metal based catalysts, and as organo-catalysts in their own right. At the end of the 2000s, it has been shown that they can coordinate main group elements in their zero oxidation state, and even activate small molecules. This review covers examples in the literature dealing with the most recent application of stable singlet carbenes, namely their use to stabilize radicals and radical ions that are otherwise unstable.

show abstract

Dual Character of Arduengo Carbene–Radical Adducts: Addition versus Coordination Product

Cited by 47 publications

References 18 publications

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres

Synthesis and Characterization of a Triphenyl‐Substituted Radical and an Unprecedented Formation of a Carbene‐Functionalized Quinodimethane

Carbene-stabilized main group radicals and radical ions

Contact Info

Product

Resources

About