Mono- and Diaminocarbenes from Chloroiminium and -amidinium Salts:  Synthesis of Metal-Free Bis(dimethylamino)carbene

Otto, Michael; Conejero, Salvador; Canac, Yves; Romanenko, V. D.; Rudzevitch, Valentyn; Bertrand, Guy

doi:10.1021/ja0393325

Cited by 107 publications

(95 citation statements)

References 32 publications

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“…In addition, the deprotonation of cyclic six-membered formamidinium salts often leads to the isolation of alkali-metal adducts of the carbene as observed in the synthesis of 128 a. Bertrand et al developed a method for the preparation metal-free diaminocarbenes which is also suitable for the synthesis of cyclic diaminocarbenes of type 128. [229] In this synthesis 2-chloro-1,3-dimethyltetrahydropyrimidin-2-ium chloride is treated with bis(trimethylsilyl)mercury [230] resulting in dehalogenation of the N-heterocyclic ring to give the carbene 128 c (Scheme 64). In spite of the sterically less-demanding N-methyl substituents, carbene 128 c shows no tendency to dimerize.…”

Section: N-heterocyclic Carbenes Derived From Six-or Sevenmembered Hementioning

confidence: 99%

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

2008

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The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of beta-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

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Section: N-heterocyclic Carbenes Derived From Six-or Sevenmembered Hementioning

confidence: 99%

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

2008

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“…[20] -Treatment of chloro amidinium and azolium salts with bis(trimethylsilyl)mercury, providing elemental Hg, TMSCl, and the metal-free carbene (Scheme 2 e). [21] These 2-chloro azolium species can also be utilized for the formation of metal-NHC complexes by oxidative addition to the C À Cl bond. [22] In characterizing NHCs, the 13 C NMR chemical shift of the carbene carbon atom is quite diagnostic (Figure 2).…”

Section: Generation Of Free Nhcsmentioning

confidence: 99%

The Measure of All Rings—N‐Heterocyclic Carbenes

2010

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Quantification and variation of characteristic properties of different ligand classes is an exciting and rewarding research field. N-Heterocyclic carbenes (NHCs) are of special interest since their electron richness and structure provide a unique class of ligands and organocatalysts. Consequently, they have found widespread application as ligands in transition-metal catalysis and organometallic chemistry, and as organocatalysts in their own right. Herein we provide an overview on physicochemical data (electronics, sterics, bond strength) of NHCs that are essential for the design, application, and mechanistic understanding of NHCs in catalysis.

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“…[5] They are normally rapidly destroyed by moisture, [41] although they do not react with normal triplet oxygen, [42] and they can usually only be handled in hydrocarbon or ether solvents. [43] Bertrand et al [44] have recently reported a new general method which involves the reaction of chloroamidinium salts with Hg(SiMe 3 ) 2 ; some important results from this method will be discussed in Section 5. [43] Bertrand et al [44] have recently reported a new general method which involves the reaction of chloroamidinium salts with Hg(SiMe 3 ) 2 ; some important results from this method will be discussed in Section 5.…”

Section: Diaminocarbene Preparation; the Example Of Bis(diethylamino)mentioning

confidence: 99%

When and How Do Diaminocarbenes Dimerize?

et al. 2004

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No example of a simple uncatalyzed dimerization of a diaminocarbene has been clearly established, so it is timely to ask what factors control the thermodynamics of this reaction, and what mechanisms are responsible for the observed dimerizations? In agreement with qualitative experimental observations, the dimerizations of simple five- and six-membered-ring diaminocarbenes are calculated to be 100 kJ mol(-1) less favorable than those of acyclic counterparts. This large difference is semiquantitatively accounted for by bond and torsional angle changes around the carbene centers. Carbenes such as (Et(2)N)(2)C are kinetically stable in THF at 25 degrees C in agreement with calculated energy barriers, but they rapidly dimerize in the presence of the corresponding formamidinium ion. This proton-catalyzed process is probably the most common mechanism for dimer formation, and involves formation of C-protonated dimers, which can be observed in suitable cases. The possibility of alkali-metal-promoted dimerization is raised, and circumstantial evidence for this is presented.

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Mono- and Diaminocarbenes from Chloroiminium and -amidinium Salts: Synthesis of Metal-Free Bis(dimethylamino)carbene

Cited by 107 publications

References 32 publications

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

The Measure of All Rings—N‐Heterocyclic Carbenes

When and How Do Diaminocarbenes Dimerize?

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