Persistent carbene - Knowledge (XXG)

540: 3591: 426: 1431: 1172: 383: 2762: 619: 880: 3214: 3718: 596: 2925: 2572: 2360: 3420: 813: 178: 3164: 1032: 687: 265: 1043: 1509:. Whilst they have found that these ligands do not activate the metal catalyst as much as phosphine ligands they often result in more robust catalysts. Several catalytic systems have been looked into by Hermann and Enders, using catalysts containing imidazole and triazole carbene ligands, with moderate success. Grubbs has reported replacing a phosphine ligand (PCy 532: 3551: 654: 1126: 3306: 3733:. By way of example, a stable carbene prepared from potassium hydride can be filtered through a dry celite pad to remove excess KH (and resulting salts) from the reaction. On a relatively small scale, a suspension containing a stable carbene in solution can be allowed to settle and the supernatant solution pushed through a dried membrane 3468: 357: 629:-based carbenes are thermodynamically stable and have diagnostic C NMR chemical shift values between 210 and 220 ppm for the carbenic carbon. The X-ray structure of the triphenyl substituted carbene above shows an N–C–N bond angle of around 101°. The 5-methoxytriazole precursor to this carbene was made by the treatment of a 31: 288: 310: 481: 3495:

salt. Removing lithium ions resulting from deprotonation with reagents such as lithium diisopropylamide (LDA) can be especially problematic. Potassium and sodium salt by-products tend to precipitate from solution and can be removed. Lithium ions may be chemically removed by binding to species such as

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protection of the carbenic centre is limited especially when the N–C–X unit is part of a ring. These acyclic carbenes have diagnostic C NMR chemical shift values between 250 and 300 ppm for the carbenic carbon, further downfield than any other types of stable carbene. X-ray structures have shown

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Diaminocarbenes have diagnostic C NMR chemical shift values between 230 and 270 ppm for the carbenic atom. The X-ray structure of dihydroimidazole-2-ylidene shows a N–C–N bond angle of about 106°, whilst the angle of the acyclic carbene is 121°, both greater than those seen for imidazol-2-ylidenes.

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The preparation of stable carbenes free from metal cations has been keenly sought to allow further study of the carbene species in isolation from these metals. Separating a carbene from a carbene-metal complex can be problematic due to the stability of the complex. Accordingly, it is preferable to

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This carbene, the forerunner of a large family of carbenes with the imidazol-2-ylidene core, is indefinitely stable at room temperature in the absence of oxygen and moisture. It melts at 240–241 °C without decomposition. The C NMR spectrum shows a signal at 211 ppm for the carbenic atom. The

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as shown right can be an effective method of purification, although temperatures below 60 °C under high vacuum are preferable as these carbenes are relatively volatile and also could begin to decompose at these higher temperatures. Indeed, sublimation in some cases can give single crystals

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Unlike the aromatic imidazol-2-ylidenes or triazol-5-ylidenes, these carbenes appear not to be thermodynamically stable, as shown by the dimerisation of some unhindered cyclic and acyclic examples. Studies suggest that these carbenes dimerise via acid catalysed dimerisation (as in the

650:'s research group. In some of these compounds, the N–C–N unit is a member of a five- or six-membered non-aromatic ring, including a bicyclic example. In other examples, the adjacent nitrogens are connected only through the carbenic atom, and may or may not be part of separate rings. 933: 3411:

as strong bases has not been extensively studied, and have been unreliable for deprotonation of precursor salts. With non-aromatic salts, n-BuLi and PhLi can act as nucleophiles whilst t-BuLi can on occasion act as a source of hydride, reducing the salt with the generation of

698:. A thiazole based carbene (analogous to the carbene postulated by Breslow) has been prepared and characterised by X-ray crystallography. Other non-aromatic aminocarbenes with O, S and P atoms adjacent (i.e. alpha) to the carbene centre have been prepared, for example, 583:

Imidazole-based carbenes are thermodynamically stable and generally have diagnostic C NMR chemical shift values between 210 and 230 ppm for the carbenic carbon. Typically, X-ray structures of these molecules show N–C–N bond angles of 101–102°.

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In 2000, Bertrand obtained additional carbenes of the phosphanyl type, including (phosphanyl)(trifluoromethyl)carbene, stable in solution at -30 °C and a moderately stable (amino)(aryl)carbene with only one heteroatom adjacent to the carbenic atom.

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at −40 °C has been reported for imidazole-based carbenes. Arduengo and coworkers managed to prepare a dihydroimidazol-2-ylidene using NaH. However, this method has not been applied to the preparation of diaminocarbenes. In some cases,

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and coworkers in 1964, who presented evidence that the dimer did not dissociate; and by Winberg in 1965. However, subsequent experiments by Denk, Herrmann and others have confirmed this equilibrium, albeit in specific circumstances.

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Michael Otto; Salvador Conejero; Yves Canac; Vadim D. Romanenko; Valentyn Rudzevitch; Guy Bertrand (2004). "Mono- and Diaminocarbenes from Chloroiminium and -amidinium Salts: Synthesis of Metal-Free Bis(dimethylamino)carbene".

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backbone. The following year, the first acyclic persistent carbene demonstrated that stability did not even require a cyclic backbone. Unhindered derivatives of the hydrogenated and acyclic carbenes dimerized, suggesting that

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H. W. Wanzlick; H. J. Schonherr (1970). "Chemie nucleophiler Carbene, XVIII, 1) 1.3.4.5-Tetraphenyl-imidazoliumperchlorat" [Chemistry of nucleophilic carbenes, XVIII. 1) 1,3,4,5-Tetraphenylimidazolium perchlorate].

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Roger W. Alder; Michael E. Blake; Simone Bufali; Craig P. Butts; A. Guy Orpen; Jan Schütz; Stuart J. Williams (2001). "Preparation of tetraalkylformamidinium salts and related species as precursors to stable carbenes".

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salts, a protonated precursor species. Accordingly, this reaction can be acid catalysed. This reaction occurs because unlike imidazolium based carbenes, there is no loss of aromaticity in protonation of the carbene.

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There exist several variants of the stable carbenes above where one of the nitrogen atoms adjacent to the carbene center (the α nitrogens) has been replaced by an alternative heteroatom, such as oxygen, sulfur, or

3371:. However, these catalysts have proved ineffective for the preparation of non-imidazolium adducts as they tend to act as nucleophiles towards the precursor salts and in so doing are destroyed. The presence of 3574:

Vacuum pyrolysis, with the removal of neutral volatile byproducts i.e. methanol or chloroform, has been used to prepare dihydroimidazole and triazole based carbenes. Historically the removal of chloroform by

1001:-heterocyclic carbenes (rNHC). A variety of free carbenes can be isolated and are stable at room temperature. Other free carbenes are not stable and are susceptible to intermolecular decomposition pathways. 645:

The two families above can be seen as special cases of a broader class of compounds which have a carbenic atom bridging two nitrogen atoms. A range of such diaminocarbenes have been prepared principally by

993:-heterocyclic carbenes (NHCs) except that canonical resonance structures with the carbene depicted cannot be drawn without adding additional charges. Mesoionic carbenes are also referred to as abnormal 1107:

nature of these carbenes, which is lost upon dimerisation. In fact imidazol-2-ylidenes are so thermodynamically stable that only in highly constrained conditions are these carbenes forced to dimerise.

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M. Scholl; T. M. Trnka; J. P. Morgan; R. H. Grubbs (1999). "Increased ring closing metathesis activity of ruthenium-based olefin metathesis catalysts coordinated with imidazolin-2-ylidene ligands".

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make the carbene free from these metals in the first place. Indeed, some metal ions, rather than stabilising the carbene, have been implicated in the catalytic dimerisation of unhindered examples.

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CHPh, and noted increased ring closing metathesis as well as exhibiting "a remarkable air and water stability". Molecules containing two and three carbene moieties have been prepared as potential

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atoms adjacent to the carbene centre, and so are able to coordinate to even relatively electron deficient metals. Enders and Hermann have shown that these carbenes are suitable replacements for

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Wolf Janine; Böhlmann Winfried; Findeisen Matthias; Gelbrich Thomas; Hofmann Hans-Jorg; Schulze Borbel (2007). "Reply to "Recently Reported Crystalline Isothiazole Carbenes: Myth or Reality"".

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Itoh, T; Nakata, Y; Hirai, K; Tomioka, H (2006). "Triplet Diphenylcarbenes Protected by Trifluoromethyl and Bromine Groups. A Triplet Carbene Surviving a Day in Solution at Room Temperature".

637:. This may indicate that these carbenes are less aromatic than imidazol-2-ylidenes, as the imidazolium precursors do not react with nucleophiles due to the resultant loss of aromaticity. 5904:

D. Enders; H. Gielen; G. Raabe; J. Runsink; J. H. Teles (1996). "Synthesis and Stereochemistry of the First Chiral (Imidazolinylidene)- and (Triazolinylidene)palladium(II) Complexes".

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Solé, Stéphane; Gornitzka, Heinz; Schoeller, Wolfgang W.; Bourissou, Didier; Bertrand, Guy (2001). "(Amino)(Aryl)Carbenes: Stable Singlet Carbenes Featuring a Spectator Substituent".

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works very cleanly for the deprotonation of all types of salts, except for unhindered formamidinium salts, where this base can act as a nucleophile to give a triaminomethane adduct.

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through loss of methanol from 2-methoxytriazoles. Only a limited range of these molecules have been reported, with the triphenyl substituted molecule being commercially available.

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R. W. Alder; M. E. Blake; C. Bortolotti; S. Buffali; C. P. Butts; E. Lineham; J. M. Oliva; A. G. Orpen; M. J. Quayle (1999). "Complexation of stable carbenes with alkali metals".

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was used by Wanzlick in his early attempts to prepare dihydroimidazol-2-ylidenes but this method is not widely used. The Enders laboratory has used vacuum pyrolysis of adduct

3535:, is insoluble in the solvent. The elevated temperatures suggest that this method is not suitable for the preparation of unstable dimerising carbenes. A single example of the 3185:

Upon coordination to metal centers, the C carbene resonance usually shifts highfield, depending on the Lewis acidity of the complex fragment. Based on this observation, Huynh

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Carbene Chemistry: From Fleeting Intermediates to Powerful Reagents, (Chapter 4, Hideo Tomioka (triplet state); Chapter 5 (singlet state), Roger W. Alder) - ed. Guy Bertrand

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Depending on the arrangement of the three nitrogen atoms in triazol-5-ylidene, there are two possible isomers, namely 1,2,3-triazol-5-ylidenes and 1,2,4-triazol-5-ylidenes.

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and the trifluoromethyl groups on the phenyl rings, that shield the carbene and prevent or slow down the process of dimerization to a 1,1,2,2-tetra(phenyl)alkene. Based on

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Christophe Buron; Heinz Gornitzka; Vadim Romanenko; Guy Bertrand (2000). "Stable Versions of Transient Push-Pull Carbenes: Extending Lifetimes from Nanoseconds to Weeks".

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Those carbenes that have been isolated to date tend to be colorless solids with low melting points. These carbenes tend to sublime at low temperatures under high vacuum.

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In the modern understanding, the superficially unoccupied p-orbital on a (meta)stable carbene is not, in fact, fully empty. Instead, the carbene Lewis structures are in

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D. Enders; K. Breuer; G. Raabe; J. Runsink; J. H. Teles; J. P. Melder; K. Ebel; S. Brode (1995). "Preparation, Structure, and Reactivity of 1,3,4-Triphenyl-4,5-dihydro-1

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used to make the lithium amide. Titration of lithium amide can be used to determine the amount of hydroxide in solution. The deprotonation of precursor salts with metal

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These compounds were called "push-pull carbenes" in reference to the contrasting electron affinities of the phosphorus and silicon atoms. They exhibit both carbenic and

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being deprotonated. The major drawback with this method of preparation is the problem of isolation of the free carbene from the metals ions used in their preparation.

1392:) probably proceed via deprotonation, resulting in the generation of a nucleophile (XR) which can attack the generated salt giving the impression of a H–X insertion. 469:. Indeed, most persistent carbenes are stabilized by two flanking nitrogen centers. The outliers include an aminothiocarbene and an aminooxycarbene, which use other 3193:-palladium(II)-carbene complexes. The use of a C-labeled N-heterocyclic carbene ligand also allows for the study of mixed carbene-phosphine complexes, which undergo 4405:

A. J. Arduengo; F. Davidson; H. V. R. Dias; J. R. Goerlich; D. Khasnis; W. J. Marshall; T. K. Prakasha (1997). "An Air Stable Carbene and Mixed Carbene "Dimers"".

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have performed a range of organic reactions involving a triazol-5-ylidene. These reactions are outlined below and may be considered as a model for other carbenes.

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values for the conjugate acids of several NHC families have been examined in aqueous solution. pKa values of triazolium ions lie in the range 16.5–17.8, around 3 p

473:, and room-temperature-stable bis(diisopropylamino)cyclopropenylidene, in which the carbene atom is connected to two carbon atoms in a three-member, aromatic, 1546: 299:

reactivity. An X-ray structure of this molecule has not been obtained and at the time of publication some doubt remained as to their exact carbenic nature.

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ImC: might be exceptional, rather than paradigmatic. But the behavior of the acyclic carbenes offered a tantalizing clue to the stabilization mechanism.

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However, further work showed that diaminocarbenes will deprotonate the DMSO solvent, with the resulting anion reacting with the resulting amidinium salt.

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Several bases and reaction conditions have been employed with varying success. The degree of success has been principally dependent on the nature of the

65:), but does not exhibit the tremendous instability typically associated with such moieties. The best-known examples and by far largest subgroup are the 453:

Unlike the cyclic derivatives, acyclic carbenes are flexible and bonds to the carbenic atom admit rotation. But bond rotation in the compound appeared

5524:

Higgins, Eleanor M.; Sherwood, Jennifer A.; Lindsay, Anita G.; Armstrong, James; Massey, Richard S.; Alder, Roger W.; O'Donoghue, Annmarie C. (2011).

99:. Excitation to a carbene structure then accounts for the carbene-like dimerization that some persistent carbenes undergo over the course of days. 1219: 785:. However, these compounds seem to exhibit some alkynic properties, and when published the exact carbenic nature of these red oils was in debate. 509:

ring, with the hydrogen in carbon 2 of the ring (between the two nitrogen atoms) removed, and other hydrogens replaced by various groups. These

5759:

DeHope, A; Lavallo, V; Donnadieu, B; Schoeller, WW; Bertrand, G (2007). "Recently reported crystalline isothiazole carbenes: Myth or reality".

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for cross-coupling reactions. NHC-metal complexes, specifically Ag(I)-NHC complexes have been widely tested for their biological applications.

5483:"Proton Transfer Reactions of Triazol-3-ylidenes: Kinetic Acidities and Carbon Acid pKaValues for Twenty Triazolium Salts in Aqueous Solution" 4338:

Tapu, Daniela; Dixon, David A.; Roe, Christopher (12 August 2009). "13C NMR Spectroscopy of "Arduengo-type" Carbenes and Their Derivatives".

3729:. However, provided rigorously dry, relatively non-acidic and air-free materials are used, stable carbenes are reasonably robust to handling 4987:

W. A. Herrmann; C. Kocher; L. J. Goossen; G. R. J. Artus (1996). "Heterocyclic Carbenes: A High-Yielding Synthesis of Novel, Functionalized

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A considerable range of imidazol-2-ylidenes have been synthesised, including those in which the 1,3-positions have been functionalised with

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atoms for the two hydrogens at ring positions 4 and 5 yielded the first air-stable carbene. Its extra stability probably results from the

5026:-Heterocyclic Carbenes: Generation under Mild Conditions and Formation of Group 8–10 Transition Metal Complexes Relevant to Catalysis". 3325:

salts. The acyclic carbenes and the tetrahydropyrimidinyl based carbenes were prepared by deprotonation using strong homogeneous bases.

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of elements gives some idea of the complexes which have been prepared, and in many cases these have been identified by single crystal

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In particular, the formal substitution of sulfur for one of the nitrogens in imidazole would yield the aromatic heterocyclic compound

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Díez-González, Silvia; Marion, Nicolas; Nolan, Steven P. (2009-08-12). "N-Heterocyclic Carbenes in Late Transition Metal Catalysis".

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Imidazol-2-ylidenes, triazol-5-ylidenes (and less so, diaminocarbenes) have been shown to coordinate to a plethora of elements, from

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Reactive Intermediate Chemistry By Robert A. Moss, Matthew Platz, Maitland Jones (Chapter 8, Stable Singlet Carbenes, Guy Bertrand)

5976:; Lukas J. Goossen; Christian Köcher; Georg R. J. Artus (1996). "Chiral Heterocylic Carbenes in Asymmetric Homogeneous Catalysis". 4733:

Alder, RW; Chaker, L; Paolini, FP (2004). "Bis(diethylamino)carbene and the mechanism of dimerisation for simple diaminocarbenes".

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to give imidazol-2-ylidenes or diaminocarbenes has not been widely used. The method was used to prepare dihydroimidazole carbenes.

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by-products and excess hydride being removed by filtration. In practice this reaction is often too slow, requiring the addition of

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Although the figure below shows the two parts of the molecule in one flat plane, molecular geometry puts the two aromatic parts in

539: 3118: 250: 5653:

Enders, D.; Breuer, K.; Runsink, J.; Teles, J.H. (1996). "Chemical Reactions of the Stable Carbene 1,3,4-Triphenyl-4,5-dihydro-1

1099:. However, imidazol-2-ylidenes and triazol-5-ylidenes are thermodynamically stable and do not dimerise, and have been stored in 6384: 837:

core, a three-carbon ring with a double bond between the two atoms adjacent to the carbenic one. This family is exemplified by

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Wolf, J; Böhlmann, W; Findeisen, M; Gelbrich, T; Hofmann, HJ; Schulze, B (2007). "Synthesis of stable isothiazole carbenes".

838: 419: 6159:

Garrison Jered C.; Youngs Wiley J. (2005). "Ag(I) N-Heterocyclic Carbene Complexes: Synthesis, Structure, and Application".

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Tomioka, H; Iwamoto, E; Itakura, H; Hirai, K (2001). "Generation and characterization of a fairly stable triplet carbene".

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Hans-Werner Wanzlick; E. Schikora (1960). "Ein neuer Zugang zur Carben-Chemie" [A new way into carbene chemistry].

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Gernot Boche; Christof Hilf; Klaus Harms; Michael Marsch; John C. W. Lohrenz (1995). "Crystal Structure of the Dimeric (4-

3738: 3441: 817: 245:, proposed that these imidazole-based carbenes should be more stable than their 4,5-dihydro analogues, due to Hückel-type 3947: 3344:

would be the ideal base for deprotonating these precursor salts. The hydride should react irreversibly with the loss of

6034:"13C NMR Spectroscopic Determination of Ligand Donor Strengths Using N-Heterocyclic Carbene Complexes of Palladium(II)" 3142:. The reactions that such carbenes participate in are very different from those in which organic carbenes participate. 185:

This exchange was proposed to proceed via intermediacy of a thiazol-2-ylidene. In 2012 the isolation of the so-called

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the respective diimidazolium salt. Only the deprotonation of the doubly tethered diimidazolium salt with the shorter

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A. J. Arduengo; H. V. R. Dias; R. L. Harlow; M. Kline (1992). "Electronic stabilization of nucleophilic carbenes".

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Persistent triplet state carbenes are likely to have very similar reactivity as other non-persistent triplet state

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The first air-stable ylidic carbene, a chlorinated member of the imidazol-2-ylidene family, was obtained in 1997.

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G. Bertrand; A. Igau; A. Baceiredo; G. Trinquier (1989). "trimethylsilylcarbene: A Stable Nucleophilic Carbene".

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One of the more useful physical properties is the diagnostic chemical shift of the carbenic carbon atom in the C-

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of stable carbenes can be difficult, due to the unavailability of suitable non-acidic polar solvents. Air-free

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Alder, Roger W.; Blake, Michael E.; Chaker, Leila; Harvey, Jeremy N.; Paolini, François; Schütz, Jan (2004).

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Denk M. K.; Hatano K.; Ma M. (1999). "Nucleophilic Carbenes and the Wanzlick Equilibrium A Reinvestigation".

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spectrum. Typically this peak is in the range between 200 and 300 ppm, where few other peaks appear in the C-

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spectrum. An example is shown on the left for a cyclic diaminocarbene which has a carbenic peak at 238 ppm.

3139: 1164:) have been shown to dimerise, albeit quite slowly. This has been presumed to be due to the high barrier to 953: 6332:

Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. (2014). "An Overview of N-Heterocyclic Carbenes".

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R. W. Alder; M. E. Blake; J. M. Oliva (1999). "Diaminocarbenes; Calculation of Barriers to Rotation about C

3908:-Heterocyclic Carbenes: Generation and Reactivity of the Elusive 2,2-Diamino Enols (Breslow Intermediates)" 3846:

Ronald Breslow (1958). "On the Mechanism of Thiamine Action. IV.1 Evidence from Studies on Model Systems".

3367:, which increase the rate of reaction of this heterogeneous system, via the generation of tert-butoxide or 862: 1420: 895: 337:

in the ring of the carbene than in the parent imidazolium compound, indicating that there was very little

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Arduengo, Anthony J.; Harlow, Richard L.; Kline, Michael (January 1991). "A stable crystalline carbene".

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For a review on the physico-chemical properties (electronics, sterics, ...) of N-heterocyclic carbenes:

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M. K. Denk; A. Thadani; K. Hatano; A. J. Lough (1997). "Steric Stabilization of Nucleophilic Carbenes".

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of carbene precursor salts with strong bases has proved a reliable route to almost all stable carbenes:

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R. W. Alder, in 'Diaminocarbenes: exploring structure and reactivity', ed. G. Bertrand, New York, 2002

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A. J. Arduengo, J. R. Goerlich and W. J. Marshall (1997). "A Stable Thiazol-2-ylidene and Its Dimer".

4244:-bis-carbenoid, triply bonded species: synthesis of a stable λ-phosphino carbene-λ-phosphaacetylene". 3291:

Several approaches have been developed in order to prepare stable carbenes, these are outlined below.

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interactions would have a significant destabilising effect. To avoid this electronic interaction, the

6343: 5973: 5935: 5826: 5342: 4938: 4824: 4489: 4444: 4057:

D. M. Lemal; R. A. Lovald; K. I. Kawano (1964). "Tetraaminoethylenes. The Question of Dissociation".

3969: 3781: 1589: 1578: 1175:"Least motion" (path A – not allowed) and "non-least motion" (path B) routes of carbene dimerisation. 1100: 1096: 858: 663: 438: 221: 193: 171: 143: 3590: 762: 725:

Carbenes that formally derive from imidazole-2-ylidenes by substitution of sulfur, oxygen, or other

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are still the most stable and the most well studied and understood family of persistent carbenes.

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D. Kovacs; M. S. Lee; D. Olson; J. E. Jackson (1996). "Carbene-to-Carbene Oxygen Atom Transfer".

6184: 6141: 5938:; Martina Elison; Jakob Fischer; Christian Köcher; Georg R. J. Artus (1995). "Metal Complexes of 5851: 5659: 5565: 5366: 4861: 4183: 3805: 3726: 3353: 3266: 3135: 3125: 1452: 1349: 1025: 913:

Again the figure below is not an adequate representation of the actual molecular structure: both

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H. W. Wanzlick; E. Schikora (1960). "Ein nucleophiles Carben" [A nucleophilic carbene].

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on the carbenic carbon would be forced into close proximity. Presumably the resulting repulsive

703: 4923:

Lavallo, Vincent; Canac, Yves; Donnadieu, Bruno; Schoeller, Wolfgang W.; Bertrand, Guy (2006).

3444:) generally work well for the deprotonation of all types of salts, providing that not too much 769:. Thus it is possible that the reverse of this process might be occurring in similar carbenes. 425: 6464: 6438: 6359: 6308: 6292: 6263: 6176: 6133: 6125: 6091: 6071: 6006: 5777: 5738: 5635: 5557: 5506: 5490: 5435: 5419: 5358: 5313: 5287: 5220: 5189: 5158: 5059: 4964: 4929: 4894: 4746: 4626: 4593: 4505: 4480: 4460: 4435: 4407: 4376: 4356: 4312: 4279: 4246: 4211: 4159: 4115: 4087: 4059: 3930: 3876: 3848: 3797: 3631: 3532: 3445: 3341: 2467: 1514: 1357: 1092: 986: 981: 604: 580:

Molecules containing two and even three imidazol-2-ylidene groups have also been synthesised.

330: 254: 213: 5942:-Heterocyclic Carbenes – A New Structural Principle for Catalysts in Homogeneous Catalysis". 3737:. Stable carbenes are readily soluble in non-polar solvents such as hexane, and so typically 3547:

derived carbene to give the tetramethyldiaminocarbene and fluorenone has also been reported:

690:

Synthesised heteroamino carbenes (top and bottom right) and Bertrand's carbenes (bottom left)

158:

ring exchanges a hydrogen atom (attached to carbon 2 of the ring) for a furfural residue. In

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Stable carbenes are very reactive, and so the minimum amount of handling is desirable using

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Berkessel A.; Elfert S.; Yatham V. R.; Neudörfl J.-M.; Schlörer N. E.; Teles J. H. (2012).

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Shown right is an X-ray structure showing a complex between a diaminocarbene and potassium

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Stable carbenes readily coordinate to metals; in this case a diaminocarbene coordinates to

1218: 237:

In 1970, Wanzlick's group generated imidazol-2-ylidene carbenes by the deprotonation of an

6038: 5694: 4925:"Cyclopropenylidenes: From Interstellar Space to an Isolated Derivative in the Laboratory" 3559: 3516: 3391: 1626: 1621: 1616: 1611: 1606: 1601: 1596: 1476: 806: 733:α-nitrogens are expected to be unstable, as they have the potential to dissociate into an 630: 618: 6228:

N. Kuhn; T. Kratz (1993). "Synthesis of Imidazol-2-ylidenes by Reduction of Imidazole-2(3

5692:-1,2,4-triazol-5-ylidene – applications of a stable carbene in synthesis and catalysis". 4661:

R. W. Alder; P. R. Allen; M. Murray; A. G. Orpen (1996). "Bis(diisopropylamino)carbene".

4523:

Lai Chun-Liang; Guo Wen-Hsin; Lee Ming-Tsung; Hu Ching-Han (2005). "Ligand properties of

3284:

In these cases, strong unhindered nucleophiles are avoided whether they are generated in

968:

of 158.8°. The planes of the phenyl groups are almost at right angles to each other (the

6347: 5346: 4942: 4892:

R. W. Alder; C. P. Butts; A. G. Orpen (1998). "Stable Aminooxy- and Aminothiocarbenes".

4828: 4493: 4448: 3973: 3785: 5385: 5308: 5278: 5218:

H. D. Hartzler (1972). "1,3-Dithiolium carbenes from acetylenes and carbon disulfide".

4959: 4924: 3823: 3734: 3449: 3258: 3226: 1569: 1468: 969: 926: 892: 608: 546: 485: 387: 258: 242: 225: 124: 6018: 5071: 4127: 4085:

H. E. Winberg; J. E. Carnahan; D. D. Coffman; M. Brown (1965). "Tetraaminoethylenes".

3213: 1203:("non-least motion"). Carbene dimerisation can be catalyzed by both acids and metals. 6453: 6145: 5569: 5541: 5458: 5133: 5028: 4993: 4783: 4541: 4291: 3702: 3536: 3492: 3424: 3408: 3368: 3299: 3278: 3189:

developed a new methodology to determine ligand donor strengths by C NMR analysis of

2591: 1539: 1491: 1448: 1385: 1365: 1192: 1188: 1180: 1165: 1138: 1111: 1055: 948:. As with the other carbenes, this species contains large bulky substituents, namely 850: 303: 79:

Modern theoretical analysis suggests that the term "persistent carbene" is in fact a

6188: 5855: 5688:

Enders, D.; Breuer, K.; Teles, J.H.; Ebel, K. (1997). "1,3,4-Triphenyl-4,5-dihydro-1

5456:

R. W. Alder; P. R. Allen; S. J. Williams (1995). "Stable carbenes as strong bases".

4559: 3717: 1031: 940:

Exposure to oxygen (a triplet diradical) converts this carbene to the corresponding

879: 686: 6420:

T. Dröge; F. Glorius (2010). "The Measure of All Rings - N-Heterocyclic Carbenes".

5370: 3961: 3357: 3274: 3202: 2955: 2792: 2657: 1651: 1584: 1337: 1063: 1042: 941: 899: 738: 128: 84: 83:. Persistent carbenes do not in fact have a carbene electronic structure in their 6371: 5873:-Butylthiazolato)(glyme)lithium: Carbene Character of a Formyl Anion Equivalent". 4501: 3826:(1957). "Mechanism of Thiamine Action: Participation of a Thiazolium Zwitterion". 3809: 595: 531: 6067: 4456: 3766:

Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. (2014). "An Overview of

1179:

Diaminocarbenes do not truly dimerise, but rather form the dimer by reaction via

102:

Persistent carbenes in general, and Arduengo carbenes in particular, are popular

4555: 4310:

Arduengo, A.J.; Harlow, R.L.; Kline, M. (1991). "A stable crystalline carbene".

3501: 3375:

ions as an impurity in the metal hydride could also destroy non-aromatic salts.

3318: 3065: 3043: 3032: 2723: 2679: 2668: 1646: 1460: 1396: 957: 821: 647: 634: 470: 458: 372: 338: 334: 246: 238: 159: 92: 5403: 4624:

J. Arduengo; J. R. Goerlich; W. J. Marshall (1995). "A stable diaminocarbene".

3550: 3531:. A contributing factor to the success of this reaction is that the byproduct, 3419: 1195:

carbenes do not approach head to head ("least motion"), but rather the carbene

653: 497:

The following are examples of the classes of stable carbenes isolated to date:

386:

1,3,4,5-tetramethylimidazol-2-ylidene, a relatively unhindered carbene. (

17: 6109: 5906: 5671: 4873: 4340: 4000: 3828: 3329: 3163: 2869: 2847: 2814: 2734: 2646: 2613: 2580: 2200: 2189: 1874: 1534: 1211:

The chemistry of stable carbenes has not been fully explored. However, Enders

965: 918: 873: 812: 778: 680: 466: 209: 177: 155: 136: 58: 6129: 5918: 5706: 5040: 5005: 4195: 4012: 3981: 3746:

suitable for X-ray analysis. However, strong complexation to metal ions like

4950: 4141:

Böhm Volker P. W.; Herrmann Wolfgang A. (2000). "The Wanzlick Equilibrium".

3627: 3563: 3524: 3413: 3383: 3372: 3349: 3305: 3230: 3021: 2999: 2988: 2977: 2913: 2803: 2770: 2745: 2712: 2701: 2299: 2233: 2211: 2167: 2143: 2070: 1993: 1925: 1852: 1838: 1740: 1671: 1661: 1656: 1530: 1499: 1484: 1464: 1200: 1196: 1134: 1035:

Measurement of the pKa value for the conjugate acid of an imidazol-2-ylidene

961: 903: 888: 866: 765:

carbenes (i.e. where X = X = S), which then dimerise to give derivatives of

758: 726: 570: 506: 442: 399: 6442: 6434: 6407: 6363: 6312: 6180: 6137: 5990: 5956: 5887: 5847: 5809: 5781: 5773: 5742: 5734: 5639: 5630: 5612: 5597: 5561: 5510: 5439: 5362: 5317: 5260: 5110: 4968: 4750: 4712: 4675: 4509: 4464: 4360: 4163: 4043: 3934: 3925: 3903: 3801: 611:

ring are pictured below and were first prepared by Enders and coworkers by

543:

1,3-Dimesityl-4,5-dichloroimidazol-2-ylidene, the first air-stable carbene.

264: 5022:

W. A. Herrmann; M. Elison; J. Fischer; C. Kocher; G. R. J. Artus (1996). "

4813:–N Bonds, Barriers to Dimerization, Proton Affinities, and C NMR Shifts". 4156:

10.1002/1521-3773(20001117)39:22<4036::AID-ANIE4036>3.0.CO;2-L

3507:

Metal free carbenes have been prepared in several ways as outlined below:

249:. Wanzlick did not however isolate imidazol-2-ylidenes, but instead their 6247: 5482: 5467: 4240:

A. Igau; H. Grutzmacher; A. Baceiredo; G. Bertrand (1988). "Analogous α,α

3706: 3544: 3520: 3497: 3364: 3345: 3152: 3076: 2933: 2836: 2825: 2690: 2551: 2522: 2511: 2478: 2445: 2401: 2390: 2368: 2288: 2132: 2092: 1982: 1971: 1960: 1949: 1896: 1798: 1776: 1697: 1495: 1104: 1103:

in the absence of water and air for years. This is presumably due to the

1058:

gave 90% of the 2-substituted adduct, with only 10% of the corresponding

907: 816:

In the second step of this reaction sequence the proton is abstracted by

798: 777:

In Bertrand's persistent carbenes, the unsaturated carbon is bonded to a

714: 695: 626: 562: 554: 394:

Early workers attributed the stability of Arduengo carbenes to the bulky

167: 151: 80: 6355: 5232: 5201: 5170: 4638: 4605: 4388: 4324: 4277:

G. Bertrand; R. Reed (1994). "λ-Phosphinocarbenes λ-phosphaacetylenes".

4258: 4223: 4099: 4071: 3888: 3860: 3793: 3288:

or are present as an impurity in other reagents (such as LiOH in BuLi).

484:

Stable carbenes with oxygen or sulfur atoms bound to the carbenic atom (

5553: 5057:

H. V. R. Dias; W. C. Jin (1994). "A stable tridentate carbene ligand".

3747: 3623: 3387: 3270: 3054: 2966: 2944: 2902: 2880: 2858: 2635: 2624: 2602: 2500: 2434: 2412: 2379: 2339: 2255: 2222: 2178: 2156: 2114: 2103: 2081: 2059: 1936: 1863: 1729: 1666: 1502: 1142: 1125: 1047: 949: 782: 376: 280:. These species can be represented as either a λ-phosphinocarbene or λ- 62: 6304: 6275: 6172: 6121: 6052: 6033: 5502: 5431: 5299: 4906: 4836: 4419: 4352: 309: 287: 6214: 5354: 5142: 4792: 4742: 3379: 3262: 3222: 3010: 2891: 2781: 2562: 2423: 2350: 2310: 2266: 2244: 2037: 2026: 2015: 1885: 1827: 1787: 1765: 1711: 1488: 1480: 1407:) was questioned. The researchers were only able to isolate 2-imino-2 1059: 914: 883:

Delocalization in a stable triplet carbene reported by Tomioka (2001)

734: 718: 710: 411: 296: 212:. They conjectured that the carbene existed in equilibrium with its 163: 147: 103: 4029:

H. W. Wanzlick (1962). "Aspects of Nucleophilic Carbene Chemistry".

3467: 1156:

N–C–SR) and non-aromatic carbenes such as diaminocarbenes (such as R

5156:

R. Breslow (1957). "Rapid Deuterium Exchange in Thiazolium Salts".

4209:

R. Gleiter; R. Hoffmann (1968). "Stabilizing a singlet methylene".

3874:

R. Breslow (1957). "Rapid Deuterium Exchange in Thiazolium Salts".

356: 4527:-heterocyclic and Bertrand carbenes: A density functional study". 3716: 3589: 3549: 3472: 3466: 3418: 3304: 3212: 2533: 2321: 1907: 1754: 1429: 1217: 1170: 1124: 1041: 1030: 960:

of the divalent carbon atom to its neighbors is claimed to be 138

931: 878: 811: 802: 685: 652: 617: 594: 538: 530: 517: 480: 479: 462: 424: 381: 355: 308: 286: 263: 176: 88: 34: 1475:. Stable carbenes are believed to behave in a similar fashion to 706:

based carbenes have been characterised by X-ray crystallography.

302:

In 1991, Arduengo and coworkers crystallized a diaminocarbene by

3540: 3314: 3261:

of an imidazol-2-ylidene was measured at ca. 24) and react with

2489: 2456: 2048: 2004: 1809: 936:

A persistent triplet carbene (right), synthesized by Itoh (2006)

887:

In 2006 a triplet carbene was reported by the same group with a

521: 429:

Bis(diisopropylamino) carbene, the first acyclic stable carbene.

30: 5187:

H. D. Haztzler (1970). "Nucleophilic 1,3-dithiolium carbenes".

944:. The diphenylmethane compound is formed when it is trapped by 3528: 3254: 3179: 3175: 2277: 1110:

Chen and Taton made a doubly tethered diimidazol-2-ylidene by

1015: 291:

Alkyne and carbene resonances structures of Bertrand's carbene

3705:

decomposition of a diazomethane product via the expulsion of

853:, dimerizing when forced into triplet states. Nevertheless, 414:

groups also affords 1,3,4,5-tetramethylimidazol-2‑ylidene (Me

3317:, have been prepared by the deprotonation of the respective 5583:

T. A. Taton; P. Chen (1996). "A Stable Tetraazafulvalene".

3948:

Chemists Approach Elusive Breslow Intermediate Carmen Drahl

3138:

carbenes; in which carbenes are tethered to a metal and an

433:

In 1995, Arduengo's group obtained a carbene derivative of

6393:

M. Regitz (1996). "Stable Carbenes—Illusion or Reality?".

5283:-Heterocyclic Carbenes with Tunable Electronic Properties" 3128:

carbenes in which carbenes are tethered to a metal and an

505:

The first stable carbenes to be isolated were based on an

4777:-piperidyl)carbene and its slow dimerisation to tetrakis( 3515:

Another approach of preparing carbenes has relied on the

3399:

can be employed without the addition of a metal hydride.

3313:

Imidazol-2-ylidenes and dihydroimidazol-2-ylidenes, such

3309:

Deprotonation of precursor salts to give stable carbenes.

921:

with respect to each other. The carbene carbon has an sp-

3701:

Persistent triplet state carbenes have been prepared by

1091:

At one time, stable carbenes were thought to reversibly

722:

N–C–X bond angles of around 104° and 109° respectively.

181:

Deuterium exchange of the C2-proton of thiazolium salt.

5899: 5897: 1062:, indicating that these molecules are also reasonably 6088:

N-Heterocyclic carbenes in transition metal catalysis

196:

and coworkers conjectured that carbenes derived from

76:), in which nitrogen atoms flank the formal carbene. 3109:

Carbenes in organometallic chemistry & catalysis

406:

the carbene from dimerising. But replacement of the

1133:If this dimer existed as a dicarbene, the electron 861:

to produce a comparatively stable triplet carbene (

797:-heterocyclic carbene has a structure analogous to 1483:are said to be good σ-donors through the carbenic 1479:in their coordination properties to metals. These 1148:On the other hand, heteroamino carbenes (such as R 809:. This results in a planar six-electron compound. 268:Preparation and trapping of an imidazol-2-ylidene. 27:Type of carbene demonstrating particular stability 5096:-1,2,4-triazol-5-ylidene, a New Stable Carbene". 3630:salts to give a metal-free carbene and elemental 3277:addition, other non-aromatic salts are not (i.e. 1083:units more acidic than related imidazolium ions. 1014:The imidazol-2-ylidenes are strong bases, having 929:each conjugating with one of the aromatic rings. 4175: 4173: 3709:gas, at a wavelength of 300 nm in benzene. 524:, alkyloxy, alkylamino, alkylphosphino and even 465:on adjacent nitrogen atoms while preserving the 437:, proving that stability did not arise from the 5272: 5270: 5213: 5211: 5182: 5180: 4918: 4916: 5754: 5752: 5683: 5681: 5277:Präsang, C; Donnadieu, B; Bertrand, G (2005). 5087: 5085: 5083: 5081: 3265:. Clearly these reactions are performed using 1129:Dimerisation of tethered diimidazol-2-ylidenes 1050:as an NMR solvent can have unexpected results. 657:Synthesised cyclic and acyclic diaminocarbenes 4728: 4726: 4724: 4722: 4560:"What's in a name? Carbenes: a reality check" 3594:Preparation of carbenes via vacuum pyrolysis. 3491:was used as a strong base to deprotonate the 1554: 1403:) derived from an isothiazolium perchlorate ( 1325:Dimethylacetylene dicarboxylate, THF, reflux 891:of 40 minutes. This carbene is prepared by a 142:(thiamine), was the catalyst involved in the 8: 5821: 5819: 4854: 4852: 4850: 4848: 4846: 4619: 4617: 4615: 4586: 4584: 4582: 4580: 4400: 4398: 4305: 4303: 4301: 4272: 4270: 4268: 4235: 4233: 3229:chemistry. One practical application is the 35:1,3-Dimesityl-imidazol-4,5-dihydro-2-ylidene 5968: 5966: 5930: 5928: 5613:"When and How Do Diaminocarbenes Dimerize?" 5279:"Stable Planar Six-π-Electron Six-Membered 4991:-Heterocyclic Carbenes in Liquid Ammonia". 4024: 4022: 3993: 3991: 3554:Preparation of carbenes by dechalcogenation 3273:. Although imidazolium salts are stable to 3103: No carbene complex with element known 547:View the 3D structure with external viewer. 5017: 5015: 4982: 4980: 4978: 1561: 1547: 1024: ≈ 24 for the conjugate acid in 761:derivatives is proposed to give transient 633:with sodium methoxide, which attacks as a 6051: 5629: 5451: 5449: 5307: 5126: 5124: 5122: 5120: 4958: 4887: 4885: 4883: 4804: 4802: 4768: 4766: 4764: 4762: 4760: 4656: 4654: 4652: 4650: 4648: 3924: 849:Persistent carbenes tend to exist in the 833:Another family of carbenes is based on a 5052: 5050: 4693: 4691: 4689: 4687: 4685: 3750:will in most cases prevent sublimation. 3162: 3095: Carbene complex with element known 1232:3,6-diphenyl-1,2,4,5-tetrazine, toluene 1222: 997:-heterocyclic carbenes (aNHC) or remote 29: 3758: 2587: 1487:, but poor π-acceptors due to internal 839:bis(diisopropylamino)cyclopropenylidene 352:Stabilization through adjacent orbitals 204:of the corresponding 2-trichloromethyl 4773:R. W. Alder; M. E. Blake (1997). "Bis( 3487:. This complex was formed when excess 3348:to give the desired carbene, with the 3269:, avoiding compounds of even moderate 2951: 2788: 2653: 876:positions with respect to each other. 3217:A second generation Grubbs' catalyst. 3061: 3039: 3028: 2719: 2675: 2664: 1054:Reaction of imidazol-2-ylidenes with 865:) in 2001. It has an unusually long 622:Examples of 1,2,4-triazol-5-ylidenes. 37:, a representative persistent carbene 7: 6068:N-Heterocyclic carbenes in synthesis 6032:Han Vinh Huynh; et al. (2009). 2865: 2843: 2810: 2730: 2642: 2609: 2576: 2196: 2185: 1513:) with an imidazol-2-ylidene in the 1122:–) resulted in the dicarbene dimer: 224:. This conjecture was challenged by 166:was found to rapidly exchange for a 3017: 2995: 2984: 2973: 2909: 2799: 2766: 2741: 2708: 2697: 2295: 2229: 2207: 2163: 2139: 2066: 1989: 1870: 1848: 1834: 1736: 1427:is no longer considered as stable. 1336:These carbenes tend to behave in a 906:light in benzene with expulsion of 553:In particular, substitution of two 3363:. These reagents generate soluble 3119:transition metal carbene complexes 3072: 2929: 2832: 2821: 2686: 2547: 2518: 2507: 2474: 2441: 2386: 2364: 2284: 2128: 2088: 1978: 1956: 1945: 1921: 1892: 127:proposed that a relatively stable 25: 5384:Michael Freemantle (2001-08-13). 3587:to generate a triazol-5-ylidene. 3340:One might believe that sodium or 3050: 2940: 2898: 2876: 2854: 2631: 2620: 2598: 2496: 2463: 2430: 2408: 2397: 2375: 2335: 2251: 2218: 2174: 2110: 2099: 2077: 2055: 1967: 1932: 1859: 1794: 1772: 1725: 1693: 1243:2 equiv., PhNCO, toluene, reflux 925:, the two remaining orthogonal p- 6327:Reviews on persistent carbenes: 5537:-heterocyclic carbenes in water" 4542:10.1016/j.jorganchem.2005.07.058 3006: 2962: 2923: 2887: 2777: 2760: 2570: 2558: 2419: 2358: 2346: 2262: 2240: 2152: 2033: 2022: 2011: 1823: 1707: 233:Isolation of persistent carbenes 5391:Chemical & Engineering News 5386:"Triplet Carbene has Long Life" 3386:hydride in a mixture of liquid 3147:Triplet state carbene chemistry 2529: 2317: 2306: 1903: 1881: 1783: 1761: 1224:Reactions of triazol-5-ylidene 569:on the carbon atom bearing the 565:substituents, which reduce the 461:character that would place the 324:-diadamantyl-imidazol-2-ylidene 154:. In this cycle, the vitamin's 6206:J. Chem. Soc., Perkin Trans. 1 3680: 3463:Metal-free carbene preparation 3113:Carbenes can be stabilised as 2485: 2452: 2044: 2000: 1805: 1750: 333:structure revealed longer N–C 1: 6019:10.1016/S0040-4039(99)00217-8 5072:10.1016/S0040-4039(00)76219-8 4502:10.1126/science.292.5523.1901 4128:10.1016/S0040-4039(99)00164-1 3442:tetramethylpiperidide (LiTMP) 2273: 1269:, toluene, or PhNCS, THF, RT 375:toward adjacent lone-pair or 5829:; Christian Köcher (1997). " 5533:s of the conjugate acids of 4457:10.1126/science.288.5467.834 4292:10.1016/0010-8545(94)03005-B 3427:salts with tert-butyllithium 1438:) was proved to be unstable. 1010:Basicity and nucleophilicity 577:through the sigma-backbone. 5657:-1,2,4-triazol-5-ylidene". 3697:Photochemical decomposition 1388:. The insertion reactions ( 1187:Unlike the dimerisation of 789:Other nucleophilic carbenes 208:compounds with the loss of 6491: 5404:10.1021/cen-v079n033.p011a 3604:Bis(trimethylsilyl)mercury 3599:Bis(trimethylsilyl)mercury 3201:-isomerization due to the 3130:electron-withdrawing group 3121:fall into two categories: 2754: 1845: 1747: 1704: 1683: 1670: 1665: 1660: 1655: 1650: 1645: 1640: 1635: 1630: 1625: 1620: 1615: 1610: 1605: 1600: 1595: 1588: 1583: 1577: 1542: 979: 824:groups shield the carbene. 757:) with electron deficient 599:Triazol-5-ylidene isomers. 535:Stable imidazol-2-ylidenes 493:Classes of stable carbenes 341:character to these bonds. 306:of an imidazolium cation: 241:salt. Wanzlick as well as 220:derivative, the so-called 5833:-Heterocyclic Carbenes". 5672:10.1002/jlac.199619961212 5481:Massey Richard S (2012). 4874:10.1002/jlac.199719970213 3770:-Heterocyclic Carbenes". 3721:Sublimation of a carbene. 3562:of thioureas with molten 2922: 2759: 1288:, or Se, toluene, reflux 1199:attacks the empty carbon 435:dihydroimidazol-2-ylidene 198:dihydroimidazol-2-ylidene 6470:Organometallic chemistry 5919:10.1002/cber.19961291213 5707:10.1002/prac.19973390170 5041:10.1002/chem.19960020708 5006:10.1002/chem.19960021222 4196:10.1002/jlac.19707310121 4013:10.1002/cber.19610940905 3982:10.1002/ange.19600721409 3436:Lithium amides like the 3249:NHCs are often strongly 3221:NHCs are widely used as 772: 420:thermodynamically stable 108:organometallic chemistry 72:(NHC) (sometimes called 4951:10.1126/science.1126675 4735:Chemical Communications 3397:potassium tert-butoxide 3239:NHC-Palladium Complexes 3140:electron-donating group 1419:was proposed through a 859:electron delocalization 410:-adamantyl groups with 363:of the allylic system. 57:has a carbon atom with 6435:10.1002/anie.201001865 6408:10.1002/anie.199106741 5991:10.1002/anie.199628051 5957:10.1002/anie.199523711 5888:10.1002/anie.199504871 5848:10.1002/anie.199721621 5810:10.1002/anie.200702746 5774:10.1002/anie.200702272 5735:10.1002/anie.200604305 5631:10.1002/anie.200400654 5598:10.1002/anie.199610111 5261:10.1002/anie.198906211 5111:10.1002/anie.199510211 4713:10.1002/anie.199726071 4676:10.1002/anie.199611211 4564:Chemistry with a Twist 4044:10.1002/anie.196200751 3926:10.1002/anie.201205878 3722: 3595: 3555: 3476: 3438:diisopropylamide (LDA) 3428: 3310: 3218: 3168: 1439: 1421:rearrangement reaction 1333: 1176: 1130: 1095:through the so-called 1051: 1036: 989:(MICs) are similar to 937: 902:precursor by 300 884: 845:Triplet state carbenes 825: 691: 658: 623: 600: 550: 536: 489: 430: 391: 364: 325: 292: 276:and others isolated a 269: 251:coordination compounds 182: 70:-heterocyclic carbenes 38: 6423:Angew. Chem. Int. Ed. 6396:Angew. Chem. Int. Ed. 6066:S. P. Nolan (2006). 5979:Angew. Chem. Int. Ed. 5945:Angew. Chem. Int. Ed. 5876:Angew. Chem. Int. Ed. 5836:Angew. Chem. Int. Ed. 5798:Angew. Chem. Int. Ed. 5762:Angew. Chem. Int. Ed. 5723:Angew. Chem. Int. Ed. 5618:Angew. Chem. Int. Ed. 5586:Angew. Chem. Int. Ed. 5249:Angew. Chem. Int. Ed. 5099:Angew. Chem. Int. Ed. 4701:Angew. Chem. Int. Ed. 4664:Angew. Chem. Int. Ed. 4144:Angew. Chem. Int. Ed. 4032:Angew. Chem. Int. Ed. 3913:Angew. Chem. Int. Ed. 3720: 3593: 3553: 3470: 3457:hexamethyldisilazides 3422: 3308: 3216: 3167:Carbene peak in C NMR 3166: 3132:(usually a carbonyl), 1473:X-ray crystallography 1434:Isothiazole carbene ( 1433: 1221: 1174: 1128: 1045: 1034: 935: 917:rings are positioned 882: 863:bis(9-anthryl)carbene 815: 737:(RC≡CR) and a carbon 689: 656: 641:Other diaminocarbenes 621: 598: 542: 534: 483: 428: 385: 359: 312: 290: 267: 180: 33: 6248:10.1055/s-1993-25902 5985:(23–24): 2805–2807. 5974:Wolfgang A. Herrmann 5936:Wolfgang A. Herrmann 5827:Wolfgang A. Herrmann 5468:10.1039/c39950001267 4781:-piperidyl)ethene". 4536:(24–25): 5867–5875. 1572:: Persistent carbene 1443:Carbene complexation 1415:). The intermediate 1395:The reported stable 1384:) as well as simple 1380:), cycloadditions ( 1097:Wanzlick equilibrium 954:computer simulations 857:and associates used 674:Heteroamino carbenes 664:Wanzlick equilibrium 559:electron-withdrawing 402:substituents, which 222:Wanzlick equilibrium 194:Hans-Werner Wanzlick 187:Breslow intermediate 144:benzoin condensation 6356:10.1038/nature13384 6348:2014Natur.510..485H 6086:F. Glorius (2007) 5497:(50): 20421–20432. 5347:2001Natur.412..626T 5294:(29): 10182–10183. 5233:10.1021/ja00794a039 5202:10.1021/ja00708a058 5171:10.1021/ja01564a064 4943:2006Sci...312..722L 4901:(44): 11526–11527. 4829:1999JPCA..10311200A 4823:(50): 11200–11211. 4639:10.1021/ja00149a034 4633:(44): 11027–11028. 4606:10.1021/ja00040a007 4530:J. Organomet. Chem. 4494:2001Sci...292.1901S 4488:(5523): 1901–1903. 4449:2000Sci...288..834B 4414:(52): 12742–12749. 4389:10.1021/ja00001a054 4325:10.1021/ja00001a054 4259:10.1021/ja00227a028 4224:10.1021/ja01022a023 4100:10.1021/ja01087a040 4072:10.1021/ja01066a044 3974:1960AngCh..72..494W 3919:(49): 12370–12374. 3889:10.1021/ja01564a064 3861:10.1021/ja01547a064 3794:10.1038/nature13384 3786:2014Natur.510..485H 3727:air-free techniques 3622:reacts with chloro- 3378:Deprotonation with 3336:Metal hydride bases 3267:air-free techniques 3245:Preparation methods 3159:Physical properties 1453:main group elements 1350:insertion reactions 1299:Maleimide, THF, RT 1225: 1005:Chemical properties 946:cyclohexa-1,4-diene 829:Cyclopropenylidenes 805:atom replaced by a 773:Bertrand's carbenes 511:imidazol-2-ylidenes 501:Imidazol-2-ylidenes 55:resonance structure 5660:Liebigs Ann. Chem. 5554:10.1039/C0CC03367G 4862:Liebigs Ann. Chem. 4184:Liebigs Ann. Chem. 3723: 3596: 3556: 3477: 3475:to form a complex. 3448:is present in the 3429: 3323:dihydroimidazolium 3311: 3219: 3169: 1440: 1358:addition reactions 1334: 1223: 1177: 1131: 1052: 1037: 1026:dimethyl sulfoxide 987:Mesoionic carbenes 976:Mesoionic carbenes 938: 885: 835:cyclopropenylidene 826: 745:Non-amino carbenes 692: 659: 624: 605:triazol-5-ylidenes 601: 588:Triazol-5-ylidenes 551: 537: 490: 475:cyclopropenylidene 441:of the conjugated 431: 392: 365: 326: 293: 270: 218:tetraaminoethylene 183: 93:aromatic resonance 43:persistent carbene 39: 6475:Organic compounds 6460:Functional groups 6429:(39): 6940–6952. 6342:(7506): 485–496. 6305:10.1021/ja0393325 6293:J. Am. Chem. Soc. 6276:10.1021/ja961324j 6270:(34): 8144–8145. 6264:J. Am. Chem. Soc. 6209:(14): 1586–1593. 6173:10.1021/cr050004s 6167:(11): 3978–4008. 6122:10.1021/cr900074m 6053:10.1021/om900667d 6046:(18): 5395–5404. 6013:(12): 2247–2250. 6007:Tetrahedron Lett. 5951:(21): 2371–2374. 5913:(12): 1483–1488. 5842:(20): 2162–2187. 5768:(36): 6922–6925. 5729:(17): 3118–3121. 5666:(12): 2019–2028. 5624:(44): 5896–5911. 5503:10.1021/ja308420c 5491:J. Am. Chem. Soc. 5432:10.1021/ja056575j 5420:J. Am. Chem. Soc. 5341:(6847): 626–628. 5300:10.1021/ja052987g 5288:J. Am. Chem. Soc. 5227:(13): 4379–4387. 5221:J. Am. Chem. Soc. 5190:J. Am. Chem. Soc. 5159:J. Am. Chem. Soc. 5060:Tetrahedron Lett. 5000:(12): 1627–1636. 4937:(5774): 722–724. 4907:10.1021/ja9819312 4895:J. Am. Chem. Soc. 4837:10.1021/jp9934228 4787:(16): 1513–1514. 4737:(19): 2172–2173. 4707:(23): 2607–2609. 4670:(10): 1121–1123. 4627:J. Am. Chem. Soc. 4600:(14): 5530–5534. 4594:J. Am. Chem. Soc. 4443:(5467): 834–836. 4420:10.1021/ja973241o 4408:J. Am. Chem. Soc. 4377:J. Am. Chem. Soc. 4353:10.1021/cr800521g 4313:J. Am. Chem. Soc. 4280:Coord. Chem. Rev. 4253:(19): 6463–6466. 4247:J. Am. Chem. Soc. 4218:(20): 5457–5460. 4212:J. Am. Chem. Soc. 4150:(22): 4036–4038. 4122:(11): 2057–2060. 4116:Tetrahedron Lett. 4088:J. Am. Chem. Soc. 4066:(12): 2518–2519. 4060:J. Am. Chem. Soc. 3877:J. Am. Chem. Soc. 3855:(14): 3719–3726. 3849:J. Am. Chem. Soc. 3780:(7506): 485–496. 3739:recrystallisation 3533:potassium sulfide 3342:potassium hydride 3085: 3084: 1537:carbene ligands. 1515:olefin metathesis 1457:transition metals 1332: 1331: 982:Mesoionic carbene 200:were produced by 170:in a statistical 133:thiazol-2-ylidene 87:, but instead an 74:Arduengo carbenes 16:(Redirected from 6482: 6446: 6411: 6375: 6317: 6316: 6299:(4): 1016–1017. 6286: 6280: 6279: 6258: 6252: 6251: 6225: 6219: 6218: 6215:10.1039/b104110j 6199: 6193: 6192: 6156: 6150: 6149: 6116:(8): 3612–3676. 6104: 6098: 6084: 6078: 6064: 6058: 6057: 6055: 6029: 6023: 6022: 6001: 5995: 5994: 5970: 5961: 5960: 5932: 5923: 5922: 5901: 5892: 5891: 5866: 5860: 5859: 5823: 5814: 5813: 5792: 5786: 5785: 5756: 5747: 5746: 5717: 5711: 5710: 5685: 5676: 5675: 5650: 5644: 5643: 5633: 5608: 5602: 5601: 5592:(9): 1011–1013. 5580: 5574: 5573: 5548:(5): 1559–1561. 5521: 5515: 5514: 5487: 5478: 5472: 5471: 5453: 5444: 5443: 5414: 5408: 5407: 5381: 5375: 5374: 5355:10.1038/35088038 5328: 5322: 5321: 5311: 5274: 5265: 5264: 5243: 5237: 5236: 5215: 5206: 5205: 5196:(5): 1412–1413. 5184: 5175: 5174: 5165:(7): 1762–1763. 5153: 5147: 5146: 5143:10.1039/a808951e 5128: 5115: 5114: 5105:(9): 1021–1023. 5089: 5076: 5075: 5066:(9): 1365–1366. 5054: 5045: 5044: 5019: 5010: 5009: 4984: 4973: 4972: 4962: 4920: 4911: 4910: 4889: 4878: 4877: 4856: 4841: 4840: 4816:J. Phys. Chem. A 4806: 4797: 4796: 4793:10.1039/a703610h 4770: 4755: 4754: 4743:10.1039/b409112d 4730: 4717: 4716: 4695: 4680: 4679: 4658: 4643: 4642: 4621: 4610: 4609: 4588: 4575: 4574: 4572: 4570: 4552: 4546: 4545: 4520: 4514: 4513: 4475: 4469: 4468: 4430: 4424: 4423: 4402: 4393: 4392: 4371: 4365: 4364: 4347:(8): 3385–3407. 4335: 4329: 4328: 4307: 4296: 4295: 4274: 4263: 4262: 4243: 4237: 4228: 4227: 4206: 4200: 4199: 4177: 4168: 4167: 4138: 4132: 4131: 4110: 4104: 4103: 4094:(9): 2055–2056. 4082: 4076: 4075: 4054: 4048: 4047: 4026: 4017: 4016: 4007:(9): 2389–2393. 3995: 3986: 3985: 3956: 3950: 3945: 3939: 3938: 3928: 3899: 3893: 3892: 3883:(7): 1762–1763. 3871: 3865: 3864: 3843: 3837: 3836: 3820: 3814: 3813: 3763: 3682: 3669: 3668: 3667: 3577:vacuum pyrolysis 3570:Vacuum pyrolysis 3511:Dechalcogenation 3235:Grubbs' catalyst 3223:ancillary ligand 3104: 3102: 3096: 3094: 3081: 3079: 3070: 3068: 3059: 3057: 3048: 3046: 3037: 3035: 3026: 3024: 3015: 3013: 3004: 3002: 2993: 2991: 2982: 2980: 2971: 2969: 2960: 2958: 2949: 2947: 2938: 2936: 2927: 2926: 2918: 2916: 2907: 2905: 2896: 2894: 2885: 2883: 2874: 2872: 2863: 2861: 2852: 2850: 2841: 2839: 2830: 2828: 2819: 2817: 2808: 2806: 2797: 2795: 2786: 2784: 2775: 2773: 2764: 2763: 2750: 2748: 2739: 2737: 2728: 2726: 2717: 2715: 2706: 2704: 2695: 2693: 2684: 2682: 2673: 2671: 2662: 2660: 2651: 2649: 2640: 2638: 2629: 2627: 2618: 2616: 2607: 2605: 2596: 2594: 2585: 2583: 2574: 2573: 2567: 2565: 2556: 2554: 2538: 2536: 2527: 2525: 2516: 2514: 2505: 2503: 2494: 2492: 2483: 2481: 2472: 2470: 2461: 2459: 2450: 2448: 2439: 2437: 2428: 2426: 2417: 2415: 2406: 2404: 2395: 2393: 2384: 2382: 2373: 2371: 2362: 2361: 2355: 2353: 2344: 2342: 2326: 2324: 2315: 2313: 2304: 2302: 2293: 2291: 2282: 2280: 2271: 2269: 2260: 2258: 2249: 2247: 2238: 2236: 2227: 2225: 2216: 2214: 2205: 2203: 2194: 2192: 2183: 2181: 2172: 2170: 2161: 2159: 2148: 2146: 2137: 2135: 2119: 2117: 2108: 2106: 2097: 2095: 2086: 2084: 2075: 2073: 2064: 2062: 2053: 2051: 2042: 2040: 2031: 2029: 2020: 2018: 2009: 2007: 1998: 1996: 1987: 1985: 1976: 1974: 1965: 1963: 1954: 1952: 1941: 1939: 1930: 1928: 1912: 1910: 1901: 1899: 1890: 1888: 1879: 1877: 1868: 1866: 1857: 1855: 1843: 1841: 1832: 1830: 1814: 1812: 1803: 1801: 1792: 1790: 1781: 1779: 1770: 1768: 1759: 1757: 1745: 1743: 1734: 1732: 1716: 1714: 1702: 1700: 1563: 1556: 1549: 1540: 1507:catalytic cycles 1477:organophosphines 1314:CH=CHR, THF, RT 1226: 1191:carbenes, these 1145:units dimerise. 1116:methylene bridge 820:, while the two 767:tetrathiafulvene 751:carbon disulfide 749:The reaction of 613:vacuum pyrolysis 567:electron density 422:unhindered NHC. 322: 282:phosphaacetylene 278:phosphinocarbene 206:dihydroimidazole 202:vacuum pyrolysis 160:deuterated water 97:steric shielding 59:incomplete octet 51:organic molecule 21: 6490: 6489: 6485: 6484: 6483: 6481: 6480: 6479: 6450: 6449: 6419: 6392: 6331: 6325: 6323:Further reading 6320: 6288: 6287: 6283: 6260: 6259: 6255: 6227: 6226: 6222: 6201: 6200: 6196: 6158: 6157: 6153: 6106: 6105: 6101: 6085: 6081: 6065: 6061: 6039:Organometallics 6031: 6030: 6026: 6003: 6002: 5998: 5972: 5971: 5964: 5934: 5933: 5926: 5903: 5902: 5895: 5868: 5867: 5863: 5825: 5824: 5817: 5794: 5793: 5789: 5758: 5757: 5750: 5719: 5718: 5714: 5695:J. Prakt. Chem. 5687: 5686: 5679: 5652: 5651: 5647: 5610: 5609: 5605: 5582: 5581: 5577: 5532: 5523: 5522: 5518: 5485: 5480: 5479: 5475: 5455: 5454: 5447: 5416: 5415: 5411: 5383: 5382: 5378: 5330: 5329: 5325: 5276: 5275: 5268: 5245: 5244: 5240: 5217: 5216: 5209: 5186: 5185: 5178: 5155: 5154: 5150: 5130: 5129: 5118: 5091: 5090: 5079: 5056: 5055: 5048: 5021: 5020: 5013: 4986: 4985: 4976: 4922: 4921: 4914: 4891: 4890: 4881: 4858: 4857: 4844: 4812: 4808: 4807: 4800: 4772: 4771: 4758: 4732: 4731: 4720: 4697: 4696: 4683: 4660: 4659: 4646: 4623: 4622: 4613: 4590: 4589: 4578: 4568: 4566: 4558:(11 Sep 2016). 4554: 4553: 4549: 4522: 4521: 4517: 4477: 4476: 4472: 4432: 4431: 4427: 4404: 4403: 4396: 4373: 4372: 4368: 4337: 4336: 4332: 4309: 4308: 4299: 4276: 4275: 4266: 4241: 4239: 4238: 4231: 4208: 4207: 4203: 4179: 4178: 4171: 4140: 4139: 4135: 4112: 4111: 4107: 4084: 4083: 4079: 4056: 4055: 4051: 4028: 4027: 4020: 3997: 3996: 3989: 3958: 3957: 3953: 3946: 3942: 3901: 3900: 3896: 3873: 3872: 3868: 3845: 3844: 3840: 3822: 3821: 3817: 3765: 3764: 3760: 3756: 3715: 3699: 3691: 3687: 3683: 3677: 3673: 3666: 3663: 3662: 3661: 3659: 3657: 3653: 3649: 3645: 3641: 3634:. For example: 3621: 3617: 3613: 3609: 3601: 3572: 3560:desulfurisation 3517:desulfurisation 3513: 3465: 3434: 3405: 3338: 3297: 3247: 3211: 3161: 3149: 3117:species. These 3111: 3100: 3099: 3092: 3091: 3077: 3075: 3074: 3066: 3064: 3063: 3055: 3053: 3052: 3044: 3042: 3041: 3033: 3031: 3030: 3022: 3020: 3019: 3011: 3009: 3008: 3000: 2998: 2997: 2989: 2987: 2986: 2978: 2976: 2975: 2967: 2965: 2964: 2956: 2954: 2953: 2945: 2943: 2942: 2934: 2932: 2931: 2924: 2914: 2912: 2911: 2903: 2901: 2900: 2892: 2890: 2889: 2881: 2879: 2878: 2870: 2868: 2867: 2859: 2857: 2856: 2848: 2846: 2845: 2837: 2835: 2834: 2826: 2824: 2823: 2815: 2813: 2812: 2804: 2802: 2801: 2793: 2791: 2790: 2782: 2780: 2779: 2771: 2769: 2768: 2761: 2755: 2746: 2744: 2743: 2735: 2733: 2732: 2724: 2722: 2721: 2713: 2711: 2710: 2702: 2700: 2699: 2691: 2689: 2688: 2680: 2678: 2677: 2669: 2667: 2666: 2658: 2656: 2655: 2647: 2645: 2644: 2636: 2634: 2633: 2625: 2623: 2622: 2614: 2612: 2611: 2603: 2601: 2600: 2592: 2590: 2589: 2581: 2579: 2578: 2571: 2563: 2561: 2560: 2552: 2550: 2549: 2534: 2532: 2531: 2523: 2521: 2520: 2512: 2510: 2509: 2501: 2499: 2498: 2490: 2488: 2487: 2479: 2477: 2476: 2468: 2466: 2465: 2457: 2455: 2454: 2446: 2444: 2443: 2435: 2433: 2432: 2424: 2422: 2421: 2413: 2411: 2410: 2402: 2400: 2399: 2391: 2389: 2388: 2380: 2378: 2377: 2369: 2367: 2366: 2359: 2351: 2349: 2348: 2340: 2338: 2337: 2322: 2320: 2319: 2311: 2309: 2308: 2300: 2298: 2297: 2289: 2287: 2286: 2278: 2276: 2275: 2267: 2265: 2264: 2256: 2254: 2253: 2245: 2243: 2242: 2234: 2232: 2231: 2223: 2221: 2220: 2212: 2210: 2209: 2201: 2199: 2198: 2190: 2188: 2187: 2179: 2177: 2176: 2168: 2166: 2165: 2157: 2155: 2154: 2144: 2142: 2141: 2133: 2131: 2130: 2115: 2113: 2112: 2104: 2102: 2101: 2093: 2091: 2090: 2082: 2080: 2079: 2071: 2069: 2068: 2060: 2058: 2057: 2049: 2047: 2046: 2038: 2036: 2035: 2027: 2025: 2024: 2016: 2014: 2013: 2005: 2003: 2002: 1994: 1992: 1991: 1983: 1981: 1980: 1972: 1970: 1969: 1961: 1959: 1958: 1950: 1948: 1947: 1937: 1935: 1934: 1926: 1924: 1923: 1908: 1906: 1905: 1897: 1895: 1894: 1886: 1884: 1883: 1875: 1873: 1872: 1864: 1862: 1861: 1853: 1851: 1850: 1846: 1839: 1837: 1836: 1828: 1826: 1825: 1810: 1808: 1807: 1799: 1797: 1796: 1788: 1786: 1785: 1777: 1775: 1774: 1766: 1764: 1763: 1755: 1753: 1752: 1748: 1741: 1739: 1738: 1730: 1728: 1727: 1712: 1710: 1709: 1705: 1698: 1696: 1695: 1684: 1573: 1567: 1528: 1524: 1520: 1512: 1445: 1313: 1287: 1283: 1268: 1209: 1163: 1159: 1155: 1151: 1121: 1089: 1082: 1075: 1022: 1012: 1007: 984: 978: 869:of 19 minutes. 847: 831: 807:methylene group 791: 775: 756: 747: 713:and sulfur are 676: 643: 631:triazolium salt 590: 544: 503: 495: 463:positive charge 457:, suggesting a 449: 417: 354: 320: 313:Preparation of 235: 140: 121: 116: 45:(also known as 28: 23: 22: 18:Stable carbenes 15: 12: 11: 5: 6488: 6486: 6478: 6477: 6472: 6467: 6462: 6452: 6451: 6448: 6447: 6413: 6412: 6402:(6): 674–676. 6390: 6387: 6382: 6377: 6324: 6321: 6319: 6318: 6281: 6253: 6242:(6): 561–562. 6220: 6194: 6151: 6099: 6079: 6059: 6024: 5996: 5962: 5924: 5893: 5882:(4): 487–489. 5861: 5815: 5787: 5748: 5712: 5677: 5645: 5603: 5575: 5530: 5516: 5473: 5445: 5426:(3): 957–967. 5409: 5376: 5323: 5266: 5255:(5): 621–622. 5238: 5207: 5176: 5148: 5137:(3): 241–242. 5116: 5077: 5046: 5035:(7): 772–780. 5011: 4974: 4912: 4879: 4868:(2): 365–374. 4842: 4810: 4798: 4756: 4718: 4681: 4644: 4611: 4576: 4547: 4515: 4470: 4425: 4394: 4383:(1): 361–363. 4366: 4330: 4319:(1): 361–363. 4297: 4264: 4229: 4201: 4169: 4133: 4105: 4077: 4049: 4018: 3987: 3951: 3940: 3894: 3866: 3838: 3824:Ronald Breslow 3815: 3757: 3755: 3752: 3735:syringe filter 3714: 3711: 3698: 3695: 3694: 3693: 3689: 3685: 3679: 3675: 3671: 3664: 3655: 3651: 3647: 3643: 3639: 3619: 3615: 3611: 3607: 3600: 3597: 3571: 3568: 3512: 3509: 3464: 3461: 3433: 3430: 3404: 3401: 3337: 3334: 3296: 3293: 3259:conjugate acid 3246: 3243: 3227:organometallic 3210: 3207: 3160: 3157: 3148: 3145: 3144: 3143: 3133: 3115:organometallic 3110: 3107: 3106: 3105: 3097: 3089: 3083: 3082: 3071: 3060: 3049: 3038: 3027: 3016: 3005: 2994: 2983: 2972: 2961: 2950: 2939: 2928: 2920: 2919: 2908: 2897: 2886: 2875: 2864: 2853: 2842: 2831: 2820: 2809: 2798: 2787: 2776: 2765: 2757: 2756: 2752: 2751: 2740: 2729: 2718: 2707: 2696: 2685: 2674: 2663: 2652: 2641: 2630: 2619: 2608: 2597: 2586: 2575: 2568: 2557: 2546: 2540: 2539: 2528: 2517: 2506: 2495: 2484: 2473: 2462: 2451: 2440: 2429: 2418: 2407: 2396: 2385: 2374: 2363: 2356: 2345: 2334: 2328: 2327: 2316: 2305: 2294: 2283: 2272: 2261: 2250: 2239: 2228: 2217: 2206: 2195: 2184: 2173: 2162: 2151: 2149: 2138: 2127: 2121: 2120: 2109: 2098: 2087: 2076: 2065: 2054: 2043: 2032: 2021: 2010: 1999: 1988: 1977: 1966: 1955: 1944: 1942: 1931: 1920: 1914: 1913: 1902: 1891: 1880: 1869: 1858: 1847: 1844: 1833: 1822: 1816: 1815: 1804: 1793: 1782: 1771: 1760: 1749: 1746: 1735: 1724: 1718: 1717: 1706: 1703: 1692: 1686: 1685: 1682: 1675: 1674: 1669: 1664: 1659: 1654: 1649: 1644: 1639: 1634: 1629: 1624: 1619: 1614: 1609: 1604: 1599: 1594: 1592: 1587: 1582: 1575: 1574: 1570:Periodic table 1568: 1566: 1565: 1558: 1551: 1543: 1526: 1522: 1518: 1510: 1469:periodic table 1444: 1441: 1423:. The carbene 1386:deprotonations 1366:cycloadditions 1348:), performing 1330: 1329: 1326: 1323: 1320: 1318: 1315: 1311: 1308: 1304: 1303: 1300: 1297: 1294: 1292: 1289: 1285: 1281: 1278: 1274: 1273: 1270: 1266: 1263: 1260: 1258: 1255: 1252: 1248: 1247: 1244: 1241: 1238: 1236: 1233: 1230: 1208: 1205: 1168:dimerisation: 1161: 1157: 1153: 1149: 1119: 1088: 1085: 1080: 1073: 1020: 1011: 1008: 1006: 1003: 980:Main article: 977: 974: 972:being 85.7°). 970:dihedral angle 846: 843: 830: 827: 790: 787: 774: 771: 763:1,3-dithiolium 754: 746: 743: 739:dichalcogenide 675: 672: 642: 639: 609:1,2,4-triazole 589: 586: 561:effect of the 528:substituents: 502: 499: 494: 491: 447: 415: 353: 350: 259:isothiocyanate 243:Roald Hoffmann 234: 231: 189:was reported. 138: 135:derivative of 125:Ronald Breslow 120: 119:Early evidence 117: 115: 112: 91:stabilized by 53:whose natural 47:stable carbene 26: 24: 14: 13: 10: 9: 6: 4: 3: 2: 6487: 6476: 6473: 6471: 6468: 6466: 6463: 6461: 6458: 6457: 6455: 6444: 6440: 6436: 6432: 6428: 6425: 6424: 6418: 6417: 6416: 6409: 6405: 6401: 6398: 6397: 6391: 6388: 6386: 6383: 6381: 6378: 6373: 6369: 6365: 6361: 6357: 6353: 6349: 6345: 6341: 6337: 6336: 6330: 6329: 6328: 6322: 6314: 6310: 6306: 6302: 6298: 6295: 6294: 6285: 6282: 6277: 6273: 6269: 6266: 6265: 6257: 6254: 6249: 6245: 6241: 6237: 6236: 6231: 6224: 6221: 6216: 6212: 6208: 6207: 6198: 6195: 6190: 6186: 6182: 6178: 6174: 6170: 6166: 6162: 6155: 6152: 6147: 6143: 6139: 6135: 6131: 6127: 6123: 6119: 6115: 6112: 6111: 6103: 6100: 6097: 6096:3-540-36929-5 6093: 6089: 6083: 6080: 6077: 6076:3-527-31400-8 6073: 6069: 6063: 6060: 6054: 6049: 6045: 6041: 6040: 6035: 6028: 6025: 6020: 6016: 6012: 6009: 6008: 6000: 5997: 5992: 5988: 5984: 5981: 5980: 5975: 5969: 5967: 5963: 5958: 5954: 5950: 5947: 5946: 5941: 5937: 5931: 5929: 5925: 5920: 5916: 5912: 5909: 5908: 5900: 5898: 5894: 5889: 5885: 5881: 5878: 5877: 5872: 5865: 5862: 5857: 5853: 5849: 5845: 5841: 5838: 5837: 5832: 5828: 5822: 5820: 5816: 5811: 5807: 5803: 5800: 5799: 5791: 5788: 5783: 5779: 5775: 5771: 5767: 5764: 5763: 5755: 5753: 5749: 5744: 5740: 5736: 5732: 5728: 5725: 5724: 5716: 5713: 5708: 5704: 5700: 5697: 5696: 5691: 5684: 5682: 5678: 5673: 5669: 5665: 5662: 5661: 5656: 5649: 5646: 5641: 5637: 5632: 5627: 5623: 5620: 5619: 5614: 5607: 5604: 5599: 5595: 5591: 5588: 5587: 5579: 5576: 5571: 5567: 5563: 5559: 5555: 5551: 5547: 5544: 5543: 5542:Chem. Commun. 5538: 5536: 5529: 5520: 5517: 5512: 5508: 5504: 5500: 5496: 5493: 5492: 5484: 5477: 5474: 5469: 5465: 5461: 5460: 5459:Chem. Commun. 5452: 5450: 5446: 5441: 5437: 5433: 5429: 5425: 5422: 5421: 5413: 5410: 5405: 5401: 5397: 5393: 5392: 5387: 5380: 5377: 5372: 5368: 5364: 5360: 5356: 5352: 5348: 5344: 5340: 5336: 5335: 5327: 5324: 5319: 5315: 5310: 5305: 5301: 5297: 5293: 5290: 5289: 5284: 5282: 5273: 5271: 5267: 5262: 5258: 5254: 5251: 5250: 5242: 5239: 5234: 5230: 5226: 5223: 5222: 5214: 5212: 5208: 5203: 5199: 5195: 5192: 5191: 5183: 5181: 5177: 5172: 5168: 5164: 5161: 5160: 5152: 5149: 5144: 5140: 5136: 5135: 5134:Chem. Commun. 5127: 5125: 5123: 5121: 5117: 5112: 5108: 5104: 5101: 5100: 5095: 5088: 5086: 5084: 5082: 5078: 5073: 5069: 5065: 5062: 5061: 5053: 5051: 5047: 5042: 5038: 5034: 5031: 5030: 5029:Chem. Eur. J. 5025: 5018: 5016: 5012: 5007: 5003: 4999: 4996: 4995: 4994:Chem. Eur. J. 4990: 4983: 4981: 4979: 4975: 4970: 4966: 4961: 4956: 4952: 4948: 4944: 4940: 4936: 4932: 4931: 4926: 4919: 4917: 4913: 4908: 4904: 4900: 4897: 4896: 4888: 4886: 4884: 4880: 4875: 4871: 4867: 4864: 4863: 4855: 4853: 4851: 4849: 4847: 4843: 4838: 4834: 4830: 4826: 4822: 4818: 4817: 4805: 4803: 4799: 4794: 4790: 4786: 4785: 4784:Chem. Commun. 4780: 4776: 4769: 4767: 4765: 4763: 4761: 4757: 4752: 4748: 4744: 4740: 4736: 4729: 4727: 4725: 4723: 4719: 4714: 4710: 4706: 4703: 4702: 4694: 4692: 4690: 4688: 4686: 4682: 4677: 4673: 4669: 4666: 4665: 4657: 4655: 4653: 4651: 4649: 4645: 4640: 4636: 4632: 4629: 4628: 4620: 4618: 4616: 4612: 4607: 4603: 4599: 4596: 4595: 4587: 4585: 4583: 4581: 4577: 4565: 4561: 4557: 4551: 4548: 4543: 4539: 4535: 4532: 4531: 4526: 4519: 4516: 4511: 4507: 4503: 4499: 4495: 4491: 4487: 4483: 4482: 4474: 4471: 4466: 4462: 4458: 4454: 4450: 4446: 4442: 4438: 4437: 4429: 4426: 4421: 4417: 4413: 4410: 4409: 4401: 4399: 4395: 4390: 4386: 4382: 4379: 4378: 4370: 4367: 4362: 4358: 4354: 4350: 4346: 4343: 4342: 4334: 4331: 4326: 4322: 4318: 4315: 4314: 4306: 4304: 4302: 4298: 4293: 4289: 4285: 4282: 4281: 4273: 4271: 4269: 4265: 4260: 4256: 4252: 4249: 4248: 4236: 4234: 4230: 4225: 4221: 4217: 4214: 4213: 4205: 4202: 4197: 4193: 4189: 4186: 4185: 4176: 4174: 4170: 4165: 4161: 4157: 4153: 4149: 4146: 4145: 4137: 4134: 4129: 4125: 4121: 4118: 4117: 4109: 4106: 4101: 4097: 4093: 4090: 4089: 4081: 4078: 4073: 4069: 4065: 4062: 4061: 4053: 4050: 4045: 4041: 4037: 4034: 4033: 4025: 4023: 4019: 4014: 4010: 4006: 4003: 4002: 3994: 3992: 3988: 3983: 3979: 3975: 3971: 3967: 3964: 3963: 3955: 3952: 3949: 3944: 3941: 3936: 3932: 3927: 3922: 3918: 3915: 3914: 3909: 3907: 3904:"Umpolung by 3898: 3895: 3890: 3886: 3882: 3879: 3878: 3870: 3867: 3862: 3858: 3854: 3851: 3850: 3842: 3839: 3834: 3831: 3830: 3825: 3819: 3816: 3811: 3807: 3803: 3799: 3795: 3791: 3787: 3783: 3779: 3775: 3774: 3769: 3762: 3759: 3753: 3751: 3749: 3744: 3740: 3736: 3732: 3728: 3719: 3712: 3710: 3708: 3704: 3703:photochemical 3696: 3637: 3636: 3635: 3633: 3629: 3625: 3605: 3598: 3592: 3588: 3586: 3582: 3578: 3569: 3567: 3565: 3561: 3552: 3548: 3546: 3542: 3538: 3537:deoxygenation 3534: 3530: 3526: 3522: 3518: 3510: 3508: 3505: 3503: 3499: 3494: 3493:formamidinium 3490: 3486: 3481: 3474: 3469: 3462: 3460: 3458: 3454: 3453:-butyllithium 3452: 3447: 3443: 3439: 3431: 3426: 3425:formamidinium 3423:Reduction of 3421: 3417: 3415: 3410: 3409:alkyllithiums 3403:Alkyllithiums 3402: 3400: 3398: 3393: 3389: 3385: 3381: 3376: 3374: 3370: 3366: 3362: 3360: 3355: 3351: 3347: 3343: 3335: 3333: 3331: 3326: 3324: 3320: 3316: 3307: 3303: 3301: 3300:Deprotonation 3295:Deprotonation 3294: 3292: 3289: 3287: 3282: 3280: 3279:formamidinium 3276: 3272: 3268: 3264: 3260: 3257:value of the 3256: 3252: 3244: 3242: 3240: 3236: 3232: 3228: 3224: 3215: 3208: 3206: 3204: 3200: 3196: 3192: 3188: 3183: 3181: 3177: 3172: 3165: 3158: 3156: 3154: 3146: 3141: 3137: 3134: 3131: 3127: 3124: 3123: 3122: 3120: 3116: 3108: 3098: 3090: 3087: 3086: 3080: 3069: 3058: 3047: 3036: 3025: 3014: 3003: 2992: 2981: 2970: 2959: 2948: 2937: 2921: 2917: 2906: 2895: 2884: 2873: 2862: 2851: 2840: 2829: 2818: 2807: 2796: 2785: 2774: 2758: 2753: 2749: 2738: 2727: 2716: 2705: 2694: 2683: 2672: 2661: 2650: 2639: 2628: 2617: 2606: 2595: 2584: 2569: 2566: 2555: 2545: 2542: 2541: 2537: 2526: 2515: 2504: 2493: 2482: 2471: 2460: 2449: 2438: 2427: 2416: 2405: 2394: 2383: 2372: 2357: 2354: 2343: 2333: 2330: 2329: 2325: 2314: 2303: 2292: 2281: 2270: 2259: 2248: 2237: 2226: 2215: 2204: 2193: 2182: 2171: 2160: 2150: 2147: 2136: 2126: 2123: 2122: 2118: 2107: 2096: 2085: 2074: 2063: 2052: 2041: 2030: 2019: 2008: 1997: 1986: 1975: 1964: 1953: 1943: 1940: 1929: 1919: 1916: 1915: 1911: 1900: 1889: 1878: 1867: 1856: 1842: 1831: 1821: 1818: 1817: 1813: 1802: 1791: 1780: 1769: 1758: 1744: 1733: 1723: 1720: 1719: 1715: 1701: 1691: 1688: 1687: 1681: 1677: 1676: 1673: 1668: 1663: 1658: 1653: 1648: 1643: 1638: 1633: 1628: 1623: 1618: 1613: 1608: 1603: 1598: 1593: 1591: 1586: 1580: 1576: 1571: 1564: 1559: 1557: 1552: 1550: 1545: 1544: 1541: 1538: 1536: 1532: 1517:catalyst RuCl 1516: 1508: 1504: 1501: 1497: 1493: 1492:back-donation 1490: 1486: 1482: 1478: 1474: 1470: 1466: 1462: 1458: 1454: 1450: 1449:alkali metals 1442: 1437: 1432: 1428: 1426: 1422: 1418: 1414: 1410: 1406: 1402: 1398: 1393: 1391: 1387: 1383: 1379: 1375: 1371: 1367: 1363: 1359: 1355: 1351: 1347: 1343: 1339: 1327: 1324: 1321: 1319: 1316: 1309: 1306: 1305: 1301: 1298: 1295: 1293: 1290: 1279: 1276: 1275: 1271: 1264: 1261: 1259: 1256: 1253: 1250: 1249: 1245: 1242: 1239: 1237: 1234: 1231: 1228: 1227: 1220: 1216: 1214: 1206: 1204: 1202: 1198: 1194: 1193:singlet state 1190: 1189:triplet state 1185: 1182: 1181:formamidinium 1173: 1169: 1167: 1166:singlet state 1146: 1144: 1140: 1139:electrostatic 1136: 1127: 1123: 1117: 1113: 1112:deprotonating 1108: 1106: 1102: 1098: 1094: 1086: 1084: 1079: 1072: 1067: 1065: 1061: 1057: 1056:1-bromohexane 1049: 1044: 1040: 1033: 1029: 1027: 1023: 1019: 1009: 1004: 1002: 1000: 996: 992: 988: 983: 975: 973: 971: 967: 963: 959: 955: 951: 947: 943: 934: 930: 928: 924: 923:hybridisation 920: 916: 911: 909: 905: 901: 897: 896:decomposition 894: 893:photochemical 890: 881: 877: 875: 870: 868: 864: 860: 856: 855:Hideo Tomioka 852: 844: 842: 840: 836: 828: 823: 819: 814: 810: 808: 804: 800: 796: 788: 786: 784: 780: 770: 768: 764: 760: 752: 744: 742: 740: 736: 732: 728: 723: 720: 716: 712: 707: 705: 701: 697: 688: 684: 682: 673: 671: 667: 665: 655: 651: 649: 640: 638: 636: 632: 628: 620: 616: 614: 610: 607:based on the 606: 597: 593: 587: 585: 581: 578: 576: 572: 568: 564: 560: 556: 548: 541: 533: 529: 527: 523: 519: 514: 512: 508: 500: 498: 492: 487: 482: 478: 476: 472: 468: 464: 460: 456: 451: 444: 440: 436: 427: 423: 421: 413: 409: 405: 401: 397: 389: 384: 380: 378: 374: 370: 362: 358: 351: 349: 345: 342: 340: 336: 332: 323: 316: 311: 307: 305: 304:deprotonation 300: 298: 289: 285: 283: 279: 275: 266: 262: 260: 256: 252: 248: 244: 240: 232: 230: 227: 223: 219: 215: 211: 207: 203: 199: 195: 190: 188: 179: 175: 173: 169: 165: 161: 157: 153: 149: 145: 141: 134: 130: 126: 118: 113: 111: 109: 105: 100: 98: 94: 90: 86: 82: 77: 75: 71: 69: 64: 60: 56: 52: 48: 44: 36: 32: 19: 6426: 6421: 6414: 6399: 6394: 6339: 6333: 6326: 6296: 6291: 6284: 6267: 6262: 6256: 6239: 6233: 6232:)-thiones". 6229: 6223: 6204: 6197: 6164: 6160: 6154: 6113: 6108: 6102: 6082: 6070:, Wiley-VCH 6062: 6043: 6037: 6027: 6010: 6005: 5999: 5982: 5977: 5948: 5943: 5939: 5910: 5905: 5879: 5874: 5870: 5864: 5839: 5834: 5830: 5804:(36): 6926. 5801: 5796: 5790: 5765: 5760: 5726: 5721: 5715: 5698: 5693: 5689: 5663: 5658: 5654: 5648: 5621: 5616: 5606: 5589: 5584: 5578: 5545: 5540: 5534: 5527: 5519: 5494: 5489: 5476: 5462:(12): 1267. 5457: 5423: 5418: 5412: 5395: 5389: 5379: 5338: 5332: 5326: 5291: 5286: 5280: 5252: 5247: 5241: 5224: 5219: 5193: 5188: 5162: 5157: 5151: 5132: 5102: 5097: 5093: 5063: 5058: 5032: 5027: 5023: 4997: 4992: 4988: 4934: 4928: 4898: 4893: 4865: 4860: 4820: 4814: 4782: 4778: 4774: 4734: 4704: 4699: 4667: 4662: 4630: 4625: 4597: 4592: 4567:. Retrieved 4563: 4556:Rzepa, Henry 4550: 4533: 4528: 4524: 4518: 4485: 4479: 4473: 4440: 4434: 4428: 4411: 4406: 4380: 4375: 4369: 4344: 4339: 4333: 4316: 4311: 4283: 4278: 4250: 4245: 4215: 4210: 4204: 4187: 4182: 4147: 4142: 4136: 4119: 4114: 4108: 4091: 4086: 4080: 4063: 4058: 4052: 4038:(2): 75–80. 4035: 4030: 4004: 3999: 3965: 3962:Angew. Chem. 3960: 3954: 3943: 3916: 3911: 3905: 3897: 3880: 3875: 3869: 3852: 3847: 3841: 3832: 3827: 3818: 3777: 3771: 3767: 3761: 3730: 3724: 3713:Purification 3700: 3602: 3584: 3580: 3573: 3557: 3514: 3506: 3502:crown ethers 3482: 3478: 3450: 3435: 3432:Amides bases 3406: 3377: 3369:dimsyl anion 3358: 3339: 3327: 3312: 3298: 3290: 3285: 3283: 3275:nucleophilic 3248: 3220: 3209:Applications 3203:trans effect 3198: 3194: 3190: 3186: 3184: 3173: 3170: 3150: 3112: 1446: 1435: 1424: 1416: 1412: 1408: 1404: 1400: 1394: 1389: 1381: 1377: 1373: 1369: 1361: 1353: 1345: 1341: 1338:nucleophilic 1335: 1212: 1210: 1186: 1178: 1147: 1132: 1109: 1090: 1087:Dimerisation 1077: 1070: 1068: 1064:nucleophilic 1053: 1038: 1017: 1013: 998: 994: 990: 985: 942:benzophenone 939: 912: 900:diazomethane 886: 871: 848: 832: 794: 792: 776: 748: 730: 724: 708: 693: 677: 668: 660: 644: 625: 602: 591: 582: 579: 552: 515: 504: 496: 452: 432: 407: 395: 393: 373:dative bonds 366: 346: 343: 335:bond lengths 327: 318: 314: 301: 294: 274:Guy Bertrand 271: 236: 191: 186: 184: 146:that yields 129:nucleophilic 122: 101: 85:ground state 78: 73: 67: 66: 46: 42: 40: 6090:, Springer 5701:: 397–399. 4286:: 323–355. 4190:: 176–179. 3968:(14): 494. 3743:sublimation 3646:Si−Hg−Si(CH 3626:and chloro- 3614:Si-Hg-Si(CH 3579:of adducts 3407:The use of 3319:imidazolium 1505:in several 1461:lanthanides 1397:isothiazole 1152:N–C–OR or R 793:One stable 648:Roger Alder 635:nucleophile 471:heteroatoms 459:double bond 439:aromaticity 339:double bond 247:aromaticity 239:imidazolium 172:equilibrium 131:carbene, a 6454:Categories 6110:Chem. Rev. 5907:Chem. Ber. 5398:(33): 11. 4341:Chem. Rev. 4001:Chem. Ber. 3829:Chem. Ind. 3754:References 1535:tridentate 1207:Reactivity 1135:lone pairs 966:bond angle 962:picometers 919:orthogonal 874:orthogonal 822:cyclohexyl 779:phosphorus 727:chalcogens 704:oxyiminium 681:phosphorus 467:octet rule 379:orbitals. 210:chloroform 156:thiazolium 6235:Synthesis 6161:Chem. Rev 6146:206902952 6130:0009-2665 5570:205757477 3628:amidinium 3564:potassium 3525:potassium 3521:thioureas 3498:cryptands 3440:and the ( 3414:isobutene 3384:potassium 3373:hydroxide 3365:catalysts 3350:inorganic 3330:precursor 3231:ruthenium 1531:bidentate 1500:phosphine 1494:from the 1485:lone pair 1465:actinides 1459:and even 1411:-thiete ( 1399:carbene ( 1340:fashion ( 1201:p-orbital 1197:lone pair 889:half-life 867:half-life 801:with one 759:acetylene 741:(X=C=X). 575:induction 571:lone pair 507:imidazole 443:imidazole 418:ImC:), a 400:adamantyl 369:resonance 272:In 1988, 192:In 1960, 162:, the C2- 137:vitamin B 123:In 1957, 6465:Carbenes 6443:20715233 6364:24965649 6313:14746458 6189:43090499 6181:16277368 6138:19588961 5856:97336589 5782:17661300 5743:17372997 5640:15457494 5562:21116519 5511:23173841 5440:16417387 5363:11493917 5318:16028925 4969:16614171 4751:15467857 4510:11397943 4465:10796999 4361:19281270 4164:11093196 3935:23081675 3802:24965649 3707:nitrogen 3658:N=C(Cl)− 3545:fluorene 3346:hydrogen 3281:salts). 3153:carbenes 1581: → 1496:nitrogen 1254:RXH, RT 1105:aromatic 1101:solution 1093:dimerise 1028:(DMSO): 958:distance 927:orbitals 908:nitrogen 799:borazine 715:divalent 696:thiazole 627:Triazole 563:chlorine 555:chlorine 455:hindered 168:deuteron 152:furfural 81:misnomer 49:) is an 6344:Bibcode 5371:4373216 5343:Bibcode 5309:2440681 4960:2427275 4939:Bibcode 4930:Science 4825:Bibcode 4811:carbene 4490:Bibcode 4481:Science 4445:Bibcode 4436:Science 3970:Bibcode 3782:Bibcode 3748:lithium 3632:mercury 3624:iminium 3543:with a 3388:ammonia 3271:acidity 3233:-based 3136:Schrock 3126:Fischer 1678:↓ 1503:ligands 1481:ligands 1317:25–68% 1302:47–84% 1291:54–68% 1272:71–90% 1257:95–97% 1143:carbene 1048:D6-DMSO 964:with a 950:bromine 851:singlet 783:silicon 404:prevent 377:pi-bond 297:alkynic 255:mercury 114:History 104:ligands 63:carbene 6441: 6372:672379 6370: 6362: 6335:Nature 6311: 6187: 6179: 6144: 6136: 6128: 6094: 6074: 5854: 5780: 5741: 5638: 5568: 5560: 5509: 5438: 5369: 5361: 5334:Nature 5316: 5306: 4967: 4957: 4749: 4569:15 Feb 4508: 4463: 4359: 4162: 3933: 3835:: 893. 3810:672379 3808: 3800: 3773:Nature 3731:per se 3684:+ 2(CH 3674:N−C−NR 3670:Cl → R 3380:sodium 3263:oxygen 3187:et al. 3101: 3093: 3088:Legend 1680:Period 1489:ligand 1213:et al. 1160:N–C–NR 1060:alkene 1046:Using 956:, the 915:phenyl 781:and a 735:alkyne 719:steric 711:oxygen 709:Since 573:, via 526:chiral 477:ring. 412:methyl 164:proton 148:furoin 6368:S2CID 6185:S2CID 6142:S2CID 5852:S2CID 5566:S2CID 5486:(PDF) 5367:S2CID 3806:S2CID 3539:of a 3523:with 3489:KHMDS 3473:KHMDS 3361:-BuOH 3253:(the 3251:basic 3195:trans 3191:trans 1579:Group 910:gas. 898:of a 818:LiTMP 803:boron 700:thio- 518:alkyl 371:with 331:X-ray 253:with 226:Lemal 214:dimer 150:from 89:ylide 6439:PMID 6360:PMID 6309:PMID 6240:1993 6177:PMID 6134:PMID 6126:ISSN 6092:ISBN 6072:ISBN 5871:tert 5778:PMID 5739:PMID 5664:1996 5636:PMID 5558:PMID 5507:PMID 5436:PMID 5359:PMID 5314:PMID 4965:PMID 4866:1997 4747:PMID 4571:2024 4506:PMID 4461:PMID 4357:PMID 4160:PMID 3931:PMID 3798:PMID 3692:SiCl 3678:+ Hg 3558:The 3541:urea 3485:HMDS 3446:LiOH 3354:DMSO 3321:and 3315:IMes 3286:situ 3237:and 1533:and 1521:(PCy 1467:. 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