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Heterocyclic carbene

Another aspect of this problem is the existence of heterocyclic carbenes containing a low-valent gallium center, 49 (95JA5421,98EJIC305,99JA9758, 01 JCS(D)3459). 1,4-Bis(2,6-di-Ao-propylphenyl)-l, 4-diazabuta-l, 3-diene... [Pg.21]

As well as phosphorus ligands, heterocyclic carbenes ligands 10 have proven to be interesting donor ligands for stabilization of transition metal complexes (especially palladium) in ionic liquids. The imidazolium cation is usually presumed to be a simple inert component of the solvent system. However, the proton on the carbon atom at position 2 in the imidazolium is acidic and this carbon atom can be depro-tonated by, for example, basic ligands of the metal complex, to form carbenes (Scheme 5.3-2). [Pg.269]

The ease of formation of the carbene depends on the nucleophilicity of the anion associated with the imidazolium. For example, when Pd(OAc)2 is heated in the presence of [BMIM][Br], the formation of a mixture of Pd imidazolylidene complexes occurs. Palladium complexes have been shown to be active and stable catalysts for Heck and other C-C coupling reactions [34]. The highest activity and stability of palladium is observed in the ionic liquid [BMIM][Brj. Carbene complexes can be formed not only by deprotonation of the imidazolium cation but also by direct oxidative addition to metal(O) (Scheme 5.3-3). These heterocyclic carbene ligands can be functionalized with polar groups in order to increase their affinity for ionic liquids. While their donor properties can be compared to those of donor phosphines, they have the advantage over phosphines of being stable toward oxidation. [Pg.269]

The surprising stability of N-heterocyclic carbenes was of interest to organometallic chemists who started to explore the metal complexes of these new ligands. The first examples of this class had been synthesized as early as 1968 by Wanzlick [9] and Ofele [10], only 4 years after the first Fischer-type carbene complex was synthesized [2,3] and 6 years before the first report of a Schrock-type carbene complex [11]. Once the N-heterocyclic ligands are attached to a metal they show a completely different reaction pattern compared to the electrophilic Fischer- and nucleophilic Schrock-type carbene complexes. [Pg.2]

During the last decade N-heterocyclic carbene complexes of transition metals have been developed for catalytic applications for many different or-... [Pg.3]

Scheme 3 Different classes of synthesized (AT-heterocyclic) carbenes... Scheme 3 Different classes of synthesized (AT-heterocyclic) carbenes...
AT-heterocyclic carbenes show a pure donor nature. Comparing them to other monodentate ligands such as phosphines and amines on several metal-carbonyl complexes showed the significantly increased donor capacity relative to phosphines, even to trialkylphosphines, while the 7r-acceptor capability of the NHCs is in the order of those of nitriles and pyridine [29]. This was used to synthesize the metathesis catalysts discussed in the next section. Experimental evidence comes from the fact that it has been shown for several metals that an exchange of phosphines versus NHCs proceeds rapidly and without the need of an excess quantity of the NHC. X-ray structures of the NHC complexes show exceptionally long metal-carbon bonds indicating a different type of bond compared to the Schrock-type carbene double bond. As a result, the reactivity of these NHC complexes is also unique. They are relatively resistant towards an attack by nucleophiles and electrophiles at the divalent carbon atom. [Pg.12]

Diamino-substituted complexes of type 37 were first obtained by Fischer et al. [12] in two steps via the 1,2-addition-elimination product 34 from di-methylamine and 35 (Scheme 6). The (3-aminoallenylidene)chromium complexes 36, which can be prepared either from 33 [47,48] or directly from 35 [33], can also be transformed to l,3-bis(dialkylamino)-substituted complexes of type 37 (e.g., R2=z Pr) by treatment with dimethylamine in excellent yields [33]. Although the complex 37 is accessible by further reaction of the complex 34 with dimethylamine, and 34 itself stems from the reaction of 35 with dimethylamine, the direct transformation of 33 to 37 could not be achieved [12]. In spite of this, heterocyclic carbene complexes with two nitrogens were obtained by reactions of alkynylcarbene complexes 35 with hydrazine [49] and 1,3-diamines [50]. [Pg.27]

Ruthenium Precatalysts with N-Heterocyclic Carbene Ligands.238... [Pg.223]

Table 3 Ruthenium alkylidene complexes with JV-heterocyclic carbene ligands... Table 3 Ruthenium alkylidene complexes with JV-heterocyclic carbene ligands...
The search for even more active and recyclable ruthenium-based metathesis catalysts has recently led to the development of phosphine-free complexes by combining the concept of ligation with N-heterocyclic carbenes and benzyli-denes bearing a coordinating isopropoxy ligand. The latter was exemplified for Hoveyda s monophosphine complex 13 in Scheme 5 [12]. Pioneering studies in this field have been conducted by the groups of Hoveyda [49a] and Blechert [49b], who described the phosphine-free precatalyst 71a. Compound 71a is prepared either from 56d [49a] or from 13 [49b], as illustrated in Scheme 16. [Pg.245]

Independently, Caddick et al. reported microwave-assisted amination of aryl chlorides using a palladium-N-heterocyclic carbene complex as the catalyst (Scheme 99) [lOlj. Initial experiments in a domestic microwave oven (reflux conditions) revealed that the solvent is crucial for the reaction. The Pd source also proved very important, since Pd(OAc)2 at high power in DMF gave extensive catalyst decomposition and using it at medium and low power gave no reaction at all. Pd(dba)2/imidazohum salt (1 mol% catalyst loading) in DME with the addition of some DMF was found to be suitable. Oil bath experiments indicated that only thermal effects are governing the amination reactions. [Pg.203]

Synthesis of Chiral AJ-heterocyclic Carbenes and of Their Complexes. .. 194... [Pg.191]

M-heterocyclic carbenes are neutral compounds with a divalent carbon atom located between the two nitrogens. The four types of stable diaminocarbenes used for the synthesis of chiral complexes are listed below (Fig. 2) ... [Pg.192]

AT-heterocyclic carbene complexes of Pd(II) or Pd(0) were extensively used in various reactions and several groups have reported syntheses of chiral complexes [5]. However, only a few examples of asymmetric catalysis are... [Pg.205]

Nolan SP, Viciu MS (2005) The Use of N-Heterocyclic Carbenes as Ligands in Palladium Mediated Catalysis. 14 241-278... [Pg.293]


See other pages where Heterocyclic carbene is mentioned: [Pg.206]    [Pg.12]    [Pg.138]    [Pg.238]    [Pg.238]    [Pg.261]    [Pg.263]    [Pg.270]    [Pg.274]    [Pg.329]    [Pg.433]    [Pg.210]    [Pg.208]    [Pg.87]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.191]    [Pg.192]    [Pg.192]    [Pg.205]    [Pg.206]    [Pg.210]    [Pg.212]    [Pg.215]    [Pg.220]    [Pg.223]   
See also in sourсe #XX -- [ Pg.45 ]




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A -Heterocyclic carbene ligands

A-Heterocyclic Carbene-based Complexes

A-Heterocyclic carbene catalysts

A-Heterocyclic carbenes ligands

A-heterocyclic carbene

A-heterocyclic carbenes

A-heterocyclic carbenes catalysts

A-heterocyclic carbenes complexes

Af-heterocyclic carbene

Al-Heterocyclic Carbenes (NHCs) as Ligands in Transition-Metal-Catalyzed Hydroformylation

Al-heterocyclic carbenes

Bidentate N-Heterocyclic Carbene Ligands Incorporating Oxazoline Units

Boron-containing heterocyclic carbenes

Carbene, -heterocyclic, chelating

Carbene, chiral heterocyclic

Carbenes Derived from Five-membered Heterocycles

Carbenes Derived from Four-membered Heterocycles

Carbenes and nitrenes in heterocyclic

Carbenes and nitrenes in heterocyclic chemistry, intramolecular reactions

Carbenes heterocyclic

Carbenes heterocyclic

Carbenes nitrogen-free heterocyclic

Carbenes, heterocyclic, ring-cleavage

Carbenes, reaction with heterocyclic

Carbenes, reaction with heterocyclic compounds

Chiral N-heterocyclic carbenes

Copper N-heterocyclic carbene complexe

Early Transition and Rare Earth Metal Complexes with N-Heterocyclic Carbenes

Enantioselective heterocyclic carbene catalysts

Five-membered heterocycle-derived carbenes

Five-membered heterocycles reactions with carbenes

Four-membered heterocycle-derived carbenes

Free N-heterocyclic carbenes

Functionalised N-heterocyclic carbenes

General Carbene Routes to Heterocycles

Heterocycles from carbenes

Heterocycles reaction with carbenes

Heterocycles, acylation metal carbenes

Heterocyclic Carbenes Containing Boron within the Heterocycle

Heterocyclic compounds reactions of, with carbenes

Hydrogen-bonded heterocyclic carbenes

IV-Heterocyclic carbenes

IV-heterocyclic carbene

IV-heterocyclic carbene ligand

Iridium N-Heterocyclic Carbene Complexes and Their Application as Homogeneous Catalysts

Iridium N-heterocyclic carbene complexe

Iridium N-heterocyclic carbene complexes

JV-Heterocyclic carbenes

Ligand Design for A-Heterocyclic Carbenes (NHC)

Ligands N-heterocyclic carbenes

Metal-carbene complexes Heterocyclics

N-Heterocyclic Carbenes Derived from Six- or Seven-membered Heterocycles

N-Heterocyclic Carbenes Synthesis and Stereoelectronic Parameters

N-Heterocyclic Carbenes as Asymmetric Organocatalysts

N-Heterocyclic Carbenes: Effective Tools for Organometallic Synthesis, First Edition. Edited by Steven P. Nolan

N-Heterocyclic Carbenes: Effective Tools for Organometallic Synthesis, First Edition. Edited by Steven P. Nolan Au

N-Heterocyclic carbene (NHC

N-Heterocyclic carbene catalysis

N-Heterocyclic carbenes NHCs)

N-Heterocyclic carbenes complexes

N-heterocyclic carbene

N-heterocyclic carbene Cl

N-heterocyclic carbene ligand

N-heterocyclic carbene ligands NHCs)

N-heterocyclic carbene ligands and

N-heterocyclic carbene synthesis

N-heterocyclic carbenes

N-heterocyclic carbenes metal complexes

N-heterocyclic carbenes stabilization

N-heterocyclic carbenes synthesis

N-heterocyclic carbenes, as ligands

N-heterocyclic-carbene complexes

Nitrogen-heterocyclic carbene

Non-classical N-Heterocyclic Carbene Complexes

Nucleophilic heterocyclic carbene

Nucleophilic heterocyclic carbene ligands

Organometallic compounds heterocyclic carbenes

P-heterocyclic carbenes

Palladium N-heterocyclic carbene

Palladium N-heterocyclic carbene complexes

Pd-N-heterocyclic carbene complexes

Rhodium heterocyclic carbenes

Ruthenium N-heterocyclic carbene

Ruthenium N-heterocyclic carbene complexes

Seven-membered heterocycle-derived carbenes

Synthesis of N-heterocyclic carbene

TV-heterocyclic carbene

TV-heterocyclic carbenes

The Nature of N-Heterocyclic Carbenes

Unsaturated N-heterocyclic carbenes

V-Heterocyclic carbene

V-Heterocyclic carbene complexes

V-Heterocyclic carbene ligands

W-Heterocyclic carbenes

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