Diaminocarbene‐ and Fischer‐Carbene Complexes of Palladium and Nickel by Oxidative Insertion: Preparation, Structure, and Catalytic Activity

Kremzow, Doris; Seidel, Günter; Lehmann, Christian W.; Fürstner, Alois

doi:10.1002/chem.200400928

Cited by 218 publications

(122 citation statements)

References 180 publications

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“…Werden hingegen Salze von schwach koordinierenden Anionen wie BF 4 À oder PF 6 À in Acetonitril verwendet, entstehen die kationischen Palladium-AcetonitrilKomplexe, die in Form ihrer BF 4 -oder PF 6 -Salze isoliert werden (Schema 30). [98,104] Schließlich inserieren Pd 0 -Spezies oxidativ in C-H-, [95] C-Cl- [107] und C-S-Bindungen [108] (Schema [32][33][34] …”

Section: Allgemeine Synthesemethoden Für Pd-nhc-komplexeunclassified

“…[147] Dabei kuppelten Alkyltosylate und -mesylate mit hohen Ausbeuten, die Arylanaloga erwiesen sich dagegen als unreaktiv. Die Alkylsulfonate wandeln sich vor der oxidativen Insertion durch eine S N 2-Reaktion [159] [44,48,49,92,100,107,[165][166][167][168][169][170][171][172] Die Stabilität der Pd-NHC-Spezies wurde auch genutzt, um diese Katalysatoren auf Polymerträgern zu immobilisieren [173][174][175][176][177] oder in ionischen Flüssigkeiten einzusetzen. [178,179] peln (Schema 58), musste das Spirocyclododecyl-Analogon bei 100-110 8C als Ligand eingesetzt werden (51, Schema 31).…”

Section: Die Negishi-reaktionunclassified

“…B. 418, 419; Abbildung 10; 431, Schema 81) mit chiralen Pd-NHC-Komplexen [107,186,242] gute Umsätze erzielt werden. In keinem Fall gelang aber der Aufbau eines Stereozentrums, und keiner der Komplexe wurde für asymmetrische Heck-Mizoroki-Reaktionen eingesetzt.…”

Section: G Organ Et Alunclassified

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Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

2007

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Palladiumkatalysierte C‐C‐ und C‐N‐Kupplungen zählen zu den vielseitigsten und leistungsfähigsten Syntheseverfahren. Seit 15 Jahren erfreuen sich die N‐heterocyclischen Carbene (NHCs) wachsender Beliebtheit als Liganden für palladiumvermittelte Kreuzkupplungen und ähnliche Methoden. Sie sind in vielerlei Hinsicht den üblichen tertiären Phosphanen überlegen. Weil NHCs stark σ‐elektronenschiebend sind, können sie auch anspruchsvolle Substrate zu oxidativen Insertionen bewegen. Andererseits führen ihre Sperrigkeit und ihre besondere Topologie zu einer raschen reduktiven Eliminierung. Schließlich tragen die starken Pd‐NHC‐Bindungen zur hohen Stabilität der aktiven Spezies bei – auch bei niedrigen Ligand/Pd‐Verhältnissen und hohen Temperaturen. Wenn erst stabile, anwenderfreundliche und leistungsstarke NHC‐Pd‐Präkatalysatoren kommerziell verfügbar sind, liegt das Ziel eines universellen Kreuzkupplungskatalysators in greifbarer Nähe. Dieser Aufsatz beschreibt zunächst die chemischen Grundlagen zu den NHC‐Pd‐Komplexen, um ihre Besonderheiten kennenzulernen. Anschließend folgt eine umfassende Diskussion zur Anwendung dieser Katalysatoren in C‐C‐ und C‐N‐Kreuzkupplungen sowie in der Carbopalladierung.

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Section: Allgemeine Synthesemethoden Für Pd-nhc-komplexeunclassified

Section: Die Negishi-reaktionunclassified

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Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

2007

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“…For pyridyl chloride substrates, elevated temperatures (70 °C) are required in order to achieve an appreciable 73% yield. 36 …”

Section: Hydroamination and Buchwald-hartwig Aminationmentioning

confidence: 99%

Non-classical N-Heterocyclic Carbene Complexes

Krüger

Albrecht²

2010

N-Heterocyclic Carbenes

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The expansion of the concept of N-heterocyclic carbenes as ligands for transition metals to mesoionic ligand systems has led to the discovery of a wide range of non-classical carbenetype ligands. These non-classical carbene-type ligands are characterised by a significantly lower heteroatom stabilisation of the (putative) free carbene, a situation that also affects the ligand donor properties and hence the reactivity of the coordinated metal centre. Based on the unique impact of non-classical carbene-type ligands, a number of attractive transition metal-catalysed processes have been disclosed in recent years, predominantly in the area of cross-coupling reactions, hydrogenations, and olefin metathesis. IntroductionThe transition metal chemistry of N-heterocyclic carbenes is dominated by 2-imidazolylidenes and their derivatives including oxazoles, thiazoles, 1,2,4-triazoles, and pyrimidines, as well as related saturated systems. Despite these formal ambiguities, non-classical variations of NHCs constitute an attractive class of ligands with great opportunities for catalysis and synthesis in general. This chapter aims to overview the most recent advances in using non-classical NHC ligands in transition metal-mediated catalysis and to illustrate the attractive prospects that emerge from these achievements. Synthesis of Non-Classical Carbene ComplexesA variety of different methods have been used for the formation of classical NHC complexes, and most of these methods are also applicable to the synthesis of non-classical NHC metal systems. Most frequently used methods for metallating cyclic non-classical carbene precursors include direct metallation via C-H bond activation, and C-X bond 13 as well as C-H bond oxidative addition. 14 Less common are transmetallation protocols, first because the relevant metal carbene precursors, especially the Ag-carbene salts, have only limited stability. 15 In addition, argentation suffers from a low regioselectivity, partially originating from the weak acidity of the proton to be removed. For example, exocyclic C-H bond activation has been observed in C2-methylated imidazolium salts, a reaction pathway that is successfully prevented when using C2-arylated imidazolium salts. 16Another key route towards metal carbene complexes involves the generation of the free carbene, either in situ or isolated, and subsequent metal coordination. While the stability of classical carbenes makes the free carbene route the method of choice for complex synthesis (and largely contributed to the enormous success of this class of ligands), the reduced heteroatom stabilisation in non-classical carbenes generally precludes the formation of free carbenes. 17 Theoretical investigations using energy decomposition analyses have shown that for example 4-imidazolylidene is about 20 kcal mol -1 less stable than its classical counterpart, 2-imidazolylidene. 18While free carbenes with low heteroatom stabilisation such as 1 (Figure 5. 2) 7Interestingly, abnormal imidazol-4-ylidene complexes have also been o...

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“…60 Phospha-and aza-palladacycles with an NHC ligand, such as 177179 (Chart 19), have been reported as well-defined catalysts for the MizorokiHeck olefination of haloarenes. 61 The palladacycle 179 showed lower activity than the phosphapalladacycles 177 and 178 for the coupling of different bromoarenes and chloroacetophenone with styrene employing Cs 2 CO 3 as base and tetrabutylammonium bromide as additive. On the contrary, complex 179 was really superior to other NHCpalladacycles when Ca(OH) 2 was added, being the only catalysts that coupled a chloroarene in quantitative yield.…”

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confidence: 95%

Heterocyclic Carbene–Metal-catalyzed Csp2–Csp2 and Csp–Csp2 Couplings Using Nonmetallic Substrates

Yus¹,

Pastor²

2013

Chemistry Letters

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The use of carbene ligands for transition-metal complexes has been developed in the last decades, being of special interest those carbenes derived from a nitrogen-containing heterocyclic system. An interesting variety of carbenemetal complexes has been tested in the MizorokiHeck reaction. In comparison, few examples can be found for the MatsudaHeck version of this coupling reaction. Additionally, the Sonogashira coupling has been also catalyzed with different carbenemetal catalysts. Ç IntroductionN-Heterocyclic carbenes (NHCs) have emerged in the last years as a new family of ligands with interesting electronic and structural properties.1 The combination of their strong ·-donor and poor ³-acceptor abilities results in good coordination stability and versatility. Consequently, the use of NHC ligands based on imidazolium ions and related heterocycles has appeared as an alternative to phosphanes in the design of new organometallic catalysts.2 One of the main advantages of employing NHC-based catalysts compared with phosphanebased ones is that they are far less prone to oxidation, allowing their prolonged use, and reuse. Although NHCs were presented as simple tertiary phophane mimics, they have been recognized as much more over the past decade. Therefore, NHC ligands have become an interesting alternative to other types of ligands in different cross-coupling catalytic reactions mediated by transition metals.3 Moreover, the easy introduction of chiral elements in the corresponding precursors have made chiral NHCs promising chiral ligands in metal-based asymmetric catalysis. 4 The comparison between phosphane and NHC ligands, from a mechanistic point of view, has been studied, clear differences being found.5 First, the possibility of carbene ligand dissociation is greatly reduced due to its stronger donor ability; and second, the reactivity of the NHCmetal complex is higher probably caused by the lack of back-donation from the metal to the carbene ligand. Jutand and co-workers studied the reactivity of monocarbene and bis(carbene) Pd(0) complexes toward the oxidative addition of aryl halides, concluding that the electronic and steric properties of the carbene ligand are important factors in this step of the catalytic process. 6 Among the carboncarbon coupling reactions, the activation of a CH from an alkene (MizorokiHeck reaction) or an alkyne (Sonogashira reaction) are of special interest. This highlight review describes the progress on the topic of NHC ligands for transition-metal-catalyzed coupling reactions, employing nonmetallic reagents. Thus, both different NHC precursors and NHCmetal complexes with catalytic activity in the Mizoroki Heck, MatsudaHeck, and Sonogashira reactions are compiled. Ç Mizoroki-Heck ReactionIn 1995, Herrmann and co-workers introduced the use of bis(NHC)Pd complexes as catalysts with long-term stability in the MizorokiHeck reaction.7 Indeed, the carbenes derived from imidazole stabilized the palladium complexes due to their pronounced donor properties, being more stable toward...

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Diaminocarbene‐ and Fischer‐Carbene Complexes of Palladium and Nickel by Oxidative Insertion: Preparation, Structure, and Catalytic Activity

Cited by 218 publications

References 180 publications

Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

Aus der Sicht des Synthetikers: Palladiumkomplexe N‐heterocyclischer Carbene als Katalysatoren für Kreuzkupplungen

Non-classical N-Heterocyclic Carbene Complexes

Heterocyclic Carbene–Metal-catalyzed Csp2–Csp2 and Csp–Csp2 Couplings Using Nonmetallic Substrates

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