Directly-Observed β-Hydrogen Elimination of a Late Transition Metal Amido Complex and Unusual Fate of Imine Byproducts

Hartwig, John F.

doi:10.1021/ja961439n

Cited by 79 publications

(69 citation statements)

References 23 publications

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“…57,58 This racemerization is proposed to result from reversible β-hydrogen elimination, which should occur more readily from complexes containing monophosphine ligands than from those containing bisphosphine ligands. 59,60 Consistent with this hypothesis, the coupling of 2-or 3-chloropyridine with enantioenriched (99% ee) α-phenethylamine gave the heteroarylamine products in high yield with > 95% ee in the presence of only 0.05 mol % of the catalyst (Table 1, entries 9 and 21).…”

Section: B Scope Of the Amination Of Heteroaryl And Aryl Chlorides mentioning

confidence: 53%

Highly Reactive, General and Long-Lived Catalysts for Palladium-Catalyzed Amination of Heteroaryl and Aryl Chlorides, Bromides, and Iodides: Scope and Structure–Activity Relationships

2008

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We describe a systematic study of the scope and relationship between ligand structure and activity for a highly efficient and selective class of catalysts for the amination of heteroaryl and aryl chlorides, bromides and iodides containing sterically hindered chelating alkylphosphines. In the presence of this catalyst, aryl and heteroaryl chlorides, bromides and iodides react with many primary amines in high yields with part-per-million quantities of palladium precursor and ligand. Many reactions of primary amines with both heteroaryl and aryl chlorides, bromides and iodides occur to completion with 0.0005-0.05 mol % catalysts. A comparison of the reactivity of this catalyst for coupling of primary amines at these loadings is made with catalysts generated from hindered monophosphines and carbenes, and these data illustrate the benefits of chelation. Thus, these complexes constitute a fourth-generation catalyst for the amination of aryl halides, whose activity complements catalysts based on monophosphines and carbenes.

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Section: B Scope Of the Amination Of Heteroaryl And Aryl Chlorides mentioning

confidence: 53%

Highly Reactive, General and Long-Lived Catalysts for Palladium-Catalyzed Amination of Heteroaryl and Aryl Chlorides, Bromides, and Iodides: Scope and Structure–Activity Relationships

2008

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“…Beta elimination plausibly passes through an agostic structure on the way to the transition state; thus, whatever favors or disfavors an agostic structure should favor or disfavor beta elimination. Hartwig [35] has noted that in similar complexes, beta elimination of an NMe 2 group is much slower than of an analogous CHMe 2 group. This observation is consistent with the idea that the amido group has a lower tendency to become agostic because the N lone pair is an alternative donor to the metal that can outcompete the C-H bond, particularly because the effective electronegativity of the C of the agostic C-H bond in question is higher than in the isopropyl case, and so the amido C-H bond is less Lewis basic.…”

Section: ð3; 4þmentioning

confidence: 99%

Sigma Bonds as Ligand Donor Groups in Transition Metal Complexes

Crabtree

2015

The Chemical Bond III

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Covalent X-H bonds, particularly where X is H, C, B, and Si, can act as Lewis base ligands in forming metal complexes of general type L n M(H-X), where the M-H-X angle is strongly bent so that the coordination can best be considered as side-on. The binding is greatly enhanced by back donation from the metal into the X-H σ* orbital. This elongates and eventually breaks the X-H bond, leading to characteristic structural, physicochemical characteristics and alteration of the reactivity of the ligand. The requirement for back donation means that the appropriate L n M fragment must usually have appreciable π donor character. Since the binding of the X-H bond to the metal center is relatively weak, and the binding of the deprotonated X À group left behind is much stronger, the binding also facilitates proton loss from the X-H bond. This electron redistribution results in reactivity differences which may be exploited. The case of H 2 is treated in most detail in this review, because of its central place in the field.

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“…Ligands with smaller bite angles yield less bhydrogen elimination products, in contrast with the observed dependence for C-C reductive eliminations. Detailed studies have been performed on amido [221] and alkoxo [222] Ir(I) square-planar complexes, which indicate that reversible phosphine dissociation takes place prior to the b-hydrogen elimination for both amide and alkoxo complexes.…”

Section: Key Intermediates In the Formation Of C-x (X ¼ N O S) Bondmentioning

confidence: 99%

Mechanistic Aspects of Metal‐Catalyzed C—C and C—X Bond‐Forming Reactions

Echavarren

Cárdenas

2005

ChemInform

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Cross-coupling reactions, such as the Stille reaction of organostannanes [1][2][3] and the Suzuki (or Suzuki-Miyaura) cross-coupling of organoboron compounds [4] have settled amongst the more general and selective palladium-catalyzed cross-coupling reactions [5] (Scheme 1-1). These reactions are closely related to other cross-couplings based on transmetallations of a variety of hard or soft organometallic nucleophiles [6] such as the Hiyama [7,8], Sonogashira [9], Kumada (or Kumada-Corriu), and other related couplings [10][11][12].Coupling reactions are somewhat related to the Heck alkenylation of organic electrophiles [13, 14], which is often referred to in the literature as a coupling process. However, although the first steps in both processes are identical, in the Heck reaction there is no transmetallation step. In the alkenylation reaction, the C-C bond is formed by an insertion process, which is followed by a b-hydride elimination to form the substituted alkene product. Cross-coupling (transmetallationbased) processes are a family of closely related catalytic processes that share most mechanistic aspects, although some differences exist on the activation of the organometallic nucleophile. So far, most of the detailed mechanistic studies have cen-

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Directly-Observed β-Hydrogen Elimination of a Late Transition Metal Amido Complex and Unusual Fate of Imine Byproducts

Cited by 79 publications

References 23 publications

Highly Reactive, General and Long-Lived Catalysts for Palladium-Catalyzed Amination of Heteroaryl and Aryl Chlorides, Bromides, and Iodides: Scope and Structure–Activity Relationships

Highly Reactive, General and Long-Lived Catalysts for Palladium-Catalyzed Amination of Heteroaryl and Aryl Chlorides, Bromides, and Iodides: Scope and Structure–Activity Relationships

Sigma Bonds as Ligand Donor Groups in Transition Metal Complexes

Mechanistic Aspects of Metal‐Catalyzed C—C and C—X Bond‐Forming Reactions

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