Copper-promoted reactions in aromatic chemistry

Bacon, R. G. R.; Hill, H. A. O.

doi:10.1039/qr9651900095

Cited by 140 publications

(27 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…R ∑ + Cu 2+ → R + + Cu + ). 55 Therefore, the elucidation of the reaction mechanism for copper-mediated processes often appeared to be cumbersome and has led to conflicting mechanistic proposals, sometimes even for the same reaction.…”

Section: 51mentioning

confidence: 99%

The mechanism of the modified Ullmann reaction

et al. 2010

View full text Add to dashboard Cite

The copper-mediated aromatic nucleophilic substitution reactions developed by Fritz Ullmann and Irma Goldberg required stoichiometric amounts of copper and very high reaction temperatures. Recently, it was found that addition of relatively cheap ligands (diamines, aminoalcohols, diketones, diols) made these reactions truly catalytic, with catalyst amounts as low as 1 mol% or even lower. Since these catalysts are homogeneous, it has opened up the possibility to investigate the mechanism of these modified Ullmann reactions. Most authors agree that Cu(I) is the true catalyst even though Cu(0) and Cu(II) catalysts have also shown to be active. It should be noted however that Cu(I) is capable of reversible disproportionation into Cu(0) and Cu(II). In the first step, the nucleophile displaces the halide in the LnCu(I)X complex forming LnCu(I)ZR (Z = O, NR¢, S). Quite a number of mechanisms have been proposed for the actual reaction of this complex with the aryl halide: 1. Oxidative addition of ArX forming a Cu(III) intermediate followed by reductive elimination; 2. Sigma bond metathesis; in this mechanism copper remains in the Cu(II) oxidation state; 3. Single electron transfer (SET) in which a radical anion of the aryl halide is formed (Cu(I)/Cu(II)); 4. Iodine atom transfer (IAT) to give the aryl radical (Cu(I)/Cu(II)); 5. p-complexation of the aryl halide with the Cu(I) complex, which is thought to enable the nucleophilic substitution reaction. Initially, the radical type mechanisms 3 and 4 where discounted based on the fact that radical clock-type experiments with ortho-allyl aryl halides failed to give the cyclised products. However, a recent DFT study by Houk, Buchwald and co-workers shows that the modified Ullmann reaction between aryl iodide and amines or primary alcohols proceeds either via an SET or an IAT mechanism. Van Koten has shown that stalled aminations can be rejuvenated by the addition of Cu(0), which serves to reduce the formed Cu(II) to Cu(I); this also corroborates a Cu(I)/Cu(II) mechanism. Thus the use of radical clock type experiments in these metal catalysed reactions is not reliable. DFT calculations from Hartwig seem to confirm a Cu(I)/Cu(III) type mechanism for the amidation (Goldberg) reaction, although not all possible mechanisms were calculated.

show abstract

Section: 51mentioning

confidence: 99%

The mechanism of the modified Ullmann reaction

et al. 2010

View full text Add to dashboard Cite

show abstract

“…This associative mechanism for ligand exchange has the advantage that leakage of phenyl radical can explain the benzene which is sometimes observed as a hydrodehalogenation side product (2). Also, cupric copper might further oxidize the phenyl radical to a cation, perhaps accounting for dealkyation in tert-butylated substrates.…”

Section: Intimate Electron Transfer Mechanismmentioning

confidence: 99%

“…Although these reactions have been known for many decades, there has been little systematic investigation of the reaction mechanism (2,6,7). The literature is characterized by questionable conclusions drawn with only a minimum of data, using relative yield measurements, or final product analyses (e.g.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Mechanisms and models for homogeneous copper mediated ligand exchange reactions of the type: CuNu + ArX → ArNu + CuX

Couture¹,

Paine²

1985

Can. J. Chem.

View full text Add to dashboard Cite

C H R I~T I A N ECOUTURE and ANTHONY JAMES PAINE. Can. J. Chem. 63, 1 I 1 (1985). The title reactions arc an important class of copper mediated nucleophilic aromatic substitution processes, which constitute a useful tool in the molecular design and synthesis of small molecules. We report the results of extensive investigation of these processes, primarily focussing on cyanodeiodination (Arl + CuCN + Cul + ArCN). Among the interesting features of these processes are: (a) an unusual rate equation involving autocatalysis by Cul product; (b) retardation by both excess nucleophile (as KCN) and excess leaving group (as KI), which compete with ArX to complex with CuNu; (c) only cuprous nucleophiles are active (ligand exchanged products from cupric salts arise from prior redox equilibria which form CuNu); (d) the halogen effect is large (kl -40-100 kBr -300-5000 kc,) but the Hammett p value is zero; (c) ortho-alkyl groups do not hinder the reaction (and actually cause mild acceleration by relief of steric strain). Finally, the introduction of an ortho-COO group accelerates the reaction by a factor of 10"-lo5, but the general features of the accelerated reactions are also the same, again indicating a common mechanism, with entropic acceleration by ortllo-carboxylatc. Both kinetic and thermodynamic factors were considered in detail, the latter apparently for the first time. Applications to practical syntheses are considered, and novel mechanistic models for these interesting processes are discussed. i la prCsence du groupe carboxylate en ortlzo. On a considire en detail les facteurs cinktiques et therrnodynamiques; il sernble que ces derniers ont Ct C exarnints pour la premiere fois. On considere les applications de ces rkactions dans des syntheses pratiques et on discute de nouveaux modkles rnkcanistiques pour ces reactions intkressantes.[Traduit par Ic journal]

show abstract

Kinetics and mechanism of the nucleophilic exchange reaction of iodide‐131 with 15‐(para‐iodo‐phenyl) pentadecanoic acid

El-Wetery

El-Azoney

Raieh

1997

J Label Compd Radiopharm

View full text Add to dashboard Cite

A procedure for labelling p‐IPPA with 131I by iodine isotope exchange in ethanol using benzoic acid was described. The method results in an overall radiochemical yield of more than 80% within 50 min. at 170°C. The specific activity of the final product was 10 mCi/mg. The reaction conditions were investigated using Cu(I) in acetic acid, pivalic acid, ammonium acetate and ammonium sulfate. The activation energy of the reaction was calculated to be E=33.54 Kcal/mol. Quality control of the product was performed by means of high pressure liquid chromatography HPLC. © 1997 John Wiley & Sons, Ltd.

show abstract

Copper-promoted reactions in aromatic chemistry

Cited by 140 publications

References 1 publication

The mechanism of the modified Ullmann reaction

The mechanism of the modified Ullmann reaction

Mechanisms and models for homogeneous copper mediated ligand exchange reactions of the type: CuNu + ArX → ArNu + CuX

Kinetics and mechanism of the nucleophilic exchange reaction of iodide‐131 with 15‐(para‐iodo‐phenyl) pentadecanoic acid

Contact Info

Product

Resources

About