Pincer Complex-Catalyzed Redox Coupling of Alkenes with Iodonium Salts via Presumed Palladium(IV) Intermediates

Aydin, Juhanes; Larsson, Johanna M.; Selander, Nicklas; Szabó, Kálmán J.

doi:10.1021/ol9010739

Cited by 88 publications

(39 citation statements)

References 37 publications

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“…[22] However, subsequent halide dissociation, coordination of styrene (in cis position relative to the phenyl ligand), and migration of the phenyl ligand to the olefinic bond would yield the cationic, pentacoordinate 1,2-diphenylethyl complexes, which could undergo b-hydride elimination and liberate (E)-stilbene, for example, to give cationic hydride + . The catalytic cycle could be closed after their deprotonation (Scheme 1).…”

Section: Resultsmentioning

confidence: 99%

“…with the metal center in the oxidation state of + IV, similar to the recently reported coupling of alkenes with iodonium salts, for which the involvement of six-coordinate Pd IV intermediates was postulated (and supported by DFT calculations). [22] However, subsequent halide dissociation, coordination of styrene (in cis position relative to the phenyl ligand), and migration of the phenyl ligand to the olefinic bond would yield the cationic, pentacoordinate 1,2-diphenylethyl complexes, which could undergo b-hydride elimination and liberate (E)-stilbene, for example, to give cationic hydride The catalytic cycle could be closed after their deprotonation (Scheme 1). [23] The oxidative addition of phenyl bromide to 1 a to yield 3 a is initiated by a Pd-Br interaction, leading to a three-centered transition state TS 1 a/3 a with distorted trigonal-bipyramidal geometry around the metal center ( Figure 2).…”

Section: Resultsmentioning

confidence: 99%

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Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study

Blacque

Frech

2010

Chemistry A European J

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Pincer-type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain Pd(II) centers, controversial Pd(II)/Pd(IV) cycles have been often proposed as potential catalytic mechanisms. However, pincer-type Pd(IV) intermediates have never been experimentally observed, and computational studies to support the proposed Pd(II)/Pd(IV) mechanisms with pincer-type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving Pd(IV) intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine-, phosphine-, and phosphite-based pincer-type Heck catalysts with styrene and phenyl bromide as substrates and (E)-stilbene as coupling product. The potential-energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that Pd(II)/Pd(IV) mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6-C(6)H(3)(XPR(2))(2)}Pd(Cl)] [X=NH, R=piperidinyl (1 a); X=O, R=piperidinyl (1 b); X=O, R=iPr (1 c); X=CH(2), R=iPr (1 d)] to yield cationic, three-coordinate, T-shaped 14e(-) palladium intermediates of type [{2,6-C(6)H(3)(XPR(2))(2)}Pd](+) (2). An alternative reaction path to generate complexes of type 2 (relevant for electron-poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6-C(6)H(3)(XPR(2))(2)}Pd(Cl)(CH(2)=CHPh)] (4) and consecutive dissociation of the chloride ligand to yield cationic square-planar styrene complexes [{2,6-C(6)H(3)(XPR(2))(2)}Pd(CH(2)=CHPh)](+) (6) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate Pd(IV) complexes of type [{2,6-C(6)H(3)(XPR(2))(2)}Pd(Br)(C(6)H(5))](+) (11), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6-C(6)H(3)(XPR(2))(2)}Pd(Br)(C(6)H(5))(CH(2)=CHPh)](+) (12). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6-C(6)H(3)(XPR(2))(2)}Pd(Br)(CHPhCH(2)Ph)](+) (13). Subsequent beta-hydride elimination induces direct HBr liberation to yield cationic, square-planar (E)-stilbene complexes with general formula [{2,6-C(6)H(3)(XPR(2))(2)}Pd(CHPh=CHPh)](+) (14). Subsequent liberation of (E)-stilbene closes the catalytic cycle.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study

Blacque

Frech

2010

Chemistry A European J

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“…[129] Szabó and co-workers used palladium pincer complexes in the coupling of alkenes with diaryliodonium triflates, which enabled the development of a mild method for the arylation of allylic acetates and electron-rich alkenes (Scheme 31). [130] The reaction was proposed to proceed by a Pd II /Pd IV catalytic cycle, and palladium acetate was also found to be an efficient catalyst for the transformation.…”

Section: Arylation Of Alkenesmentioning

confidence: 99%

Diaryliodonium Salts: A Journey from Obscurity to Fame

2009

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The recent groundbreaking developments in the application of diaryliodonium salts in cross-coupling reactions has brought this class of previously underdeveloped reagents to the forefront of organic chemistry. With the advent of novel, facile, and efficient synthetic routes to these compounds, many more applications can be foreseen. Herein we provide an overview of the historical and recent advances in the synthesis and applications of diaryliodonium salts.

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“…[129] Szabó und Mitarbeiter setzten Palladium-Pinzettenkomplexe in der Kupplung von Alkenen mit Diaryliodoniumtriflaten ein und erhielten so eine milde Methode zur Arylierung von Allylacetaten und elektronenreichen Alkenen (Schema 31). [130] [118] Auch eine Kupfer-katalysierte Variante dieser Reaktion ist bekannt, [114] ebenso wie eine nicht-carbonylierende Stille-Kupplung. [131] 1996 veröffentlichten Kang et al eine Suzuki-Kreuzkupplung mit Vinylboranen in Gegenwart von nur 0.2 Mol-% [Pd(PPh 3 ) 4 ] als Katalysator, die das gewünschte Produkt in nur 10 min bei Raumtemperatur lieferte (Schema 33).…”

Section: Arylierung Von Alkenenunclassified

“…[129] Szabó und Mitarbeiter setzten Palladium-Pinzettenkomplexe in der Kupplung von Alkenen mit Diaryliodoniumtriflaten ein und erhielten so eine milde Methode zur Arylierung von Allylacetaten und elektronenreichen Alkenen (Schema 31). [130] Für den Reaktionsverlauf wurde ein Pd II / Schema 26. Pd/Ag-katalysierte Sonogashira-Reaktion.…”

Section: Arylierung Von Alkenenunclassified

Diaryliodoniumsalze – aus dem Nichts ins Rampenlicht

2009

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Die jüngsten bahnbrechenden Entwicklungen bei der Anwendung von Diaryliodoniumsalzen in Kreuzkupplungsreaktionen haben diese ehemals unterentwickelte Klasse von Reagentien in die vorderste Reihe der organischen Chemie katapultiert. Mit dem Aufkommen neuartiger, einfacher, effizienter Methoden zur Synthese dieser Reagentien lassen sich noch sehr viel mehr Einsatzmöglichkeiten voraussehen. Wir bieten hier einen Überblick über die historischen und neuerlichen Fortschritte bei der Synthese und Anwendung von Diaryliodoniumsalzen.

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Pincer Complex-Catalyzed Redox Coupling of Alkenes with Iodonium Salts via Presumed Palladium(IV) Intermediates

Cited by 88 publications

References 37 publications

Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study

Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study

Diaryliodonium Salts: A Journey from Obscurity to Fame

Diaryliodoniumsalze – aus dem Nichts ins Rampenlicht

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Pincer Complex-Catalyzed Redox Coupling of Alkenes with Iodonium Salts via Presumed Palladium(IV) Intermediates

Cited by 88 publications

References 37 publications

Pincer‐Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational Study

Pincer‐Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational Study

Diaryliodonium Salts: A Journey from Obscurity to Fame

Diaryliodoniumsalze – aus dem Nichts ins Rampenlicht

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Product

Resources

About

Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study

Pincer‐Type Heck Catalysts and Mechanisms Based on Pd^IV Intermediates: A Computational Study