Pyridine Ligands as Promoters in Pd<sup>II/0</sup>-Catalyzed C–H Olefination Reactions

Kubota, Asako; Emmert, Marion H.; Sanford, Melanie S.

doi:10.1021/ol300281p

Cited by 166 publications

(127 citation statements)

References 43 publications

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“…44–49 Empirically, it is observed that heterocycles with higher expected Lewis basicities lead to lower overall product conversion in both C–H oxidation methods, which may be related to coordination-related reduction of reaction rates. Efforts are currently underway to elucidate the heterocycle–Pd(II) speciation as well as to study rates of reaction.…”

Section: Resultsmentioning

confidence: 99%

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Malik¹,

Taylor

Kerrigan³

et al. 2014

Chem. Sci.

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We outline a strategy to enable non-directed Pd(II)-catalyzed C–H functionalization in the presence of Lewis basic heterocycles. In a high-throughput screen of two Pd-catalyzed C–H acetoxylation reactions, addition of a variety of N-containing heterocycles is found to cause low product conversion. A pyridine-containing test substrate is selected as representative of heterocyclic scaffolds that are hypothesized to cause catalyst arrest. We pursue two approaches in parallel that allow product conversion in this representative system: Lewis acids are found to be effective in situ blocking groups for the Lewis basic site, and a pre-formed pyridine N-oxide is shown to enable high yield of allylic C–H acetoxylation. Computational studies with density functional theory (M06) of binding affinities of selected heterocycles to Pd(OAc)2 provide an inverse correlation of the computed heterocycle–Pd(OAc)2 binding affinities with the experimental conversions to products. Additionally, 1H NMR binding studies provide experimental support for theoretical calculations.

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Section: Resultsmentioning

confidence: 99%

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Malik¹,

Taylor

Kerrigan³

et al. 2014

Chem. Sci.

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“…[74] In ähnlicher Weise berichteten auch Sanford und Mitarbeiter kürzlich über den positiven Effekt von Pyridinliganden auf Geschwindigkeit und Selektivität oxidativer Kupplungen zwischen einfachen Arenen und Acrylaten. [75] Anhand von oXylol als Modellsubstrat wurde dabei der Einfluss der Ligandeneigenschaften auf die Regioselektivität der Reaktion gezeigt (Schema 17). Dies demonstriert einmal mehr, wie ein entsprechendes Katalysatordesign nahezu selektive C-HAktivierungen ermçglicht.…”

Section: Methodsunclassified

“…Einfluss von Pyridinliganden auf die Regioselektivität der Olefinierung von o-Xylol. [75] Schema 18. Olefinierung von Brombenzolderivaten von Glorius et al [a] Zur Vereinfachung sind die Ausbeuten der Nebenprodukte nicht angegeben.…”

Section: Carboxylierung Einfacher Areneunclassified

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C‐H‐Aktivierung einfacher Arene

et al. 2012

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Der Einsatz von koordinierenden Gruppen als dirigierende Gruppen ist eine zuverlässige Methode zur Kontrolle von Reaktivität und Selektivität bei der Aktivierung von Aryl‐C‐H‐Bindungen. Im Hinblick auf die Anwendbarkeit von C‐H‐Aktivierungen in der Synthese besteht derzeit ein großes Interesse daran, Reaktionen zu entwickeln, in denen völlig auf dirigierende Gruppen verzichtet werden kann und somit die Funktionalisierung einfacher Benzolderivate möglich wird. Dieser Ansatz erfordert jedoch neue Strategien zur Reaktivitäts‐ und Selektivitätskontrolle. In diesem Kurzaufsatz werden aktuelle Fortschritte in dem noch jungen Gebiet der nicht‐chelatvermittelten C‐H‐Aktivierung diskutiert, wobei einige inspirierende Beispiele zur Reaktivitäts‐ und Selektivitätsinduktion hervorgehoben werden.

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“…Monodentate pyridine derivatives are especially common; 2 however, catalysts containing these ligands are often susceptible to decomposition, especially at elevated temperatures. 3 Catalyst stability can be enhanced through the use of bidentate ligands, such as 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) derivatives. These ligands have been used effectively in Pd-catalyzed aerobic oxidation reactions, although the results are typically observed in polar solvents (e.g., H 2 O, DMSO, DMF) 4 or at high temperatures (120–200 °C), 5 which are often needed to enable anionic ligand dissociation from (N~N)PdX 2 species to access open coordination at the Pd II center.…”

Section: Introductionmentioning

confidence: 99%

Structurally Diverse Diazafluorene-Ligated Palladium(II) Complexes and Their Implications for Aerobic Oxidation Reactions

et al. 2016

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4,5-Diazafluoren-9-one (DAF) has been identified as a highly effective ligand in a number of Pd-catalyzed oxidation reactions, but the mechanistic basis for its utility has not been elucidated. Here, we present the complex coordination chemistry of DAF and palladium(II) carboxylate salts. Multiple complexes among an equilibrating mixture of species have been characterized by 1H and 15N NMR spectroscopy and X-ray crystallography. These complexes include monomeric and dimeric PdII species, with monodentate (κ1), bidentate (κ2) and bridging (μ:κ1:κ1) DAF coordination modes. Titration studies of DAF and Pd(OAc)2 reveal the formation of two dimeric DAF/Pd(OAc)2 complexes at low [DAF] and four monomeric species at higher [DAF]. The dimeric complexes feature two bridging acetate ligands together with either a bridging or non-bridging-κ1 DAF ligand coordinated to each PdII center. The monomeric structures consist of three isomeric Pd(κ1-DAF)2(OAc)2 complexes, together with Pd(κ2-DAF)(OAc)2 in which the DAF exhibits a traditional bidentate coordination mode. Replacing DAF with the structurally related, but more-electron-rich derivative 9,9-dimethyl-4,5-diazafluorene (Me2DAF) simplifies the equilibrium mixture to two complexes, a dimeric species in which the Me2DAF bridges the two Pd centers and a monomeric species with a traditional κ2-Me2DAF coordination mode. The use of DAF in combination with other carboxylate ligands (CF3CO2− or tBuCO2−) also results in a simplified collection of equilibrating PdII–DAF complexes. Collectively, the results highlight the ability of DAF to equilibrate rapidly among multiple coordination modes, and provide valuable insights into the utility of DAF as a ligand in Pd-catalyzed oxidation reactions.

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Pyridine Ligands as Promoters in Pd^II/0-Catalyzed C–H Olefination Reactions

Abstract: Commercially available pyridine ligands can significantly enhance the rate, yield, substrate scope, and site selectivity of arene C-H olefination (Fujiwara-Moritani) reactions. The use of a 1:1 ratio of Pd/pyridine proved critical to maximize reaction rates and yields.

Cited by 166 publications

References 43 publications

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C‐H‐Aktivierung einfacher Arene

Structurally Diverse Diazafluorene-Ligated Palladium(II) Complexes and Their Implications for Aerobic Oxidation Reactions

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Pyridine Ligands as Promoters in PdII/0-Catalyzed C–H Olefination Reactions

Abstract: Commercially available pyridine ligands can significantly enhance the rate, yield, substrate scope, and site selectivity of arene C-H olefination (Fujiwara-Moritani) reactions. The use of a 1:1 ratio of Pd/pyridine proved critical to maximize reaction rates and yields.

Cited by 166 publications

References 43 publications

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C‐H‐Aktivierung einfacher Arene

Structurally Diverse Diazafluorene-Ligated Palladium(II) Complexes and Their Implications for Aerobic Oxidation Reactions

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Product

Resources

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Pyridine Ligands as Promoters in Pd^II/0-Catalyzed C–H Olefination Reactions