Alkylpalladium N-Heterocyclic Carbene Complexes: Synthesis, Reactivity, and Catalytic Properties

Esposito, Oriana; Góis, Pedro M. P.; Lewis, Alexandra K. de K.; Caddick, Stephen; Cloke, F. Geoffrey N.; Hitchcock, Peter B.

doi:10.1021/om800455h

Cited by 36 publications

(12 citation statements)

References 55 publications

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“…However, reductive elimination to form an alkyl−nitrogen bond from an isolated Pd complex has not been reported, despite significant effort. 15,16 Thermolysis of 1,1'-Bis(diphenylphosphino)ferrocene (DPPF) ligated alkylpalladium amido complexes that are analogues of the benzylpalladium amido complexes did not generate products from reductive elimination (eq 2). 17 Here, we report a series of isolated and fully characterized three-coordinate Pd-alkylamido complexes ligated by bulky, monodentate N-heterocyclic carbene (NHC) ligands that undergo direct thermal reductive eliminations of N-alkylamines.…”

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confidence: 99%

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

et al. 2012

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A series of three-coordinate norbornylpalladium amido complexes ligated by bulky N-heterocyclic carbene (NHC) ligands were prepared that undergo reductive eliminations to form the alkyl−nitrogen bond of alkylamine products. The rates of reductive elimination reveal that complexes containing more-electron-donating amido groups react faster than those with less-electrondonating amido groups, and complexes containing moresterically bulky amido groups undergo reductive elimination more slowly than complexes containing lesssterically bulky amido groups. Complexes ligated by more-electron-donating ancillary NHC ligands undergo reductive elimination faster than complexes ligated by lesselectron-donating NHC ligands. In contrast to the reductive elimination of benzylamines from bisphosphine-ligated palladium amides, these reactions occur with retention of configuration at the alkyl group, indicating that these reductive eliminations proceed by a concerted pathway. The experimentally determined free energy barrier of 26 kcal/mol is close to the computed free energy barrier of 23.9 kcal/mol (363 K) for a concerted reductive elimination from the isolated, three-coordinate NHC-ligated palladium anilido complex.

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confidence: 99%

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

et al. 2012

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“…6 Reactions of free amines with allyl‐ and benzylpalladium complexes are also known 7–9. However, despite several attempts,10, 11 reductive elimination to form an C(sp 3 )N bond of any type through the simple thermal reaction of an isolated organometallic amido complex has not been reported.…”

Section: Methodsmentioning

confidence: 99%

C(sp³)–N Bond‐Forming Reductive Elimination of Amines: Reactions of Bisphosphine‐Ligated Benzylpalladium(II) Diarylamido Complexes

2010

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Reductive elimination is a common organometallic transformation that is the key product-forming step in many catalytic cycles. [1] Although many examples of reductive elimination from aryl palladium amido complexes to form C(sp 2 ) À N bonds have been reported as part of catalytic processes and as stoichiometric reactions, [2,3] reductive elimination to form a bond between an amide ligand and an sp 3hybridized carbon atom is less common. Reductive elimination from methylplatinum(IV) sulfonamido complexes by dissociation of the sulfonamide has been reported, [4] as has reductive elimination from alkyl nickel amido complexes after the addition of an oxidant. [5,6] Reactions of free amines with allyl-and benzylpalladium complexes are also known. [7][8][9] However, despite several attempts, [10,11] reductive elimination to form an C(sp 3 )ÀN bond of any type through the simple thermal reaction of an isolated organometallic amido complex has not been reported.Herein, we report a purely thermal reductive elimination to form a C(sp 3 ) À N bond in an amine from a benzylpalladium amido complex. An assessment of the stereochemical course of this process showed that it occurs by a stepwise pathway that is distinct from the accepted concerted pathway for the reductive elimination of aromatic amines from aryl palladium(II) species, and an assessment of the effect of the electronic properties of the amido group on the reaction rate showed that this effect is distinct from that observed for reductive elimination to form CÀO bonds from methylplatinum(IV) carboxylate and phenoxide complexes.We prepared a series of benzylpalladium amido complexes to investigate their ability to undergo reductive elimination to form C(sp 3 ) À N bonds without competing bhydrogen elimination. We chose complexes containing chelating ligands to enforce a cis configuration of the benzyl and the amido ligands for reductive elimination; complexes containing a 1,1'-bis(diphenylphosphanyl)ferrocene (dppf) ligand displayed the appropriate balance of stability, reac-tivity, and synthetic accessibility. Dppf-ligated benzylpalladium amido complexes 1-7 were synthesized by treatment of the known complex [(cod)Pd(Bn)Cl] [9] (Bn = benzyl) with dppf followed by the appropriate potassium diarylamide in THF (Scheme 1). Complexes 8 and 9, which contain naphthylmethyl and mesitylmethyl groups, respectively, were synthesized by the treatment of [CpPd(h 3 -allyl)] [12] with dppf followed by naphthylmethyl or mesitylmethyl bromide. The resulting bromide complexes were then converted into the diarylamido complexes by treatment with the appropriate potassium diarylamide. The benzylpalladium arylamido complex 10 and methylpalladium diarylamido complex 11 were synthesized by analogous methods involving the treatment of [(cod)Pd(Bn)Cl] with dppf followed by the potassium anilide, and the treatment of [(cod)Pd(Me)Cl] [13] with dppf followed by the potassium diarylamide. These compounds were characterized by conventional one-and two-dimensional NMR spectroscopic methods and el...

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“…Thus, the first examples of using bulky tertiary phosphines were initially reported by Buchwald and Hartwig, and thenceforth, they have been the most commonly used ligands in aryl amination . Alternatively, N ‐heterocyclic carbenes (NHCs) have also been found considerably beneficial in various cross‐coupling reactions including Buchwald–Hartwig amination . NHCs represent a class of ancillary ligands having paramount importance due to their strong σ‐donor properties .…”

Section: Introductionmentioning

confidence: 99%

Phase‐Separable Polyisobutylene Palladium‐PEPPSI Precatalysts: Synthesis and Application in Buchwald–Hartwig Amination

Balogh

Hlil

El-Zoghbi

et al. 2017

Macromol. Rapid Commun.

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This paper reports the efficient synthesis of the first class of polyisobutylene(PIB)-supported palladium-PEPPSI precatalyst (PEPPSI = pyridine-enhanced precatalyst preparation, stabilization, and initiation). The new complexes are employed in Buchwald-Hartwig amination of aryl chlorides and are found to be reasonably active in the titled cross-coupling reaction. The supported catalysts are tested in polar (1,4-dioxane and 1,2-dimethoxyethane) as well as in aliphatic reaction media (toluene and n-heptane) and display superior activity in the highly lipophilic solvent (n-heptane). The catalytic efficacy of PIB-Pd-PEPPSI precatalyst is measured to be comparable to its nonsupported analog. Pd-leaching is determined by inductively coupled plasma mass spectrometry (ICP-MS) after a simple liquid/liquid extraction and is found to be 2 ppb in the product phase, translating into a recovery of ≈99.8% of the palladium.

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Alkylpalladium N-Heterocyclic Carbene Complexes: Synthesis, Reactivity, and Catalytic Properties

Cited by 36 publications

References 55 publications

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

C(sp³)–N Bond‐Forming Reductive Elimination of Amines: Reactions of Bisphosphine‐Ligated Benzylpalladium(II) Diarylamido Complexes

Phase‐Separable Polyisobutylene Palladium‐PEPPSI Precatalysts: Synthesis and Application in Buchwald–Hartwig Amination

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Alkylpalladium N-Heterocyclic Carbene Complexes: Synthesis, Reactivity, and Catalytic Properties

Cited by 36 publications

References 55 publications

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

Reductive Elimination of Alkylamines from Low-Valent, Alkylpalladium(II) Amido Complexes

C(sp3)–N Bond‐Forming Reductive Elimination of Amines: Reactions of Bisphosphine‐Ligated Benzylpalladium(II) Diarylamido Complexes

Phase‐Separable Polyisobutylene Palladium‐PEPPSI Precatalysts: Synthesis and Application in Buchwald–Hartwig Amination

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C(sp³)–N Bond‐Forming Reductive Elimination of Amines: Reactions of Bisphosphine‐Ligated Benzylpalladium(II) Diarylamido Complexes