Competition between sp3-C–N vs sp3-C–F Reductive Elimination from PdIV Complexes

Pérez‐Temprano, Mónica H.; Racowski, Joy M.; Kampf, Jeff W.; Sanford, Melanie S.

doi:10.1021/ja411433f

Cited by 96 publications

(69 citation statements)

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“…It has been shown by Doyle and coworkers that Pd-bound fluoride species can act as nucleophile in Pd-catalyzed allylic fluorination 38 . Indeed, our mechanistic hypothesis of the competitive nature of C(sp 3 )–Pd(IV) reductive elimination mechanism (S N 2 vs. inner-sphere) is supported by a number of previous kinetic and computational studies 32,33,39–41 . It is intriguing that under our system the ratio of C(sp 3 )–O vs. C(sp 3 )–F can serve as a measurement for the competition between the inner-sphere reductive elimination and S N 2 pathway from Pd(IV) intermediate during catalysis.…”

Section: Resultssupporting

confidence: 65%

“…The major pitfall of C(sp 3 )–H fluorination using Pd(II/IV) catalysis is the relatively sluggish C–F reductive elimination from Pd(IV) species, which renders [F + ] a broadly useful bystanding oxidant that favors the reductive elimination of other C(sp 3 )–C(sp 3 ) or C(sp 3 )–heteroatom bonds (Figure 1a) 29–31 . In addition, C(sp 3 )–[Pd(IV)(L n )]–F species have been proposed to undergo S N 2-type reactions with various oxygen- and nitrogen-nucleophiles, forming C(sp 3 )–O and C(sp 3 )–N bonds instead of C(sp 3 )–F bond 32–34 . These observations call into the question whether such reductive elimination selectivity could be biased towards fluorination by modifying the ligand environment of a Pd(IV)–F intermediate.…”

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confidence: 99%

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Controlling Pd(iv) reductive elimination pathways enables Pd(ii)-catalysed enantioselective C(sp3)−H fluorination

et al. 2018

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The development of a Pd(II)-catalyzed enantioselective fluorination of C(sp3)–H bonds would offer a new approach to making chiral organofluorines. However, such a strategy is particularly challenging because of the difficulty in differentiating prochiral C(sp3)–H bonds through Pd(II)-insertion, as well as the sluggish reductive elimination involving Pd–F bonds. Here, we report the development of a Pd(II)-catalyzed enantioselective C(sp3)–H fluorination using a chiral transient directing group strategy. In this work, a bulky, amino amide transient directing group was developed to control the stereochemistry of C–H insertion step and selectively promote C(sp3)–F reductive elimination pathway from Pd(IV)–F intermediate. Stereochemical analysis revealed that while the desired C(sp3)–F formation proceeds via an inner-sphere pathway with retention of configuration, the undesired C(sp3)–O formation occurs through an SN2-type mechanism. The elucidation of the dual mechanism allows us to rationalize the profound ligand effect on controlling reductive elimination selectivity from high-valent Pd species.

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confidence: 65%

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confidence: 99%

Controlling Pd(iv) reductive elimination pathways enables Pd(ii)-catalysed enantioselective C(sp3)−H fluorination

et al. 2018

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“…This hypothesis was based on literature investigations of the reactivity of Ni II (18)(19)(20) and Pd II (21,22) analogs of 1, as well as on cyclic voltammetry studies carried out in our lab. As shown in Fig.…”

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confidence: 99%

“…(16,21,22). We anticipated that these Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes oxidants would react with 1 to generate coordinatively saturated, diamagnetic Ni IV intermediates of general structure 2 (X = F/OTf, OAc, or Cl).…”

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confidence: 99%

“…Products derived from competing C(sp 2 )-C(sp 3 ) coupling or C(sp 2 )-heteroatom coupling were not detected in the 1 H NMR spectra of the crude reaction mixtures. Notably, C(sp 3 )-heteroatom coupling reactions of this type are rare in organometallic chemistry (20)(21)(22)(30)(31)(32)(33)(34), and most previously reported examples involve second or third row metal centers. In addition, the observation of selective C(sp 3 )-heteroatom coupling is complementary to the reactivity of other oxidation states of Ni, where C(sp 2 )-heteroatom bond-formation has significant precedent (35)(36)(37).…”

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Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes

Camasso

Sanford

2015

Science

Self Cite

267

182

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Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni(0), Ni(I), Ni(II), and/or Ni(III) oxidation states. In contrast, Ni(IV) intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic Ni(IV) complexes, accessed by the reaction of Ni(II) precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These Ni(IV) complexes undergo highly selective carbon(sp(3))-oxygen, carbon(sp(3))-nitrogen, and carbon(sp(3))-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions.

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Transition‐Metal‐Mediated and Transition‐Metal‐Catalyzed Carbon–Fluorine Bond Formation

Neumann

Ritter

2020

Organic Reactions

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The number and diversity of methods for installing carbon–fluorine bonds have substantially expanded over the past two decades, enabling enantioselective fluorinations, reactions with complex substrates, and the use of ever simpler reaction precursors. Fluorination chemistry was long held back by unreactive alkali fluoride salts and highly reactive electrophilic fluorine sources, such as molecular fluorine and cobalt(III) fluoride. The introduction of fluorination reagents with controlled reactivity has been a key driving force in harnessing the reactivity of fluoride, as has the strategic use of transition metals. These approaches enable predictable and functional‐group‐tolerant carbon–fluorine bond formation. Herein, transition‐metal‐catalyzed and transition‐metal‐mediated syntheses of aromatic, heteroaromatic, and alkyl fluorides are reviewed. In addition, methods for allylic fluorination, benzylic fluorination, and fluorination α to carbonyl groups are presented. The influence of these reactions on the synthesis of complex fluorinated molecules and the preparation of 18 F‐PET probes are described, and experimental procedures for illustrative examples are included.

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Competition between sp³-C–N vs sp³-C–F Reductive Elimination from Pd^IV Complexes

Cited by 96 publications

References 44 publications

Controlling Pd(iv) reductive elimination pathways enables Pd(ii)-catalysed enantioselective C(sp3)−H fluorination

Controlling Pd(iv) reductive elimination pathways enables Pd(ii)-catalysed enantioselective C(sp3)−H fluorination

Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel(IV) complexes

Transition‐Metal‐Mediated and Transition‐Metal‐Catalyzed Carbon–Fluorine Bond Formation

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