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1. Suzuki–Miyaura cross-coupling of esters by selective O–C(O) cleavage mediated by air- and moisture-stable [Pd(NHC)(μ-Cl)Cl] 2 precatalysts: catalyst evaluation and mechanism

   https://doi.org/10.1039/D1CY00312G  

   Yang, Shiyi ; Zhou, Tongliang ; Poater, Albert ; Cavallo, Luigi ; Nolan, Steven P. ; Szostak, Michal ( January 2021 , Catalysis Science & Technology)

   null (Ed.)

   The cross-coupling of aryl esters has emerged as a powerful platform for the functionalization of otherwise inert acyl C–O bonds in chemical synthesis and catalysis. Herein, we report a combined experimental and computational study on the acyl Suzuki–Miyaura cross-coupling of aryl esters mediated by well-defined, air- and moisture-stable Pd( ii )–NHC precatalysts [Pd(NHC)(μ-Cl)Cl] 2 . We present a comprehensive evaluation of [Pd(NHC)(μ-Cl)Cl] 2 precatalysts and compare them with the present state-of-the-art [(Pd(NHC)allyl] precatalysts bearing allyl-type throw-away ligands. Most importantly, the study reveals [Pd(NHC)(μ-Cl)Cl] 2 as the most reactive precatalysts discovered to date in this reactivity manifold. The unique synthetic utility of this unconventional O–C(O) cross-coupling is highlighted in the late-stage functionalization of pharmaceuticals and sequential chemoselective cross-coupling, providing access to valuable ketone products by a catalytic mechanism involving Pd insertion into the aryl ester bond. Furthermore, we present a comprehensive study of the catalytic cycle by DFT methods. Considering the clear advantages of [Pd(NHC)(μ-Cl)Cl] 2 precatalysts on several levels, including facile one-pot synthesis, superior atom-economic profile to all other Pd( ii )–NHC catalysts, and versatile reactivity, these should be considered as the ‘first-choice’ catalysts for all routine applications in ester O–C(O) bond activation. 

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2. Sonogashira Cross-Coupling of Aryl Ammonium Salts by Selective C–N Activation Catalyzed by Air- and Moisture-Stable, Highly Active [Pd(NHC)(3-CF 3 -An)Cl 2 ] (An = Aniline) Precatalysts

   https://doi.org/10.1021/acs.orglett.2c02534  

   Lei, Peng ; Wang, Yibo ; Zhang, Caixia ; Hu, Yuge ; Feng, Juntao ; Ma, Zhiqing ; Liu, Xili ; Szostak, Roman ; Szostak, Michal ( September 2022 , Organic Letters)
3. [Pd(NHC)(acac)Cl]: Well-Defined, Air-Stable, and Readily Available Precatalysts for Suzuki and Buchwald–Hartwig Cross-coupling (Transamidation) of Amides and Esters by N–C/O–C Activation

   https://doi.org/10.1021/acs.orglett.9b01053  

   Zhou, Tongliang ; Li, Guangchen ; Nolan, Steven P. ; Szostak, Michal ( April 2019 , Organic Letters)
4. Buchwald–Hartwig cross-coupling of amides (transamidation) by selective N–C(O) cleavage mediated by air- and moisture-stable [Pd(NHC)(allyl)Cl] precatalysts: catalyst evaluation and mechanism

   https://doi.org/10.1039/C9CY02080B  

   Li, Guangchen ; Zhou, Tongliang ; Poater, Albert ; Cavallo, Luigi ; Nolan, Steven P. ; Szostak, Michal ( February 2020 , Catalysis Science & Technology)

   The Pd–NHC-catalyzed acyl-type Buchwald–Hartwig cross-coupling of amides by N–C(O) cleavage (transamidation) provides a valuable alternative to the classical methods for amide synthesis. Herein, we report a combined experimental and computational study of the Buchwald–Hartwig cross-coupling of amides using well-defined, air- and moisture-stable [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, we present a comprehensive evaluation of a series of distinct Pd( ii )–NHC precatalysts featuring different NHC scaffolds and throw-away ligands for the synthesis of functionalized amides that are not compatible with stoichiometric transition-metal-free transamidation methods. Furthermore, we present evaluation of the catalytic cycle by DFT methods for a series of different Pd( ii )–NHC precatalysts. The viability of accessing NHC-supported acyl-palladium( ii ) amido complexes will have implications for the design and development of cross-coupling methods involving stable amide electrophiles. 

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5. Suzuki‐Miyaura Cross‐Coupling of Amides using Well‐Defined, Air‐Stable [(PR 3 ) 2 Pd(II)X 2 ] Precatalysts

   https://doi.org/10.1002/adsc.202000122  

   Ma, Siyue ; Zhou, Tongliang ; Li, Guangchen ; Szostak, Michal ( April 2020 , Advanced Synthesis & Catalysis)

   A versatile method for the Suzuki‐Miyaura cross‐coupling of amides using highly active, well‐defined, and air‐stable Pd−phosphine precatalysts is reported. Most notably, the method represents the first example of using practical and operationally‐simple Pd(II)−phosphine precatalysts in the emerging amide bond cross‐coupling manifold. The reactions are efficient at 0.10 mol% loading, furnishing biaryl ketones with high chemoselectivity for N−C(O) bond cleavage. This versatile method enables for the first time to achieve Pd−phosphine‐catalyzed cross‐coupling of amides at ppm loading. This C−N cross‐coupling can be used to efficiently furnish pharmaceutical intermediates by orthogonal Pd‐catalyzed cross‐couplings. We fully expect that operationally‐simple [(PR₃)₂Pd(II)X₂] precatalysts as effective triggers for N−C(O) cross‐coupling will be of broad synthetic and catalytic interest.

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