[(NHC)PdCl₂(Aniline)] Complexes: Easily Synthesized, Highly Active Pd(II)–NHC Precatalysts for Cross-Coupling Reactions

Abstract

We report the synthesis, characterization, and reactivity of [(NHC)PdCl 2 (aniline)] complexes. These well-defined, air-and moisture-stable catalysts are highly active in the Suzuki−Miyaura cross-coupling of amides by N−C(O) activation as well as in the Suzuki−Miyaura cross-coupling of esters, aryl chlorides, and Buchwald−Hartwig amination. Most crucially, this study introduces broadly available anilines as stabilizing ligands for well-defined Pd(II)−NHC catalysts. The availability of various aniline scaffolds, including structural and electronic diversity, has a significant potential in fine-tuning of challenging cross-couplings by Pd− NHCs. The parent catalyst in this class, [Pd(IPr)(AN)Cl 2 ], has been commercialized in collaboration with Millipore Sigma, offering broad access for reaction screening and optimization.

Recent Development in the Catalytic Applications of Pd‐NHC (NHC=N‐Heterocyclic Carbene) Compounds in Amide C−N Activation Reactions

“…[52] And, Szostak reported the synthesis, characterization, and reactivity of [Pd (NHC) (aniline) Cl 2 ] complexes. [53]…”

“…Stabilizing effect of amine nitrogen to palladium is a key feature in the formation of palladium rings. [65] So, the Szostak's group used the amine-type nitrogen-aniline ligands to create Pd(II)-(NHC)Cl 2 (Aniline) catalyst [53] The effect of substituents on aniline on catalytic activity was also studied in detail by using a series of electronically and sterically differentiated precatalysts that demonstrated high reactivity in the Suzuki-Miyaura cross-coupling of amides by CÀ N(O) activation at mild room temperature. The Pd-NHC catalyst bearing 3-trifluoromethylaniline was more efficient than the neutral aniline ligand in the more challenging crosscoupling reactions.…”

“…[66] Currently, this catalyst is the easiest to synthesize from the corresponding NHC salts. [53,67] And the use of acac throw-away ligand permited to in situscreen NHC salts in this cross-coupling manifold (Scheme 25), which was not possible with any other throwaway ligands. Different substituents on amide N atom are compatible, but the reaction temperature was higher.…”

Bis(imino)acenaphthene (BIAN)-Supported N-Heterocyclic Carbene Palladium Complexes with Ancillary Ligands: Readily Activated Precatalysts for Direct C–H Arylation of Thiophenes

“…We noticed that the bulky bis­(imino)­acenaphthene-supported N -heterocyclic carbene (BIAN-IPr) metal complexes have been proved to be highly active in C–C, C–N, and direct C–H arylation cross-couplings, which suggest that the structural feature might perform excellent properties in the catalytic process of the direct arylation reactions . Besides the dominant NHC ligand, the so-called “throw-away” ancillary ligand, which is involved in the steps of the catalyst activation, is another important aspect of the whole catalyst reactivity. , In order to gain more information about this catalytic process, we herein report the synthesis and characterization of the BIAN-IPr palladium complexes bearing a series of monodentate ancillary ligands.…”

N‐Heterocyclic Carbene Palladium(II) Amine Complexes: The Role of Primary Aryl‐ or Alkylamine Binding and Applications in the Buchwald‐Hartwig Amination Reaction

“…Recently, the Szostak group also has successfully contributed in the Suzuki-Miyaura cross-coupling of amides by NÀ C(O) activation as well as of esters and aryl chlorides. [22] In the connection, we targeted that tuning of stereoelectronic structures of primary amines accompanied with the NHC ligand is the idea in their implementation in this challenging catalytic reaction. In this study, we wanted to extend the cross-coupling application in the presence of aryl chlorides as substrates for Buchwald-Hartwig amination reaction under mild controlled conditions.…”