N-Heterocyclic Carbene–Palladium(II)–4,5-Dihydrooxazole Complexes: Synthesis and Catalytic Activity toward Amination of Aryl Chlorides

Crystal structure of a three-coordinate lithium complex with monodentate phenyl-oxazoline and hexa-methyl-disilyl-amide ligands

The reaction of lithium hexa-methyl-disilyl-amide, [Li{N(Si(CH3)3)2}] (LiHMDS), with 4,4-dimethyl-2-phenyl-2-oxazoline (Phox, C11H13NO) in hexane produced colourless crystals of bis-(4,4-dimethyl-2-phenyl-2-oxazoline-κN)(hexa-methyl-disilyl-amido-κN)lithium, [Li(C6H18NSi2)(C11H13NO)2] or [Li{N(Si(CH3)3)2}(Phox)2] in high yield (89%). Despite the 1:1 proportion of the starting materials in the reaction mixture, the product formed with a 1:2 amide:oxazoline ratio. In the unit cell of the C2/c space group, the neutral mol-ecules lie on twofold rotation axes coinciding with the Li-N(amide) bonds. The lithium(I) centre adopts a trigonal-planar coordination geometry with three nitro-gen donor atoms, one from the HMDS anion and two from the oxazolines. All ligands are monodentate. In the phenyl-oxazoline units, the dihedral angle defined by the five-membered heterocyclic rings is 35.81 (5)°, while the phenyl substituents are approximately face-to-face, separated by 3.908 (5) Å. In the amide, the methyl groups assume a nearly eclipsed arrangement to minimize steric repulsion with the analogous substituents on the oxazoline rings. The non-covalent inter-actions in the solid-state structure of [Li{N(Si(CH3)3)2}(Phox)2] were assessed by Hirshfeld surface analysis and fingerprint plots. This new compound is attractive for catalysis due to its unique structural features.

Palladium N-Heterocyclic Carbene-Catalyzed Aminations: An Outline

Amination reactions play a pivotal role in synthetic organic chemistry, facilitating the generation of nitrogen-containing scaffolds with broad applications in drug synthesis, material production, polymer formation, and the generation of amino acids and peptides. Amination offers the potential to fine tune the properties of natural products and produce functional materials for various applications. Palladium N-heterocyclic carbene (Pd-NHC) emerges as an innovative and highly effective catalyst in this context. Under favorable reaction conditions, this robust and simple catalyst efficiently facilitates the synthesis of a diverse range of compounds with varying complexity and utility. Pd-NHC complexes exhibit significant σ-electron donating potential, enhancing the ease of the oxidative addition process in their mechanistic pathway. Their steric topography further contributes to a rapid reductive elimination. These complexes demonstrate remarkable stability, a result of the strong Pd-ligand bond. The wide variety of Pd-NHC complexes has proven highly efficient in catalyzing reactions across a spectrum of complexities, from simple to intricate. The domain of aminations catalyzed by Pd-NHC has undergone significant diversification, presenting new opportunities, particularly in the realms of material chemistry and natural product synthesis. This review outlines the advancements in Pd-NHC-catalyzed amination reactions, covering literature up to date.

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

We report the synthesis, characterization, and reactivity of [(NHC)PdCl2(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)Cl2], has been commercialized in collaboration with Millipore Sigma, offering broad access for reaction screening and optimization.

Understanding existing and designing novel synthetic routes to Pd-PEPPSI-NHC and Pd-PEPPSI-PR3 pre-catalysts

The reaction mechanism leading to the formation of cross-coupling palladium pre-catalysts of the PEPPSI family was investigated. Two intermediates were isolated and proved to be both suitable synthons to the pre-catalysts, with one permitting the design of a novel and greener user-friendly synthetic route. In light of this mechanistic understanding, the traditional one-pot method was shown to be possible using stoichiometric amounts of throw-away ligand, which represents a considerable synthetic improvement over the wasteful "in pyridine" approach.

The crystal structure of tetrachlorido-bis{1,3-bis(2,6-diisopropylphenyl)-1H-3λ4-imidazol-2-yl}-(μ2-pyrimidine-κ2N:N′)dipalladium(IV) — dichloromethane (1/2), C60H80Cl8N6Pd2

C60H80Cl8N6Pd2, triclinic, P1̄ (no. 2), a = 10.8703(10) Å, b = 17.0284(15) Å, c = 18.9595(17) Å, α = 83.1960(10)°, β = 88.909(2)°, γ = 71.523(2)°, V = 3304.5(5) Å3, Z = 2, Rgt(F) = 0.0488, wRref(F2) = 0.1213, T = 130 K.

The crystal structure of dichlorido(1,3-bis(2,6-diisopropyl-phenyl)-1H-3λ4-imidazol-2-yl)(3-phenyl-pyridine-κN)palladium(IV), C38H45N3Cl2Pd

C38H45N3Cl2Pd, monoclinic, P21/c (no. 14), a = 12.8249(8) Å, b = 16.0552(9) Å, c = 20.5611(10) Å, β = 115.396(3)°, V = 3824.5(4) Å3, Z = 4, R gt(F) = 0.0287, wR ref(F 2) = 0.0879, T = 173(2) K.

Rigid hindered N-heterocyclic carbene palladium precatalysts: synthesis, characterization and catalytic amination

Rigid hindered N-heterocyclic carbene palladium complexes have been developed and exhibited high activities for a variety of (hetero)aryl chlorides with (hetero)anilines and amines under aerobic conditions.

The crystal structure of dichlorido-(1,3-bis(2,6-dimethylphenyl)-1H-imidazol-2(3H)-ylidene)-(morpholine-κ1 N)palladium(II), C23H29Cl2N3OPd(II)

C23H29Cl2N3OPd, monoclinic, P21/c (no. 14), a = 9.6053(2) Å, b = 17.4544(4) Å, c = 14.5156(3) Å, β = 104.6440(10)°, V = 2354.55(9) Å3, Z = 4, R gt(F) = 0.0184, wR ref(F 2) = 0.0455, T = 173(2) K.

Highly active NHC–Pd(ii) complexes for cross coupling of aryl chlorides and arylboronic acids: an investigation of the effect of remote bulky groups

Highly active palladium(ii) complexes bearing remote bulky ligands for Suzuki–Miyaura coupling reactions under mild conditions are reported.

Effect on orthometallation of NHC palladium complexes toward the catalytic activity studies in Suzuki coupling reaction

Herein, we report an approach to improve catalytic activity for cross-coupling reactions.

Crystal structure of dichlorido(1,3-bis(2,6-dimethyl-phenyl)-1H-3λ4-imidazol-2-yl)(isoquinolinyl)palladium(IV), C28H27Cl2N3Pd

C28H27Cl2N3Pd, monoclinic (no. 15), C2/c, a = 24.7394(17) Å, b = 15.9451(11) Å, c = 27.4301(19) Å, β = 107.8650°, V = 10293.7(12) Å3, Z = 16, R gt(F) = 0.0249, wR ref(F 2) = 0.1168, T = 100(2) K.

Synthesis and characterization of trinuclear N-heterocyclic carbene–palladium(ii) complexes and their applications in the Suzuki–Miyaura cross-coupling reaction

Five novel trinuclear N-heterocyclic carbene–palladium(ii) complexes 5a–e were conveniently synthesized in one step. The obtained palladium(ii) complexes were the effective catalyst precursors for the Suzuki–Miyaura coupling.

Synthesis and characterization of N-heterocyclic carbene-palladium(ii) chlorides-1-methylindazole and -1-methylpyrazole complexes and their catalytic activity toward C–N coupling of aryl chlorides

N-heterocyclic carbene-palladium(ii) chlorides-1-methylindazole and -1-methylpyrazole complexes were successfully synthesized and characterized. Investigations showed that they were efficient catalysts in amine coupling with aryl chlorides at low catalyst loadings.

Mono- and dinuclear palladium(ii) complexes containing both N-heterocyclic carbenes and tetrazole ligands as catalysts for Hiyama coupling

Six tetrazole ligand stabilized NHC–Pd complexes have been synthesized and fully characterized. Catalytic performance of the obtained palladium catalysts has been investigated for the Hiyama coupling reaction.

Synthesis of N-heterocyclic carbene–PdCl2–(iso)quinoline complexes and their application in arylamination at low catalyst loadings

N-Heterocyclic carbene–PdCl₂–(iso)quinoline complexes were synthesized and they showed efficient catalytic activity in the C–N coupling of aryl chlorides.

Effective, transition metal free and selective C–F activation under mild conditions

A simple and effective aromatic nucleophilic monosubstitution reaction for the synthesis of aromatic amines via selective C–F bond cleavage of various fluoroarenes with primary and secondary aromatic amines is demonstrated.

A new library of arsine, stibine-stabilized N-heterocyclic carbene palladium complexes: synthesis, structures and activities in C-C and C-N coupling reactions

A series of new N-heterocyclic carbene palladium complexes bearing AsPh3 and SbPh3 functions PdCl2(IMes)(AsPh3) (1a), PdCl2(IMes)(SbPh3) (1b), PdCl2(IPr)(AsPh3) (1c), PdCl2(IPr)(SbPh3) (1d), PdCl2(SIMes)(AsPh3) (2a), PdCl2(SIMes)(SbPh3) (2b), PdCl2(SIPr)(AsPh3) (2c), and PdCl2(SIPr)(SbPh3) (2d) (IMes = N,N'-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene; IPr = N,N'-bis-(2,6-di(iso-propyl)phenyl)imidazol-2-ylidene; SIMes = N,N'-bis-(2,4,6-trimethylphenyl)imidazolidin-2-ylidene; SIPr = N,N'-bis-(2,6-di(iso-propyl)phenyl)imidazolidin-2-ylidene) was synthesized and fully characterized by (1)H NMR, (13)C NMR, and FT-IR spectroscopy, elemental analysis and single-crystal X-ray crystallography. The catalytic potential of these arsine and stibine-stabilized carbene palladium complexes for Pd-mediated transformations was investigated with various substrates in the Hiyama cross-coupling reactions and Buchwald-Hartwig aminations. The results demonstrate that these complexes show high catalytic activity and good tolerance to various chemical functions.