Bulky α-diimine palladium complexes: highly efficient for direct C–H bond arylation of heteroarenes under aerobic conditions

Abstract

Through the strategy to enhance the bulkiness on both the backbone and the N-aryl moieties, we designed and synthesized a type of bulky α-diimine palladium complex (i.e., {[Ar-N[double bond, length as m-dash]C(R)-C(R)[double bond, length as m-dash]N-Ar]PdCl2, (Ar = 2-benzhydryl-4,6-dimethylphenyl)}, C1, R = H; C2, R = An; C3, R = Ph). The structures of these palladium complexes were well characterized, while C1 and C3 were further characterized by X-ray diffraction. The catalytic performances of the precatalysts were screened for direct C-H bond arylation of heteroarenes. The bidentate N,N-palladium complex C3 with both a backbone and N-aryl bulkiness was found to be a highly efficient precatalyst under aerobic conditions. With a low palladium loading of 0.5-0.1 mol%, a variety of heteroarenes with challenging bulky steric aryl bromides as well as heteroaryl bromides are all applicable for this cross-coupling reaction.

Dimetallic Palladium‐NHC Complexes: Synthesis, Characterization, and Catalytic Application for Direct C−H Arylation Reaction of Heteroaromatics with Aryl Chlorides

“…The intramolecular non-hydrogen bonding interaction is shown. Selected bond distances and angles (°): Pd1À C1, 1.959(5); Pd1À N7, 2.027(5); Pd1À Cl1, 2.2891 (16) (19); Cl3À Pd2À Cl4, 177.15 (7). Hydrogen atoms are omitted for clarity.…”

“…Only one of the two disordered N-phenyl ring orientations is shown. Selected bond distances and angles (°): Pd1À C1, 1.961(6); Pd1À P1, 2.3268(17); Pd1À Cl1, 2.3268(17); Pd1À N3, 2.109(5); C1À Pd1À P1, 98.42 (16); C1À Pd1À N3, 83.4(2); Cl1À Pd1À N3, 91.77 (16); Cl1À Pd1À P1, 86.86 (7); C1À Pd1À Cl1, 174.03(18); N3À Pd1À P1, 171.59 (16).…”

“…It is worth mentioning that literature reported catalyst systems required the use of more reactive aryl bromides for the preparation of 4 a′′ , 4 b′ , 4 c , 4 d , 4 e′ , 4 f , 4 i , 4 i ′ , 4 k , 4 l , and 4 l′ . The use of chloride analogs as reported herein is unprecedented.…”

Well-Defined Palladium N-Heterocyclic Carbene Complexes: Direct C–H Bond Arylation of Heteroarenes

“…25−28 Notably, extensive studies on bulky and electron-rich phosphine ligands have been carried out over the past few years. In addition, various phosphine-free nitrogen-based ligands, for example, 1,10phenanthroline, 29,30 bipyridyl, 31−33 bulky diamine, 34,35 and others, 36 were used to increase the palladium catalytic efficiency for this type of conversion. However, the efficacy of the reported protocols was limited because of high catalytic loading, very high reaction temperature (up to 150 °C), and long reaction time.…”

Facile Synthesis of Thienopyrroledione-Based π-Conjugated Polymers via Direct Arylation Polycondensation under Aerobic Conditions

“…To avoid catalytic deactivation, the polycondensation reaction must be carried out in an oxygen- and moisture-free environment and thus requires the extra steps of solvent distillation and storage in an inert atmosphere. Alternatively, direct arylation polycondensation using biphasic water/toluene conditions has recently been reported, and some reports of the molecular design and development of robust Pd catalysts for direct arylation in air and water have been published. − These observations prompted our interest in the facile synthesis of π-conjugated polymers via direct arylation under aerobic conditions, which would allow easy handling in air and the use of commercially available reagent-grade solvents, thus avoiding the tedious purification and storage of solvents under an inert atmosphere. As part of an ongoing study of direct sp 2 C–H functionalization strategies toward the synthesis of π-conjugated polymers, this work focuses on exploring the tolerance of Pd-catalyzed direct arylation polycondensation to aerobic reaction conditions.…”