Synthesis and Structure of Imine–N-Heterocyclic Carbene Palladium Complexes and Their Catalytic Behavior in Norbornene Polymerization

Abstract

On the basis of the steric effects of ligand, a series of imine–N-heterocyclic carbene (NHC) ligands and their corresponding five-membered palladium complexes with bulky substituents on both the imine and the NHC moieties were synthesized and characterized. Transpalladation of silver carbene complexes with (COD)­PdCl2 and (COD)­PdMeCl afforded the palladium dichloride and methylpalladium complexes, respectively. Bulky cationic palladium complexes were further obtained by treatment of the methylpalladium complexes with sodium tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate (NaBAF) in CH3CN. Well-defined cationic palladium complexes were confirmed by X-ray crystal diffraction to have trans forms. Palladium dichloride complexes and methylpalladium complexes after activation with MMAO show high activity for norbornene polymerization, whereas cationic palladium complexes can polymerize norbornene alone without any cocatalysts and exhibit a high thermostability. Norbornene polymerization with the cationic palladium catalyst was proven to proceed through a coordination–insertion mechanism by NMR studies. Analysis of oligomers obtained by polymerizing the monomer in the presence of H2 reveals the existence of a C7 linkage in the polynorbornene (PNB) by σ-bond metathesis, which may be the reason for the insolublity of polynorbornenes obtained by palladium catalysts.

Imine‐N‐Heterocyclic Carbenes as Versatile Ligands in Ruthenium(II) p‐Cymene Anticancer Complexes: A Structure–Activity Relationship Study

“…The intermediate products N ‐(2,6‐diisopropylphenyl)acetamide, N ‐(2,6‐dimethylphenyl)acetamide, N ‐phenylbenzamide, N ‐(2,6‐dimethylphenyl)benzamide, N ‐(2,6‐dimethylphenyl)acetimidoyl chloride, N ‐(2,6‐diisopropylphenyl)acetimidoyl chloride, N ‐(2,6‐dimethylphenyl)benzenecarboximidoyl chloride, and N ‐phenylbenzenecarboximidoyl chloride were prepared according to previously reported procedures . The imine‐N‐heterocyclic carbene ligands L1–L4 , L5 ,– L6–L9 , and L10 – were prepared according to slightly modified procedures reported previously. For the biological experiments, Dulbecco′s Modified Eagle′s Medium (DMEM), fetal bovine serum, penicillin/streptomycin mixture, trypsin/EDTA, phosphate‐buffered saline (PBS), MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide), PI (propidium iodide), JC‐1 (5,5′,6,6′‐tetrachloro‐1,1′,3,3′‐tetraethylbenzimidazolyl carbocyanine iodide), and H 2 DCFDA (2′,7′‐dichlorodihydrofluorescein diacetate) were purchased from Sangon Biotech.…”

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The vinyl type polymers of norbornene are important for its dielectric property and are used in microelectronics applications [305] (Scheme 52). The complexes (341), [124] (360), [306] (548), [306] (557), [306] (570−573), [174] (574), [175] (622−623), [306] (677) [204] and (785) [175] catalyzed norbornene polymerization in the presence of MAO.…”

Pd(II) complexes bearing di‐ and monochelate fluorinated β‐ketonaphthyliminato ligand and their catalytic properties towards vinyl‐addition polymerization and copolymerization of norbornene and ester‐functionalized norbornene derivative

“…The reduced oxophilicity of late transition metal palladium(II) complexes endows the catalysts with the ability to produce copolymers with a variety of polar‐functionalized olefins, allowing the preparation of complex functional polymer architectures. Much significant work has been done by many researchers with palladium(II)‐based systems for the vinyl‐type addition polymerization of a wide variety of NB derivatives under mild conditions . Additionally, copolymerization of NB with 5‐NB‐2‐carboxylic acid methyl ester in toluene using the (Cp)Ni(Cl)(PPh 3 )/AlMe 3 /B(C 6 F 5 ) 3 system has been achieved in moderate yields (up to 68% in 2 h at room temperature) .…”