Substituent effects and activation mechanism of norbornene polymerization catalyzed by three-dimensional geometry α-diimine palladium complexes

Abstract

A series of three-dimensional geometry 9,10-dihydro-9,10-ethanoanthracene-11,12-diimine methyl palladium chloride complexes were synthesized and characterized. These three-dimensional geometry a-diimine palladium complexes exhibited high activities toward the homopolymerization of norbornene and copolymerization of norbornene with 5-norbornene-2-carboxylic acid methyl ester in the presence of B(C 6 F 5 ) 3 . It was observed that the palladium-halogen bond of the complexes could be effectively activated by B(C 6 F 5 ) 3 . The activation mechanism was clarified by the end group analysis of the polymer, which provided a new pathway for the activation of palladium complexes. Meanwhile, the palladium catalysts with a three-dimensional geometry on the backbone were found to show a good thermal stability and afford a high incorporation of the polar monomer in norbornene polymerization. Moreover, the a-diimine palladium complexes with a large steric hindrance or strongly electron-donating group on the aryl ring of ligands could achieve a higher reactivity.

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

“…Three-dimensional geometry Ni-and Pd-based α-diimine complexes with a bulky bridged backbone. [105][106][107][108][109][110][111] played high thermal stability, high activities of up to 3.2 × 10 6 g PE (mol Pd h) −1 (60°C, 15 min), and high polymer M n (up to 538 000) in ethylene polymerization. More interestingly, semicrystalline low-density branched (23-29/1000 C) PEs with high T m of up to 99°C were obtained.…”

“…17) bearing a dibenzobarrelene backbone. [105][106][107][108] The precision synthesis of functionalized polyolefins was achieved by Pdcatalyzed living coordination copolymerization of ethylene with various acrylate comonomers. 105 In this system, the molecular weight, polydispersity, composition and branching topology of the E/MA copolymers can be tuned by changing ethylene pressure.…”

Switchable Polymerization of Norbornene Derivatives by a Ferrocene‐Palladium(II) Heteroscorpionate Complex

“…Vinyl polynorbornenes are important materials for optical applications due to their excellent thermal stability, high glass transition temperatures, small birefringence, and dielectric loss However, polynorbornenes are brittle, even at high molecular weights, display poor adhesion to common substrates, poor solubility in common organic solvents, and cannot be melt processed due to decomposition . Modifying the norbornene monomers with functional groups increases the solubility of the resulting polymers and improves their processability .…”

“…Amongst transition metal catalysts, palladium‐based systems are highly active toward norbornene polymerization and produce high molecular weight vinyl polynorbornenes , . Most palladium catalysts feature bidentate or monodentate supporting ligands since an open coordination sphere is necessary for monomer coordination , , , . Commonly employed systems also require the use of strong Lewis acids/alkylating reagents (i.e.…”

Investigations into the reactivity of lithium indenyl with alpha diimines with chlorinated backbones and formation of related functional ligands and metal complexes

“…Tuning the electronic and structural properties of the ligand by changing its donor functionalities (in type and / or number), bite angle, bulkiness and chirality, has marked effects on transition metal catalysis [2,3,27,28]. We describe here the synthesis and characterisation of a new class of ligands.…”