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

Abstract

Here we will summarize some of the recent advances in α-diimine ligand developments, as well as some new and challenging monomers that this class of catalysts can address through these ligand improvements.

Bulky iminophosphine‐based nickel and palladium catalysts bearing 2,6‐dibenzhydryl groups for ethylene oligo‐/polymerization

“…Complex Ni2 bearing strong electron‐withdrawing fluorine substituent of para ‐position in anilinic moiety demonstrated higher activity and higher molecular weights than the corresponding Ni2 (Table , entries 1–3 vs 4−6), probably because of the increased electrophilicity. This differences seen are consistent with previous literature on Brookhart‐type catalyst studies . We suggest that an interaction between the fluorine atoms and Al (III) activators blocks the apical positions of the catalytically active nickel center, which may reduce effectively associative olefin exchange reactions .…”

“…The branching structures analysis based on 13 C NMR showed that only 28 methyl branches were observed for Ni2 at 25 °C (Figure , Table , entry 4). The lower degree of branching density for the sterically bulkier catalysts are probably due to the relatively greater preference of insertion of ethylene into a primary metal alkyl species versus insertion into a secondary metal alkyl species …”

“…Many researches demonstrated recently that the ortho ‐dibenzhydryl moiety installed in the ligand can greatly enhance the catalytic performance of Ni and Pd complexes in terms of polymer molecular weights, catalytic activities as well as thermal stabilities . For example, Long and Chen et al .…”

Polar‐Functionalized, Crosslinkable, Self‐Healing, and Photoresponsive Polyolefins

“…Transition‐metal‐catalyzed olefin copolymerization with polar comonomers represents an efficient and attractive route for introducing functional groups that can improve polyolefin properties . Recently, several palladium‐ and nickel‐based catalysts have been reported with these capabilities . For example, phosphine sulfonate and related palladium catalysts have been extensively studied and can copolymerize ethylene with various polar comonomers …”

Facile synthesis of sterically demanding SHOP‐type nickel catalysts for ethylene polymerization

“…Nickel and palladium based complexes supported by different types of ligands have been extensively utilized as olefin oligo/polymerization catalysts for decades both in academia and industry because of their low oxophilicity and copolymerizing capability of the olefin with polar comonomers . The chain‐walking process has received extensive researches in ethylene oligo−/polymerization using these catalysts to produce polyethylene (PE) possessing unique branched structures .…”