Enhancing Thermal Stability and Living Fashion in α-Diimine–Nickel-Catalyzed (Co)polymerization of Ethylene and Polar Monomer by Increasing the Steric Bulk of Ligand Backbone

Abstract

Development of thermally stable nickel-based catalysts is highly desirable for industrial gas-phase olefin polymerizations. On the basis of the strategy of promoting the thermostability of nickel catalyst by the ligand backbone, we herein reported novel dibenzobarrelene-derived α-diimine nickel precatalysts for ethylene polymerization. Increasing the steric bulk on the ligand backbone was expected to inhibit the N-aryl rotation of the α-diimine ligands by the repulsive interactions, thus enhancing thermal stability (100 °C) and living fashion a temperatures up to 80 °C. Bulk ligand backbone also improved tolerance of nickel catalyst toward polar groups, and the α-diimine nickel catalyst containing a 2,6-t Bu-dibenzobarrelene backbone catalyzed living copolymerization of ethylene and methyl 10-undecenoate.

Recent advances in thermally robust, late transition metal‐catalyzed olefin polymerization

“…Wu and co‐workers extended these efforts to restrict N ‐aryl rotations via α ‐diimine modifications to include catalysts 21 and 22 , which feature a ‘wedge‐shaped’ dibenzobarrelene‐derived α ‐diimine ligand (Fig. ) . As a note, a related Ni α ‐diimine catalyst containing an unsubstituted dibenzobarrelene backbone was previously reported by Coates and co‐workers, and was shown to polymerize ethylene in a living manner at room temperature .…”

“…More specifically, they demonstrated that the 2,6‐dimethylphenyl‐substituted catalyst 21 can polymerize ethylene in a living fashion at temperatures as high as 65 °C, whereas polymerization using the bulkier 2,6‐diisopropylphenyl‐substituted catalyst 22 proved to be living at temperatures as high as 80 °C. Further increasing polymerization temperatures to 100 °C revealed that while catalyst 22 remains active, it did deactivate slowly over the course of the 60 min polymerization …”

Emerging Palladium and Nickel Catalysts for Copolymerization of Olefins with Polar Monomers

“…[41] Considering the impressive reactivity of the Brookhart catalysts toward norbornene, [42] and their excellent tolerance toward ester functionalities,C hen and co-workers successfully copolymerized ethylene with polar functionalized norbornenes using a-diimine palladium catalysts. [43,44] Coates and co-workers [45] and Gao and co-workers [46] demonstrated that a-diimine nickel catalysts can mediate ethylene copolymerization with methyl 10-undecenoate.…”

Highly resilient polyethylene elastomers prepared using α‐diimine nickel catalyst with highly conjugated backbone

“…However, such bulky substituents were found to reduce the branching density of polyethylenes compared with B-Cat. [18,[44][45][46] Chen et al synthesized a series of α-diimine Ni(II) complexes with various substituents on the backbone, and the α-diimine Ni(II) complexes with two methoxy substituents on the ortho position of the acenaphthyl backbone could produce polyethylene with three times higher molecular weight than that using B-Cat (Figure 1, IX). [25] Modification of the backbone part of an α-diimine ligand is another potential strategy for improving the catalyst's molecular-weight ability.…”