Unsymmetrical Fluorinated α‑Diimine Nickel Catalysts with Synergistic Steric and Fluorine Effects: toward Ethylene-Based Elastomers and Polar Copolymers

Abstract

Polyolefin elastomers and polar-functionalized polyethylene are crucial high-performance materials, yet their synthesis is constrained by trade-offs among molecular weight, polar comonomer incorporation, and catalyst stability. To address these challenges, we developed a series of unsymmetrical α-diimine Ni­(II) catalysts (Ni1–Ni5) that integrate steric shielding with a “fluorine effect.” Incorporation of a bulky dibenzhydryl substituent enhances thermal stability, while an ortho-fluorinated N-aryl unit electronically modulates the active site and suppresses chain transfer. These catalysts exhibit high activity and robustness in ethylene polymerization, affording polyethylene with high molecular weights (M _n up to 2.99 × 10⁵ g·mol^–1). Notably, the optimal catalyst further enables direct copolymerization of ethylene with long-chain ω-unsaturated alcohols and esters, yielding functionalized polyethylenes with appreciable polar comonomer incorporation. Furthermore, the resulting materials display excellent elastomeric properties, including excellent tensile strength (up to 34.6 MPa) and significantly enhanced elastic recovery (SR up to 68%), demonstrating the effectiveness of this catalyst design strategy.

1. Introduction

Polyolefins, especially polyethylene (PE), constitute the most widely produced class of synthetic polymers, with applications spanning packaging, agriculture, automotive, and medical industries. Their versatility stems from the ability to finely tune material propertiessuch as molecular weight, branching density, and functional comonomer incorporationlargely governed by the catalyst during polymerization. − While traditional Ziegler-Natta and early transition metal catalysts have long dominated industry, their limited tolerance for polar functional groups and microstructure control has stimulated substantial interest in late transition metal systems. − Notably, the α-diimine Ni­(II) and Pd­(II) catalysts pioneered by Brookhart and coworkers represent a milestone class, enabling branched polymers from ethylene alone through a unique chain-walking mechanism and exhibiting marked tolerance toward polar monomers. −

Nevertheless, significant challenges persist in optimizing these catalytic systems for practical and industrially relevant applications. − Principal limitations are (i) rapid chain transfer via β-H elimination, which restricts achievable polymer molecular weights, and (ii) insufficient thermal stability under industrially relevant temperatures. Conventional strategies to address these issues rely on steric modification of the ligand framework. In particular, bulky substituents, especially at the ortho-positions of the N-aryl rings, provide axial shielding to the metal center, hindering β-H elimination and chain transfer, thereby improving molecular weight and thermal stability. − However, excessive bulk can complicate synthesis, diminish catalytic activity, and still fail to fully suppress chain transfer at elevated temperatures.

In recent years, the “fluorine effect” has emerged as a powerful complementary design strategy. Owing to their minimal steric demand coupled with strong electron-withdrawing character, fluorine substituents enable subtle modulation of the electrophilicity of the metal center and the stability of key catalytic intermediates. ,− For example, Fujita demonstrated that fluorine can interact with the β-H of the growing polymer chain to suppress chain-transfer events, thereby enabling living ethylene polymerization with high activity and narrow molecular-weight dispersity (Figure A). , Ma and coworkers reported that, in Ni­(II) phenoxyimine systems, ortho-fluorine substitution enhances catalytic activity through a combination of steric effects and weak C–H···F interactions, while simultaneously regulating polymer branching and molecular weight via electronic modulation (Figure B). Within α-diimine nickel catalysts, Jian and coworkers achieved living ethylene polymerization at 130 °C by synergistically integrating steric shielding with fluorine effects, underscoring the pivotal role of fluorine in suppressing chain-transfer processes (Figure C).

1.

Representative fluorine-substituted transition-metal catalysts for ethylene polymerization.

Chen and coworkers further revealed that introducing a −CF₃ group markedly reduces branching while increasing melting point, glass-transition temperature, and molecular weight, attributed to interactions between the −CF₃ moiety and β-H of the propagating chain (Figure D). Thus, fluorinated catalysts frequently afford polyolefins with elevated molecular weights and enhanced thermal stability. Despite these advantages, fluorine modulation introduces additional challenges. Although fluorination often improves polymer regularity and molecular weight, it can impede the controlled synthesis of high-performance elastomers and polar-monomer copolymers. − Moreover, the fluorine effect is intrinsically temperature-sensitive, , influencing catalytic stability and controllability, and such systems remain prone to deactivation under industrially relevant high-temperature conditions.

To address these limitations, we herein integrate the established steric shielding strategy with fluorine-enabled electronic modulation and noncovalent interaction effects (Figure , this work). We hypothesize that an unsymmetrical α-diimine nickel catalyst bearing an ortho-fluorine substituent on one N-aryl ring and a bulky dibenzhydryl (CHPh₂) group on the opposite ring will deliver superior catalytic performance. The dibenzhydryl moiety provides effective steric protection of the active site, thereby enhancing thermal stability, whereas the ortho-fluorine substituent is expected to selectively suppress chain-transfer processes through electronic effects and potential weak noncovalent interactions. This cooperative design is intended to reconcile high catalytic activity with substantially improved polymer molecular weight and thermal robustness. In this context, we report the design, synthesis, and characterization of a novel series of unsymmetrical α-diimine nickel­(II) complexes (Ni1–Ni5) embodying this synergistic steric–fluorine principle. Their catalytic performance in ethylene homopolymerization is systematically evaluated across a temperature range, with emphasis on activity, thermal stability, and polymer properties including molecular weight, branching density, and mechanical performance. In addition, the applicability of these catalysts to the copolymerization of ethylene with long-chain polar monomers, such as ω-unsaturated alcohols and esters, was explored to access functionalized polyethylenes. Collectively, this work establishes a concerted steric–fluorine design strategy as a versatile and effective platform for advancing high-performance late transition metal olefin polymerization catalysts.

2. Results and Discussion

2.1. Synthesis and Characterization of the α-Diimine Ni­(II) Complexes

3-((2,6-Dibenzhydryl-4-methylphenyl)­imino)­butan-2-one (1) was synthesized according to a modified literature procedure (Figure ). Subsequently, compound 1 was condensed with a series of substituted anilines to afford the target unsymmetrical α-diimine ligands L1–L5 in good yields (63–79%). At room temperature, ligands L1–L5 were then reacted with (DME)­NiBr₂ (DME = 1,2-dimethoxyethane) in dichloromethane, providing the corresponding nickel complexes Ni1–Ni5 in excellent yields (91–96%). Ligands L1–L5 were fully characterized by ¹H NMR, ¹³C­{¹H} NMR, ¹⁹F­{¹H} NMR spectroscopy as well as high-resolution mass spectrometry (HR-MS) (for details, see Supporting Information). The synthesized nickel complexes Ni1–Ni5 were characterized by ESI-MS and elemental analysis. Furthermore, the molecular structures of complexes Ni1, Ni3–Ni5 were confirmed by single-crystal X-ray diffraction analysis.

2.

Synthesis of α-diimine nickel complexes.

The metal centers in complexes Ni1 and Ni3–Ni5 adopt distorted tetrahedral geometries, with bond lengths and angles that align well with those reported for conventional α-diimine catalyst systems (Figure a–d, Table S1–S2, Supporting Information). ,, All precatalysts exhibited similar structural characteristics, with the N-aryl planes oriented nearly perpendicular to the coordination plane around the nickel center. Notably, in complexes Ni1 (Ni1–F1:4.27 Å) and Ni4 (Ni1–F1:3.93 Å), the observed Ni–F distances substantially exceed the van der Waals contact distance of 3.50 Å, ruling out any direct Ni···F interactions. Nevertheless, the incorporation of fluorine into the ligand architecture may still modulate catalytic performance through multiple pathways. In addition to electronic modulation at the metal center, fluorine substituents can participate in noncovalent interactionssuch as with the β-H of the propagating polymer chain or with polar functional groups of comonomers. ,,,,, Such weak interactions are expected to suppress β-H elimination and alleviate catalyst deactivation by polar monomers, thereby favoring higher polymer molecular weights and enhanced comonomer incorporation. In addition, analysis of the buried volume (%V_bur) for complexes Ni1, Ni3, Ni4, and Ni5 reveals the trend: Ni4 > Ni1 > Ni3 > Ni5, with Ni4 exhibiting the largest steric encumbrance around the metal center (Figure e). These results suggest that fluorine incorporation contributes to an increase in the effective buried volume of the precatalyst, an effect that is further amplified when fluorine substitution is synergistically combined with appropriate steric elements, such as a methyl substituent.

3.

(a–d) Molecular structure of complexes Ni1 (CCDC Number 2334767) and Ni3–Ni5 (CCDC Number 2334769, 2334770, 2334771) with ellipsoids drawn at the 30% probability level (hydrogen atoms are omitted for clarity). (e) Topographic steric maps of α-diimine nickel complexes Ni1 and Ni3–Ni5.

2.2. Ethylene Polymerization

The ethylene polymerization performance of the synthesized Ni­(II) complexes (Ni1–Ni5) was systematically investigated under 8 atm ethylene pressure using AlEt₂Cl (Al/Ni = 300) as the cocatalyst, with temperature varied from 25 to 100 °C (Table ). All precatalysts exhibited high catalytic activities across the studied temperature range, reaching up to 2.62 × 10⁷·g_PE·mol_Ni ^–1·h^–1. Notably, the fluorine-containing precatalysts Ni1, Ni2 and Ni4 generally displayed higher activities than the non-fluorinated counterpart Ni3 and Ni5, particularly in the medium-temperature region (40–60 °C) (Figure a). For instance, at 60 °C, Ni2 achieved an activity of 2.62 × 10⁷·g_PE·mol_Ni ^–1·h^–1, nearly twice that observed for Ni3 (1.34 × 10⁷·g_PE·mol_Ni ^–1·h^–1) under identical conditions (Table , entry 8 vs. 13). These results indicate that ortho-fluorine substitution can effectively enhance catalytic efficiency, likely by suppressing chain-transfer reactions through weak F···H–C noncovalent interactions with the growing polymer chain. Furthermore, fluorine incorporation exerts a pronounced influence on polymer molecular weight (Figure b). Although an overall decrease in molecular weight with increasing temperature was observedconsistent with accelerated chain-transfer rates at elevated temperaturesthe fluorinated precatalyst Ni2 consistently yielded polymers with higher molecular weights than the non-fluorinated analogue Ni3 at equivalent temperatures (Table , entries 6–10 vs. 11–15). Moreover, the number of ortho-fluorine atoms on the N-aryl ring further modulates this effect. Specifically, Ni2, bearing two ortho-fluoro substituents, afforded polyethylene with noticeably higher molecular weights than its mono-fluorinated counterpart Ni1 under identical conditions (Table , entries 6–10 vs. 1–5). These findings indicate that the incorporation of ortho-fluorine atoms effectively suppresses β-H elimination along the growing polymer chain, thereby favoring the formation of high molecular weight polyethylene.

1. Ethylene Polymerization with Ni­(II) Complexes .

Entry	Cat.	T/°C	Yield/g	Act.	M n	Đ	B
1	Ni1	25	2.74	1.64	5.53	1.82	66
2	Ni1	40	3.39	2.03	2.41	2.15	67
3	Ni1	60	2.52	1.51	2.16	1.99	69
4	Ni1	80	2.25	1.35	1.71	1.94	76
5	Ni1	100	1.96	1.18	1.29	2.02	83
6	Ni2	25	2.71	1.63	9.23	1.73	71
7	Ni2	40	2.80	1.68	6.78	1.72	72
8	Ni2	60	4.36	2.62	3.86	2.00	75
9	Ni2	80	2.38	1.43	3.25	2.01	78
10	Ni2	100	0.82	0.49	2.20	1.84	85
11	Ni3	25	2.42	1.45	5.43	1.95	72
12	Ni3	40	2.27	1.36	2.69	2.11	73
13	Ni3	60	2.23	1.34	1.77	2.07	76
14	Ni3	80	1.76	1.06	1.62	2.00	77
15	Ni3	100	1.21	0.73	1.04	1.93	83
16	Ni4	25	2.12	1.27	29.98	1.93	80
17	Ni4	40	3.30	1.98	20.09	2.06	85
18	Ni4	60	2.98	1.79	14.83	1.97	89
19	Ni4	80	2.60	1.56	13.67	1.89	91
20	Ni4	100	2.30	1.38	11.07	2.08	90
21	Ni5	25	1.96	1.18	18.86	2.00	78
22	Ni5	40	2.14	1.28	15.27	2.14	78
23	Ni5	60	2.35	1.41	13.72	1.87	78
24	Ni5	80	2.18	1.31	10.88	2.01	81
25	Ni5	100	1.34	0.80	1.33	2.00	83

^aCondition: precatalyst (1 μmol), AlEt₂Cl (300 equiv), CH₂Cl₂ (2 mL), toluene (48 mL), 8 atm, 10 min.

^bThe activity (10⁷ g_PE·mol_Ni ^–1·h^–1) was determined from the mass of the polymer product.

^cMolecular weight (10⁴ g·mol^–1) and polydispersity index (Đ) were determined by gel permeation chromatography (GPC).

^dBranches per 1000 carbon atoms, determined by ¹H NMR analysis.

4.

Comparison of (a) catalytic activities, (b) molecular weights of the polyethylene obtained by Ni1–Ni5 at 25–100 °C.

The introduction of additional steric bulkexemplified by Ni4, which features both a methyl and a fluorine groupsresulted in a significant increase in polymer molecular weight, reaching up to 2.99 × 10⁵ g·mol^–1 at 25 °C. This enhancement, however, was accompanied by a moderate decrease in catalytic activity relative to the less sterically encumbered Ni1 (Table , entry 16 vs. 1). These observations indicate that steric shielding alone can effectively suppress chain transfer and elevate molecular weight, although it may slightly slow monomer insertion. ,, In contrast, the non-fluorinated analogue Ni5 exhibited both lower catalytic activities and reduced polymer molecular weights than Ni4 under identical conditions, highlighting the distinct contribution of fluorine substitution (Table , entries 16–20 vs. 21–25). Together, these results demonstrate that ortho-fluorine incorporation in unsymmetrical α-diimine nickel catalysts not only enhances catalytic activity but also promotes higher polymer molecular weights by mitigating chain-transfer processes. ,, The synergistic integration of fluorine-mediated electronic and noncovalent effects with rationally tuned steric shielding therefore represents a promising strategy for the design of high-performance catalysts that achieve an optimal balance of activity, thermal stability, and polymer properties.

Building upon the initial screening, we further evaluated the performance of the optimal fluorinated catalyst Ni2 under extended polymerization durations and varied ethylene pressures to assess its operational stability and pressure-dependent behavior (Table ). When the polymerization time was extended from 10 to 120 min at 60 °C and 8 atm ethylene, the total polymer yield increased progressively from 4.36 to 8.52 g (Table , entry 8 vs. Table , entries 1–3). Notably, the catalyst maintained appreciable activity over the extended period, and the molecular weight of the produced polyethylene rose from 3.86 × 10⁴ to 5.02 × 10⁴ g·mol^–1, with the branching density remaining stable around 72–73 branches per 1000 carbons. This indicates robust stability of the Ni2 system with suppressed deactivation under prolonged operation, a critical attribute for potential scale-up.

2. Effect of Conditions on Ethylene Polymerization with Ni2 .

Entry	P/atm	Time/min	Yield/g	Act.	M n	Đ	B
1	8	30	4.88	0.98	4.05	2.82	73
2	8	60	6.03	0.60	4.32	2.64	72
3	8	120	8.52	0.43	5.02	2.41	72
4	2	10	0.97	0.58	2.12	2.41	79
5	4	10	1.74	1.04	2.88	2.22	75
6	20	10	4.41	2.65	4.60	2.56	74
7	30	10	4.56	2.74	4.91	2.62	74

^aCondition: precatalyst Ni2 (1 μmol), AlEt₂Cl (300 equiv), CH₂Cl₂ (2 mL), toluene (48 mL), 60 °C.

^bThe activity (10⁷ g_PE·mol_Ni ^–1·h^–1) was determined from the mass of the polymer product.

^cMolecular weight (10⁴ g·mol^–1) and polydispersity index (Đ) were determined by gel permeation chromatography (GPC).

^dBranches per 1000 carbon atoms, determined by ¹H NMR analysis.

Furthermore, the influence of ethylene pressure on the polymerization was systematically investigated at 60 °C. As the pressure increased from 2 to 30 atm (Table , entries 4–7), both catalytic activity and polymer molecular weight exhibited a positive correlation, rising from 0.58 × 10⁷·to 2.74 × 10⁷·g_PE·mol_Ni ^–1·h^–1 and from 2.12 × 10⁴ to 4.91 × 10⁴ g·mol^–1, respectively. The branching density showed a slight decrease from 79 to 74 branches per 1000 carbons with increasing pressure, consistent with the expected reduced chain-walking probability under higher ethylene concentration. These results confirm that Ni2 performs efficiently across a broad pressure range, maintaining high activity and molecular weight controlkey features for tailoring polymer properties under different process conditions.

2.3. Ethylene/Polar Monomer Copolymerization

The direct copolymerization of ethylene with polar monomer to access functionalized polyolefins remains a significant synthetic challenge, and studies employing fluorinated α-diimine nickel complexes in this context are comparatively limited. ,,, Based on their high performance in ethylene homopolymerization, catalysts Ni1, Ni2, and Ni4 were selected to evaluate their ability to incorporate long-chain polar monomers, such as hex-5-en-1-ol (HO), dec-9-en-1-ol (DO), undec-10-en-1-ol (UO), and methyl 10-undecenoate (MU) (Table ). All three catalysts successfully mediated the copolymerization, yielding polymers with moderate polar-monomer incorporation (0.38–1.80 mol %) and appreciable activities (up to 5.03 × 10⁵ g_PE·mol_Ni ^–1·h^–1).

3. Ethylene/Polar Monomer Copolymerization .

Entry	Cat.	Monomer	Yield/g	Act.	X M/%	Mn	Đ	B
1	Ni1	HO	7.90	3.95	0.56	2.07	2.55	81
2	Ni1	DO	10.06	5.03	0.49	0.60	3.28	80
3	Ni1	UO	2.18	1.09	1.80	0.61	3.30	77
4	Ni1	MU	0.87	0.44	0.72	0.38	2.22	92
5	Ni2	HO	5.53	2.77	0.40	2.92	1.76	87
6	Ni2	DO	1.89	0.95	0.38	2.28	2.12	88
7	Ni2	UO	2.75	1.38	1.70	4.27	2.26	81
8	Ni2	MU	5.26	2.63	0.57	0.78	2.67	86
9	Ni4	HO	2.22	1.11	0.61	13.55	1.85	98
10	Ni4	DO	3.06	1.53	0.92	12.98	1.70	91
11	Ni4	UO	1.91	0.96	0.73	15.31	2.42	98
12	Ni4	MU	2.56	1.28	0.47	1.95	2.61	78

^aCondition: precatalyst (20 μmol), [M]_Monomer: 0.25 mol/L AlEt₂Cl (300 equiv), CH₂Cl₂ (2 mL), total solution volume (20 mL), 2 atm, 25 °C, 1 h.

^bThe activity (10⁵ g_PE·mol_Ni ^–1·h^–1) was determined from the mass of the polymer product.

^cX_M = Comonomer incorporation (mol %), determined by ¹H NMR analysis.

^dMolecular weight (10⁴ g·mol^–1) and polydispersity index (Đ) were determined by gel permeation chromatography (GPC).

Furthermore, a comparison between the mono-fluoro (Ni1) and difluoro (Ni2) catalysts reveals that increasing the number of fluorine substituents decreases polar-monomer incorporation while concurrently increasing copolymer molecular weight (Table , entries 1–4 vs. 5–8). This contrasting behavior reflects the multifaceted role of fluorine. , The strong electron-withdrawing character of fluorine, coupled with potential noncovalent F···H–C interactions, suppresses β-H elimination and chain-transfer events, thereby prolonging chain growth and increasing molecular weighta trend further enhanced for the difluoro-substituted Ni2. Conversely, difluoro substitution increases both the electrophilicity of the metal center and steric congestion around the active site, likely impeding coordination and insertion of polar monomers and thus reducing incorporation. Notably, under identical reaction conditions, complex Ni4 consistently afforded copolymers with higher molecular weights (M _n up to 15.3 × 10⁴ g·mol^–1) than Ni1 and Ni2. Moreover, Ni4 also delivered superior polar-monomer incorporation in most cases (Table , entries 9–12 vs. 1–8). These results underscore that the synergistic combination of increased steric bulk at the ortho-positions of the N-aryl ring and the fluorine effect not only promotes higher copolymer molecular weights but also effectively facilitates polar-monomer incorporation, achieving a balanced enhancement in both key performance metrics.

2.4. Mechanical Properties of Polyethylene

Polyethylenes produced using catalysts Ni4 and Ni5 over a range of polymerization temperatures exhibit high molecular weights and moderate branching densities, imparting characteristic elastomeric behavior. The mechanical performance of these polymers could be effectively tuned over a broad spectrum (Figure and Figure S1, Supporting Information). All samples displayed high ductility with strain-at-break values ranging from 1500 to 4249%, together with moderate to high tensile strength, as reflected by stress-at-break values of 4.1–34.6 MPa, exceeding those reported for most analogous systems. − ,, A general decline in stress-at-break with increasing polymerization temperature is observed for both catalyst systems (Figure a and Figure S1).

5.

(a) Stress-strain curves and (b–i) plots of hysteresis experiments of ten cycles at a strain of 300% for polyethylene.

Under identical conditions, polyethylenes derived from the non-fluorinated catalyst Ni5 consistently exhibited higher ultimate tensile strength and toughness compared to those from its fluorinated analog Ni4. This enhancement can be attributed to the lower branching density and more linear chain architecture of the Ni5-produced polyethylene, which facilitate improved chain alignment and stronger intermolecular interactions, thereby enhancing mechanical strength. However, at elevated polymerization temperatures (>60 °C), polyethylenes synthesized with Ni5 no longer display elastomeric characteristics. In contrast, the fluorine-containing catalyst Ni4 maintains elastomeric behavior over a wider temperature range, underscoring the role of fluorine in expanding the accessible processing window for mechanical property modulation.

To evaluate elastic recovery, cyclic tensile tests were conducted by repeatedly loading and unloading the samples to 300% strain for ten cycles (Figure b–i). All materials underwent an initial irreversible structural rearrangement during the first cycle, followed by stable and reproducible elastomeric responses in subsequent cycles. Notably, polyethylenes prepared with the fluorinated catalyst Ni4 exhibit superior elastic recovery, with strain recovery (SR) values of 58–68%, compared with 39–61% for Ni5. This enhanced elastic recovery is consistent with the ability of fluorine substitution to suppress β-H elimination leading to higher molecular weights capable of efficient strain recovery. Collectively, these results underscore the critical role of fluorine substitution in governing the mechanical performance of polyethylene. By increasing molecular weight and modulating chain architecture, the fluorine effect significantly enhances both tensile strength and elastic recovery, offering a versatile and distinctive strategy to finely tailor polyolefin properties. This synergistic steric-fluorine design demonstrates clear advantages over existing systems in its ability to finely regulate polymer microstructure, thereby enabling superior elastomeric performance (Table S3, Supporting Information). −

To elucidate the microstructure of the branched polyethylene and its correlation with the observed mechanical performance, ¹³C­{¹H} NMR analysis was performed on a representative sample synthesized with Ni4 at 25 °C (Table , entry 16). The spectrum reveals a branching distribution comprising methyl (71.8%), ethyl (4.7%), propyl (4.7%), and long-chain branches (18.8%) (Figure ). The predominance of methyl branches is consistent with the chain-walking mechanism characteristic of α-diimine nickel catalysts, while the appreciable content of long-chain branches (LCBs) is particularly noteworthy. These LCBs contribute to the formation of an entangled network that enhances elastic recovery, as evidenced by the high strain recovery (SR = 58%) of this sample. However, the same network structure also reduces the ability of chains to align and crystallize under tension, which accounts for the moderate sacrifice in ultimate tensile strength compared to more linear analogues. As the polymerization temperature increases, both the overall branching density and the proportion of long-chain branches rise, a trend attributable to thermally accelerated chain walking. This microstructural evolution directly underpins the temperature-dependent mechanical behavior: higher branching and entanglement improve elasticity but concurrently limit the achievable strength, thereby illustrating how catalyst design and polymerization conditions can be leveraged to tailor polyolefin architecture and hence material properties.

6.

¹³C NMR spectrum of polyethylene (Table , entry 16).

3. Conclusions

In summary, we have developed a new series of unsymmetrical α-diimine Ni­(II) catalysts (Ni1–Ni5) by synergistically integrating bulky dibenzhydryl steric shielding with ortho-fluorine electronic modulation. This cooperative design effectively addresses key challenges associated with chain-transfer reactions and thermal instability. The fluorinated catalysts (Ni1, Ni2, Ni4) demonstrated superior ethylene homopolymerization performance, delivering high activities (up to 2.74 × 10⁷ g_PE·mol_Ni ^–1·h^–1) and producing polyethylene with markedly elevated molecular weights (M _n up to 2.99 × 10⁵ g·mol^–1), attributable to fluorine-enabled suppression of β-H elimination. Notably, precatalyst Ni4 maintains excellent thermal stability up to 100 °C and effectively mediates the copolymerization of ethylene with long-chain polar comonomers, affording functionalized polyethylenes with appreciable incorporation. Moreover, polymers from fluorinated catalysts displayed enhanced elastomeric properties, including high ductility and improved elastic recovery. Collectively, this work establishes a synergistic steric-fluorine strategy as a versatile and effective platform for the development of advanced late transition metal catalysts toward high-performance, functional polyolefins with tailored properties.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/polymscitech.5c00139.

• Additional experimental details, materials, and methods; procedures for ethylene polymerization and copolymerization with polar monomers; synthesis and characterization of ligands L1–L5 and nickel complexes Ni1–Ni5; NMR spectra of all new compounds and polymers; GPC traces of polymers; ESI-MS spectra of catalysts; X-ray crystallographic data for complexes Ni1 and Ni3–Ni5; mechanical property data (stress–strain curve) for polyethylene samples; comparison of catalytic performance with previously reported nickel catalysts (PDF)

• Crystallographic information file for Ni1 (CIF)

• Crystallographic information file for Ni3 (CIF)

• Crystallographic information file for Ni4 (CIF)

• Crystallographic information file for Ni5 (CIF)

J.-K.L.: Writingoriginal draft, Investigation, Formal analysis, Data curation. Y.F.: Formal analysis. J.N.: Data curation. H.W.: Data curation. M.-P.S.: Funding acquisition. J.-F.G.: Data curation, Supervision. H.J.: Writingreview and editing, Methodology supervision, Project administration, Funding acquisition, Conceptualization.

The authors declare no competing financial interest.