Ethylene polymerization using heterogeneous multinuclear nickel catalysts supported by a crosslinked alpha diimine ligand network

A crosslinked alpha diimine ligand supporting a nickel metal center polymerizes ethylene to produce polyethylene with controlled microstructures, high activities, and can be removed from the product.

Synthesis and structures of mono- and di-nuclear aluminium and zinc complexes bearing α-diimine and related ligands, and their use in the ring opening polymerization of cyclic esters

Multi-metallic complexes (of Al, Zn) derived from imine-based ligands effectively operate as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and co-polymerization thereof.

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

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.

Synthesis of low to high molecular weight poly(1-hexene); rigid/flexible structures in a di- and mononuclear Ni-based catalyst series

Poly(1-hexene)s with a wide range of M_w and MWD using mono- and dinuclear rigid/flexible bridged Ni catalysts; structure–property relation.

"Living" Polymerization of Ethylene and 1-Hexene Using Novel Binuclear Pd⁻Diimine Catalysts

We report the synthesis of two novel binuclear Pd–diimine catalysts and their unique behaviors in initiating “living” polymerization of ethylene and 1-hexene. These two binuclear catalysts, [(N^N)Pd(CH₂)₃C(O)O(CH₂)_mO(O)C(CH₂)₃Pd(N^N)](SbF₆)₂ (3a: m = 4, 3b: m = 6) (N^N≡ArN=C(Me)–(Me)C=NAr, Ar≡2,6–(iPr)₂C₆H₃), were synthesized by simply reacting [(N^N)Pd(CH₃)(N≡CMe)]SbF₆ (1) with diacrylates, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate, respectively. Their unique binuclear structure with two identical Pd–diimine acrylate chelates covalently linked together through an ester linkage was confirmed by NMR and single crystal XRD measurements. Ethylene “living” polymerizations were carried out at 5 °C and under ethylene pressure of 400 and 100 psi, respectively, with the binuclear catalysts, along with a mononuclear chelate catalyst, [(N^N)Pd(CH₂)₃C(O)OMe]SbF₆ (2), for comparison. All the polyethylenes produced with both binuclear catalysts show bimodal molecular weight distribution with the number-average molecular weight of the higher molecular weight portion being approximately twice that of the lower molecular weight portion. The results demonstrate the presence of monofunctional chain growing species resembling catalyst 2, in addition to the expected bifunctional species leading to bifunctional “living” polymerization, in the polymerization systems. Both types of chain growing species exhibit “living” characteristics under the studied conditions, leading to the simultaneous linear increase of molecular weight in both portions. However, when applied for the “living” polymerization of 1-hexene, the binuclear catalyst 3a leads to polymers with only monomodal molecular weight distribution, indicating the sole presence of monofunctional chain growing species. These two binuclear catalysts are the first Pd–diimine catalysts capable of initiating bifunctional ethylene “living” polymerization.

Influence of Ligand Backbone Structure and Connectivity on the Properties of Phosphine-Sulfonate Pd(II)/Ni(II) Catalysts

Phosphine-sulfonate based palladium and nickel catalysts have been extensively studied in ethylene polymerization and copolymerization reactions. Previously, the majority of the research works focused on the modifications of the substituents on the phosphorous atom. In this contribution, we systematically demonstrated that the change of the ligand backbone from benzene to naphthalene could greatly improve the properties of this class of catalysts. In the palladium system, this change could increase catalyst stability and polyethylene molecular weights. In the nickel system, this change could dramatically increase the polyethylene molecular weights. Most interestingly, the change in the connectivity of phosphine and sulfonate moieties to the naphthalene backbone could also significantly influence the catalyst properties.

Direct Synthesis of Branched Carboxylic Acid Functionalized Poly(1-octene) by α-Diimine Palladium Catalysts

In this work, we studied propylene polymerization using some α-diimine palladium catalysts with systematically varied ligand sterics. In propylene polymerization, the ligand steric effect exhibits significant variations on the catalytic activity, polymer molecular weight, and branching density. However, the regio control for the polymer microstructure is poor. Furthermore, copolymerization of 1-octene with the highly challenging and biorenewable comonomer acrylic acid was investigated. High copolymer molecular weights and high comonomer incorporation ratios could be achieved in this system. This study provides a novel access for the direct synthesis of branched carboxylic acid functionalized polyolefins.

Redox control in palladium catalyzed norbornene and alkyne polymerization

Switchable polymerization of norbornene, 5-norbornene-2-yl acetate and 1-chloro-1-octyne could be realized by using two palladium complexes (NHC)Pd(allyl)Cl (NHC = 1,3-Ar₂-naphthoquinimidazolylidene, Ar = 2,6-Me₂-C₆H₃, 2,6-ⁱPr₂-C₆H₃) bearing a redox-active naphthoquinone moiety.

Ligand steric effects on α-diimine nickel catalyzed ethylene and 1-hexene polymerization

α-Diimine nickel complexes with systematically varied ligand sterics were used as a precatalyst for ethylene and 1-hexene polymerizations. The catalytic activities, molecular weights and branching densities could be tuned over a very wide range.

Modulating Polyolefin Copolymer Composition via Redox-Active Olefin Polymerization Catalysts

The ability to precisely modulate polymer architecture and composition is a long-standing goal within the field of polymer synthesis. Herein, we demonstrate that redox-active olefin polymerization catalysts may be used to predictably tailor polyolefin comonomer incorporation levels for the copolymerization of ethylene and higher α-olefins. This ability is facilitated via the utilization of a redox-active olefin polymerization catalyst that once reduced via in situ addition of a chemical reductant results in a notable drop in α-olefin incorporation. We attribute this behavior to the reduced catalyst's increased electron density and its concomitant decreased rate of α-olefin consumption. These results are supported by investigations into propylene and 1-hexene homopolymerizations as well as detailed GPC, DSC, GC, and NMR analyses.

Novel zirconium complexes with constrained cyclic β-enaminoketonato ligands: improved catalytic capability toward ethylene polymerization

Novel Zr(iv) and Hf(iv) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArN[double bond, length as m-dash]CH-C8H3(CH2)n(R)O]2MBn2, M = Zr or Hf; n = 1, 2 or 3; R = H or C6H5; Ar = C6H5 or C6F5} were synthesized and clearly characterized. X-ray crystal structure analysis reveals that these complexes adopt a distorted octahedral geometry. Compared with non-constrained analogues, the Zr(iv) complexes with a cyclic skeleton exhibited high catalytic activities (up to 16.4 kgPE mmolZr(-1) h(-1)) toward ethylene polymerization at ambient pressure and elevated temperatures. Moreover, the catalytic properties of these complexes could be governed exquisitely by appropriate variation of the N-aryl substituents and the size of the benzocyclane. The Zr(iv) complexes bearing a non-fluorinated N-aryl group yielded oligomers, while the fluorinated analogues bearing a five-membered or six-membered cyclane group produced high molecular weight polyethylenes (33.4-306 kg mol(-1)) under similar conditions on account of the suppression effects on β-H elimination. The Zr(iv) complexes are more active toward ethylene polymerization than the Hf(iv) analogues, and the resulting polymers exhibited higher molecular weight and narrower molecular weight distribution.

Ethylene polymerization by salicylaldimine nickel(ii) complexes containing a dibenzhydryl moiety

The synthesis, characterization and ethylene polymerization properties of a series of salicylaldimine Ni(ii) complexes with a dibenzhydryl moiety are described.

Influence of ligand second coordination sphere effects on the olefin (co)polymerization properties of α-diimine Pd(ii) catalysts

A series of α-diimine ligands and their corresponding palladium complexes were synthesized and characterized.

Dinuclear nickel(ii) complexes with 2,5-diamino-1,4-benzoquinonediimine ligands as precatalysts for the polymerization of styrene: electronic and steric substituent effects

Substituent effects of the electron-donating ability and bulkiness of R in [{Ni(acac)}₂(μ-RAp)] (RApH₂: azophenines) on properties and catalytic activity are reported.

Synthesis, characterization and ethylene polymerization behaviour of binuclear nickel halides bearing 4,5,9,10-tetra(arylimino)pyrenylidenes

Binuclear nickel halides were found to be long-lived, high active ethylene polymerization catalysts; the polyethylene possessed branched features.