Neutral Nickel Catalysts Research Articles

Polymerization of Ester-Functionalized Norbornenes Using Neutral Nickel Catalysts

Polymerization of Ester-Functionalized Norbornenes Using Neutral Nickel Catalysts

Mono- and bi-nuclear phosphine-phenolate neutral nickel catalysts via simple Schiff-Base condensation for ethylene polymerization

In catalytic olefin polymerization, a significant amount of effort has been invested to modify either phosphine substituent or ligand backbone in recently advanced phosphine-phenolate [P,O] neutral nickel catalysts. Unlike other commonly used ligands like phenoxy-imines [N,O] and α-diimines [N,N], [P,O] ligands often require a laborious synthesis technique, which has hindered the rational design of ligand structures and the development of new catalysts. Here we present a novel and effective strategy for creating catalysts using [N,O,P] hybrid ligands. The substituent adjacent to the phenoxy group can be efficiently modified through straightforward Schiff-base condensation reactions with various amines that have established synthetic routes and diverse structures. This process results in the preparation of a series of highly active [P,O] nickel catalysts (up to 1.7 × 107 g mol-1h−1) that are capable of producing ultrahigh molecular weight polyethylene (UHMWPE) (Mw = 243.7 × 104 g/mol) in ethylene polymerization. The additional binding site greatly facilitates modulation of catalytic properties by additives, and parameters such as catalytic activity, polymer molecular weight, and polymer branching can be tuned in this way. Furthermore, binuclear [P,O] neutral nickel catalysts for olefin polymerization are synthesized for the first time using a sequence of diamines. The strategy presented in this work greatly improves the efficiency for the design and synthesis of [P,O] nickel and related catalysts. These findings will be advantageous for future catalyst design and screening.

Copolymerization of ethylene with polar styrene monomers catalyzed by phosphino‐dihydronaphtholate neutral nickel catalysts

AbstractThe physical properties of traditional polyolefin materials can be significantly improved by introducing polar groups, especially polar aromatic groups. However, it remains a major challenge to realize the highly effective copolymerization of ethylene with styrene derivatives. In this study, the direct copolymerization of ethylene with various polar styrene monomers bearing functional groups (o‐OMe, m‐OMe, p‐OMe, o‐Cl, m‐Cl, p‐ClSt, o‐F, o‐Br, p‐Me, p‐Ph, p‐Vinyl, p‐COOH, and C6F5) was achieved using phosphino‐dihydronaphtholate neutral nickel catalysts Ni1‐Ni3. Additionally, the catalytic behavior and the applicability of the polar monomer were evaluated in detail by copolymerization results. Catalysts Ni1‐Ni3 demonstrated inactivity towards the polymerization of polar styrene monomers but exhibited moderate catalytic activities in the copolymerization of ethylene with polar styrene monomers, yielding moderate‐molecular‐weight (Mw > 10 kDa) copolymers with the polar monomer contents ranging from 1.32 to 4.16 mol%. The steric and electronic effects of the substituent depending on the types and position in the phenyl ring considerably influenced the copolymerization behavior. Furthermore, comprehensive NMR analyses of the produced copolymers revealed that the polar monomers formed in‐chain insertions, saturated chain ends, and unsaturated chain ends after incorporation.

Synthesis of UHMWPE by neutral phosphine-phenolate based nickel catalysts

It is highly interesting to prepare polyethylene with ultra-high molecular weight under homogeneous conditions by nickel based neutral P^O type catalysts. In this contribution, ligand remote electronic effect was explored in some sterically hindered phosphine-phenolate based neutral nickel catalysts Ni1–Ni3 to afford UHMWPE. The maximal activity of these catalysts was found to be 1.33 × 106 g mol−1 h−1, which is quite active. The nickel catalysts retained considerable activity at high temperature of 120 °C showing their good thermal stability. More importantly, all these catalysts are capable of generating UHMWPE with maximum Mn of 2.51 × 106 g mol−1 by Ni2. The minimum distance between the Ni center and the oxygen of the 2,6-dimethoxy-1,1′-biphenyl unit attached with the phosphorous atom in Ni1 was recorded as 3.154 Å, which exactly matches with the van der Waals radii of oxygen and nickel. This provides an effective shield around the metal by preventing chain transfer and resulting to enhance the molecular weight of polymer. Combined with steric the remote substituents effect also crucial both to modulate activity and molecular weight of polymers.

Impact of Labile Ligands on Catalyst Initiation and Chain Propagation in Ni-Catalyzed Ethylene/Acrylate Copolymerization

Polar polyolefin synthesis by coordination polymerization is of high interest, but the catalysts’ low activity limits industrial implementation. Herein, we demonstrate how the nature of the labile ligand, L, impacts the performance of neutral nickel catalysts supported by bidentate phosphine-phenoxide and phosphine-enolate ligands in ethylene/acrylate copolymerization. By tuning L, the copolymerization activity reaches ∼24000 kg/(mol h). In situ studies indicate that a weaker L leads to faster chain propagation and more efficient catalyst initiation. Overall, this work highlights the potential of a strategy to improve catalyst activity in polar polyolefin synthesis complementary to design optimization for the bidentate ligand.

A readily available neutral nickel catalyst for accessing linear ultrahigh molecular weight polyethylene in a living manner

It is of great importance and is highly desired in the olefin polymerization catalysis that a simple catalyst derived from cheap starting materials and short synthetic pathways exhibits superior catalytic property towards a polymerization reaction. In this contribution, starting from commercially available and cheap materials, by using a short and simple three-step reaction route we report a readily available neutral phenoxy-imine nickel catalyst, which significantly enables the formation of linear ultrahigh molecular weight polyethylene (~5 brs/1000C, Mn = 1531 kDa) in a living polymerization (PDI = 1.08–1.11). An enhancement of 77 times on the polymer molecular weight occurs compared to the classical 2,6-diisopropyl substituted phenoxy-imine nickel catalyst. This avoids a tedious synthetic procedure and the use of an excess aluminum reagent as the activator and the scavenger.

Robust and Reactive Neutral Nickel Catalysts for Ethylene Polymerization and Copolymerization with a Challenging 1,1-Disubstituted Difunctional Polar Monomer

A series of methyl nickel complexes with phosphino-naphtholate chelate ligands have been strategically designed, synthesized, and fully characterized. These catalysts showed extremely high activity...

Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers

Several nickel complexes bearing sterically bulky phosphino-phenolate ([P,O]) ligands were synthesized and explored as catalysts for olefin (co)polymerization. In the absence of an activator, the complexes showed very high catalytic activities (up to 107 g molNi–1 h–1) for ethylene polymerization even at 90 °C or with the addition of a large amount of a polar additive (such as ethyl alcohol, diethyl ether, acetone, or even water), affording linear polymers with high molecular weights (up to 6.53 × 105). In contrast, most of the previously reported nickel catalysts suffer from severe activity suppression at elevated temperature. It is rare that a catalyst has so many good performances simultaneously, including high catalytic activity, good tolerance for polar groups, strong thermal stability, and yielding high molecular weight linear polyethylene. Most importantly, these bulky nickel complexes used in this study also effectively copolymerized ethylene with challenging polar vinyl monomers, including commer...

9,9-Dimethylxanthene-based binuclear phenoxy-imine neutral nickel(II) catalysts for ethylene homo- and copolymerization

Mononuclear neutral nickel catalyst Ni1 and binuclear complexes Ni2 and Ni3 based on rigid 9,9-dimethylxanthene frameworks featuring short Ni−Ni distances were synthesized, characterized and applied in ethylene (co)polymerization. Binuclear catalyst Ni2 exhibited higher activity in ethylene polymerization than corresponding mononuclear Ni1, and produce higher molecular weight polymer with a bimodal molecular weight distribution. Catalyst Ni2 is remarkably thermally robust, and still displaying promising activity at 93 °C. The polymer microstructure produced by Ni1 reveals a hyperbranched structure with a variety of branch types, while Ni2 product features methyl branches primarily. In the presence of comonomer 1,5-hexadiene, 1,7-octadiene, and methyl 10-undecenoate, mononuclear Ni1 suffers from either low catalytic activity or poor incorporation efficiency, while binuclear catalyst Ni2 effectively enchained these comonomers into the polymer chain, giving copolymer with unique microstructures.

Neutral Nickel Catalysts for Olefin Homo- and Copolymerization: Relationships between Catalyst Structures and Catalytic Properties.

Neutral Nickel Catalysts for Olefin Homo- and Copolymerization: Relationships between Catalyst Structures and Catalytic Properties.

Well-defined phosphino-phenolate neutral nickel(II) catalysts for efficient (co)polymerization of norbornene and ethylene.

Phosphino-phenolate neutral nickel catalysts 1-3/B(C6F5)3, without the help of any organoaluminum compound, were found to be efficient catalytic systems for norbornene polymerization and its copolymerization with norbornene derivatives. The amount of B(C6F5)3 required for achieving a high efficiency (3 equiv.) was markedly lower compared to previous reports, and high molecular weight polymers were obtained (>10(6) g mol(-1)). Efficient incorporation of polar monomers NBC, NBA, and NBM was also achieved in a controllable fashion, yielding high molecular weight copolymers. Catalysts 1-3 were highly active for ethylene polymerization as single component catalysts, with an activity of up to 10(7) g molNi(-1) h(-1), and catalyst 3 was more readily initiated at lower temperature. Catalysts 1-3 were also efficient in incorporating norbornene (up to 30%) into the polyethylene backbone. Bisligated phosphino-phenolate nickel complex 4 and salicylaldimine complex 5 were also studied for comparison, which further verified the unique performance of catalysts 1-3. Preliminary NMR analyses were conducted to explore the norbornene polymerization mechanism.

Effect of neutral nickel catalyst on cure process of silicon-containing polyarylacetylene

• The cure reactions of silicon-containing polyarylacetylene (PSA) were studied. • The cure temperature of the PSA markedly decreases with addition of catalyst. • The conversion ratio of terminal alkyne in the PSA is enhanced by adding catalyst. • The conversion ratio of internal alkyne in the PSA increases in the early stage. • The thermal stability of the catalyst cured PSA is retained. The curing behavior of silicon-containing polyarylacetylene (PSA) with nickel acetylacetonate and triphenylphosphine (Ni(acac) 2 /PPh 3 ) as a catalyst was studied by differential scanning calorimetry (DSC), FTIR in situ monitoring and gel time analysis. The thermal stability of the cured PSA was performed on thermogravimeter. The results show that the catalytic effect of Ni(acac) 2 /PPh 3 on curing reaction of PSA is distinct. The peak temperature of cure reaction of PSA was decreased by 100 °C when the catalyst was added into the resin at a molar ratio of 100:1. The conversion ratio of the terminal alkynes in PSA cured with the catalyst is higher than that cured without catalyst during heating. The internal alkynes in PSA are apt to achieve when the catalyst is added in the early stage of curing process. The apparent activation energy of the gel process of PSA with the catalyst declined about 30%. The catalyst-added PSA was cured at lower temperature. The temperature at 5% mass loss and residual yield at 800 °C in N 2 of the cured PSA with the catalyst-added and catalyst-free are 615 °C and 89%, 618 °C and 90%, respectively.

Self-immobilizing binuclear neutral nickel catalyst for ethylene polymerization: Synthesis and catalytic studies

A allyl-substituted salicylaldimine proligand (Scheme 1, Compound 5) was prepared by a condensation reaction, which reacted with trans-[NiCl(Ph)(PPh3)2] to give a binuclear neutral nickel (II) complex [((4-Allyl-2,6-iPr2C6H2) NCH)C6H3ONi(PPh3)Ph]2 (Scheme 1, Complex 6). The structure of the complex was characterized by 1H NMR, 13C NMR and elemental analysis. This novel complex bearing allyl groups can be used as a self-immobilizing catalyst for the polymerization of ethylene and does not need a cocatalyst for their catalytic performance. The self-immobilizing catalytic systems not only possess high activity (up to 5.23×105g of PE/(mol of Nih)) but also can produce high-molecular-weight polyethylenes (Mw=(0.42–0.71)×106) with relatively broad molecular weight distributions (MWD=2.83–3.11). According to the 13C NMR analyses, the resultant polyethylenes contain a few branched chains mainly consisting of methyl branches.

Ethylene Homo- and Copolymerization by Single Component Phosphinophenolate Neutral Nickel Catalysts

Ethylene Homo- and Copolymerization by Single Component Phosphinophenolate Neutral Nickel Catalysts

Accessible, Highly Active Single-Component β-Ketiminato Neutral Nickel(II) Catalysts for Ethylene Polymerization

A series of novel neutral nickel complexes based on cyclic β-ketiminato ligands, [(2,6-iPr2C6H3)N═CHC6H8O]Ni(Ph)(PPh3) (3b), [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(Ph)(PPh3) (6a−c), and [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(CH3)(Py) (7a−c: a, n = 0; b, n = 1; c, n = 2) have been synthesized and characterized. These conveniently accessible complexes proved to be highly active catalysts for ethylene polymerization without an activator. Under the optimized conditions, an activity of 71.4 kg of PE/((mol of Ni) h atm) was observed using 6c as a catalyst. Particularly, it is of great interest that a bulky substituent proximate to the oxygen atom of the β-ketiminato complex is no longer a prerequisite to attain high catalytic efficiency, which is much different from the case for salicylaldiminato neutral nickel catalysts. This is effectively supported by the lower activation enthalpy changes of complexes 3b and 6a−c relative to values for the classic salicylaldiminato complexes. Moreover, for complexes 6a−c and 7a−c, the degree of conjugation between the phenylene ring and the corresponding nickel chelate of the complex can be tuned via changes in the ligand structure, which remarkably influence the molecular weights and the microstructures of the resulting polyethylenes. In comparison with the highly conjugated complexes 6a and 7a, complexes 6b,c and 7b,c, with a low degree of conjugation, produced polyethylenes with much higher molecular weights and lower branch contents. X-ray crystallographic analysis of 3b and 6a−c provides detailed information about the differences among these structures, and various typical angles and bond distances produce evidence of the conjugation modulation effect.

The mechanism of ethylene polymerization by nickel salicylaldiminato catalysts – Agostic interactions and their kinetic isotope effects

The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene–alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect ( k H/ k D = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active.

Synthesis, molecular structures and norbornene addition polymerization activity of the neutral nickel catalysts supported by N-naphthyl-salicylaldiminato ligands

A series of nickel Schiff-base complexes were synthesized by the reaction of Schiff-bases containing N-naphththyl group with trans-[Ni(PPh 3) 2(Ph)Cl] and they were characterized by EA, IR and NMR. When activated by methylaluminoxane, these complexes exhibit good catalytic activity for the addition polymerization of norbornene.

Synthesis, Molecular Structures, and Norbornene Addition Polymerization Activity of the Neutral Nickel Catalysts Supported by β-Diketiminato [N, N], Ketiminato [N, O], and Schiff-Base [N, O] Ligands

A series of neutral nickel complexes [Ni(Ph)(PPh3)(N, O)] with Schiff-base ligands (N, O) [N, O = 5-Me-3-tert-Bu-(Ar−NCH)C6H2O (1, Ar = 2,6-Me2C6H3; 2, Ar = 2,6-i-Pr2C6H3)], [Ni(Ph)(PPh3)(N,O)], with β-ketiminato ligands (N, O) [N, O = CH3COCHC(CH3)N−Ar (3, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3)] and [Ni(N, N)(PPh3)], and with β-diketiminato ligands (N, N) [5, N, N = [2,6-i-Pr2(C6H3)NC(CH3)]2CH] have been synthesized and characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by X-ray single-crystal analyses. Although their ligands have similar structures, complex 4 possesses a structure similar to that of four-coordination nickel with complex 1, while complex 5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic activities of up to 3.16 × 107 g PNB mol-1 Ni h-1 for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polyborbornene have been investigated under various reaction conditions.

Ethylene Polymerization Catalyzed by Neutral Nickel(II) Complex with O^N-Chelating Ligand

We have achieved the synthesis of neutral nickel catalyst with the modified O^ N-chelating ligand for the ethylene polymerization. The activity of the catalyst, and the molecular weight and the branching structure of the polymer obtained strongly depend on the ligand structure as well as the presence of Ni(COD)2 which is used as an activator. The crystal structure of the catalyst was determined and the long nickel-phosphine bond length seems to play an important role for increasing the polymerization activity.

Ethylene Polymerization by Self‐Immobilized Neutral Nickel Catalysts Bearing Allyl Groups

Abstract[Ni(Ph)(PPh3)(N,O)] complexes containing phenylimino‐phenolato ligands (N,O) (1: N,O = A; 2: N,O = B; 3: N,O = C; 4: N,O = D; 5: N,O = E) have been synthesized and characterized. The molecular structure of 4 was determined by single‐crystal X‐ray analysis. Complexes 2−5 bearing allyl groups have been investigated as self‐immobilized catalysts for ethylene polymerization without the use of co‐catalysts. The high ethylene polymerization activities of ca. 105 g·PE mol−1 Ni·h−1 and high molecular weight (Mw ≈︁ 105) of polyethylene could be accomplished by changing the ligand structures and reaction conditions. The self‐immobilization of catalysts brings about a dramatic increase in the catalytic activities of ethylene polymerization. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)