Phosphine-sulfonate Palladium Research Articles

Synthesis of partially fluorinated polyolefins via copolymerization of ethylene with fluorinated norbornene-based comonomers

Partially fluorinated polyolefins were efficiently synthesized through copolymerization of ethylene with fluorinated norbornene-based comonomers using phosphine–sulfonate palladium catalysts.

Enhanced mechanical properties of acrylate and 5-vinyl-2-norbornene-based ethylene terpolymers: rational design and synthesis using remotely modulated phosphine–sulfonate palladium complexes

From a practical perspective, it is important to maintain or increase the mechanical properties of functional ethylene copolymers to those of nonpolar polyethylene (PE).

Efficient copolymerization of ethylene with norbornene mediated by phosphine-sulfonate palladium catalysts

A series of tBu-/Ar-substituted phosphine-sulfonate palladium catalysts Pd1-Pd6 {[κ2(P, O)-(tBu)ArP(C6H4SO2O)]Pd(Me)(DMSO)} (1: Ar = Ph; 2: Ar = 4-OMe-C6H4; 3: Ar = 4-CF3-C6H4; 4: Ar = 2-OMe-C6H4; 5: Ar = 2,5- (OMe)2-C6H3; 6: Ar = 2,4-(OMe)2-C6H3) were prepared to copolymerize ethylene with norbornene and its polar derivatives. Installing electron-donating OMe substituent on the nonchelating P-bound aryl was proven to enhance the properties of catalysts. The position and number of OMe substituent significantly influenced the copolymerization results. The E-NB copolymers generated from these catalysts showed both high comonomer incorporations (≥19.3 mol%) and high copolymer molecular weights (≥24.6 kg⋅mol−1), which has been proven to be difficult to achieve using this catalyst system. And for the obtained copolymers, their norbornene incorporations and Tg values conformed to a linear relationship. More importantly, these catalysts can efficiently mediate the copolymerizations of ethylene and polar norbornenes, along with high activities (up to 1.0 × 106 g⋅mol−1⋅h−1), high molecular weights (up to 182 kg⋅mol−1), and high incorporations (up to 36.7 mol%). This work provided an efficient method to synthesis cyclic olefin copolymer using late transition metal catalysts.

A DFT Study of the Copolymerization of Methyl Vinyl Sulfone and Ethylene Catalyzed by Phosphine–Sulfonate and α-Diimine Palladium Complexes

Density functional theory (DFT) calculations were comparatively carried out to reveal the origins of different catalytic performances from phosphine–benzene sulfonate (A, [{P^O}PdMe(L)] (P^O = Κ2-P,O-Ar2PC6H4SO3 with Ar = 2-MeOC6H4)) and α-diimine (B, [{N^N}PdMe(Cl)] (N^N = (ArN=C(Me)-C(Me)=NAr) with Ar = 2,6-iPr2C6H3)) palladium complexes toward the copolymerization of ethylene and methyl vinyl sulfone (MVS). Having achieved agreement between theory and experiment, it was found that the favorable 2,1-selective insertion of MVS into phosphine–sulfonate palladium complex A was due to there being less structural deformations in the catalyst and monomer. Both the MVS and ethylene insertions were calculated, and the former was found to be more favorable for chain initiation and chain propagation. In the case of α-diimine palladium system B, the resulting product of the first MVS insertion was quite stable, and the stronger O-backbiting interaction hampered the insertion of the incoming ethylene molecule. These computational results are expected to provide some hints for the design of transition metal copolymerization catalysts.

Polar-Functionalized Polyethylenes Enabled by Palladium-Catalyzed Copolymerization of Ethylene and Butadiene/Bio-Based Alcohol-Derived Monomers.

Polar-functionalized polyolefins are high-value materials with improved properties. However, their feedstocks generally come from non-renewable fossil products; thus, it requires the development of renewable bio-based monomers to produce functionalized polyolefins. In this contribution, via the Pd-catalyzed telomerization of 1,3-butadiene and three types of bio-based alcohols (furfuryl alcohol, tetrahydrofurfuryl alcohol, and solketal), 2,7-octadienyl ether monomers including OC8-FUR, OC8-THF, and OC8-SOL were synthesized and characterized, respectively. The copolymerization of these monomers with ethylene catalyzed by phosphine-sulfonate palladium catalysts was further investigated. Microstructures of the resultant copolymers were analyzed by NMR and ATR-IR spectroscopy, revealing linear structures with incorporations of difunctionalized side chains bearing both allyl ether units and polar cyclic groups. Mechanical property studies exhibited better strain-at-break of these copolymers compared to the non-polar polyethylene, among which the copolymer E-FUR with the incorporation of 0.3 mol% displayed the highest strain-at-break and stress-at-break values of 940% and 35.9 MPa, respectively.

Exploring steric effect of electron-donating group in palladium and nickel mediated ethylene polymerization and copolymerization with polar monomers

The influence of steric effect of electron-donating substituents on the phosphine-sulfonate palladium and nickel catalysts was rarely studied in olefin (co)polymerizations. In this contribution, a family of flexible cyclohexyl/rigid aromatic phosphine-sulfonate palladium and nickel catalysts was designed, synthesized, and comprehensively identified by varying number, position, and size of alkoxy groups on aromatic substituents of phosphine. In ethylene polymerization, the steric effect of alkoxy substituents in palladium and nickel catalysts plays an important role on tuning polymer molecular weight, which gives the high molecular weight of 380 kg mol−1 at 80 °C in the palladium system and also provides very high catalytic activity of 16000 kg mol-1 h−1 at 70 °C in the nickel system. In ethylene copolymerization with polar monomers, the decrease of steric bulk leads to an increase on the co-monomer incorporation in the obtained copolymers. As a result, the copolymerization of ethylene with methyl acrylate, and acrylic acid using palladium catalysts affords the high incorporation of 9.5 mol% and 8.3 mol%, respectively; and the nickel promoted ethylene copolymerization with vinyl trimethoxysilane, and 6-chloro-1-hexene gives the incorporation of 3.7 mol% and 5.0 mol%, respectively.

A disubstituted-norbornene-based comonomer strategy to address polar monomer problem

The transition-metal-catalyzed copolymerization of olefins with polar comonomers is a direct strategy to access polar-functionalized polyolefins in an economical manner. Due to the intrinsic poisoning effect of polar groups towards Lewis acidic metal centers and the drastic reactivity differences of polar comonomers versus non-polar olefins, it is challenging to develop catalysts that provide the desired polymer molecular weight, comonomer incorporation, and activity. In this contribution, we tackle this issue from a comonomer perspective using 5,6-disubstituted norbornenes, which are highly versatile, easily accessible, inexpensive, and capable of introducing two functional groups in a single insertion. More importantly, they are only mildly poisoning due to the presence of long spacers between double bonds and polar groups, and are not prone to β-hydride elimination due to their cyclic structures. As strong π-donors, they can competitively bind to metal centers versus olefins. Indeed, phosphine-sulfonate palladium catalysts can catalyze the copolymerization of ethylene with 5,6-disubstituted norbornenes and simultaneously achieve a high polymerization activity, copolymer molecular weight, and comonomer incorporation. The practicality of this system was demonstrated by studying the properties of the resulting polymers, copolymerization in hydrocarbon solvents or in bulk, recovery/utilization of unreacted comonomer, molecular weight modulation, and large-scale synthesis.

Computational study of the copolymerization mechanism of ethylene with methyl 2-acetamidoacrylate catalyzed by phosphine-sulfonate palladium complexes

In this research, a computational study is carried out to describe the insertion of a vital monomer, methyl 2-acetamidoacrylate (MAAA), into catalyst A (A = [(POOMe,OMe)PdMe]) (POOMe,OMe = 2[2-MeOC6H4](2-SO3-5-MeC6H4)P).

Catalyst deconstructs polyethylene, producing valuable alkanes

The influence of steric effect of electron-donating substituents on the phosphine-sulfonate palladium and nickel catalysts was rarely studied in olefin (co)polymerizations. In this contribution, a family of flexible cyclohexyl/rigid aromatic phosphine-sulfonate palladium and nickel catalysts was designed, synthesized, and comprehensively identified by varying number, position, and size of alkoxy groups on aromatic substituents of phosphine. In ethylene polymerization, the steric effect of alkoxy substituents in palladium and nickel catalysts plays an important role on tuning polymer molecular weight, which gives the high molecular weight of 380 kg mol−1 at 80 °C in the palladium system and also provides very high catalytic activity of 16000 kg mol-1 h−1 at 70 °C in the nickel system. In ethylene copolymerization with polar monomers, the decrease of steric bulk leads to an increase on the co-monomer incorporation in the obtained copolymers. As a result, the copolymerization of ethylene with methyl acrylate, and acrylic acid using palladium catalysts affords the high incorporation of 9.5 mol% and 8.3 mol%, respectively; and the nickel promoted ethylene copolymerization with vinyl trimethoxysilane, and 6-chloro-1-hexene gives the incorporation of 3.7 mol% and 5.0 mol%, respectively.

Mechanistic Studies for Palladium Catalyzed Copolymerization of Ethylene with Vinyl Ethers.

The mechanism of ethylene with vinyl ether (VE, CH2=CHOEt) copolymerization catalyzed by phosphine-sulfonate palladium complex (A) was investigated by density functional theory (DFT) calculation. On achieving an agreement between theory and experiment, it is found that the favorable 1,2-selective insertion of VE into the complex A originates from stronger hydrogen interaction between the oxygen atom of VE and the ancillary ligand of catalyst A. Additionally, VE insertion is easier into the ethylene pre-inserted intermediate than that into the catalyst to form the resultant copolymers with the major units of OEt in chain and minor units of OEt at the chain end. The effect of β-OEt and β-H elimination was explored to elucidate chain termination and the molecular weight of copolymers. Furthermore, a family of cationic catalysts has been demonstrated to copolymerize ethylene with VE along with our modified cationic complex B with higher incorporation of VE and reactivity in comparison with complex A, which was modelled computationally by increasing the strong interactions between the catalyst and monomer moiety. Other than VE, the activity of cationic complex B for copolymerization of vinyl chloride and methacrylate is also computed successfully.

A comprehensive picture on catalyst structure construction in palladium catalyzed ethylene (co)polymerizations

Late transition metal palladium catalysts chelated by benchmark α-diimine, phosphine-sulfonate, bisphosphine-monoxide ligands are of great interest for ethylene polymerization and challenging copolymerization with polar comonomers. Compared to numerous studies on the classic α-diimine and phosphine-sulfonate palladium catalysts, the new generation bisphosphine-monoxide palladium (BPMO-Pd) system is far less investigated. In this contribution, by skillfully designing a family of BPMO-Pd catalysts bearing differed steric and electronic P(III) phosphine groups, differed steric and electronic O = P(V) phosphine monoxide groups, and different connectivity of them, a comprehensive picture on catalyst structure construction is built for ethylene (co)polymerizations. This constructed catalyst structure-polymerization property relationship paves the way for the development of more efficient late transition metal catalysts for olefin (co)polymerization.

Ligand–metal secondary interactions in phosphine–sulfonate palladium and nickel catalyzed ethylene (co)polymerization

Ligand secondary interactions and Lewis acid modulation are simultaneously achieved in palladium and nickel catalyzed ethylene polymerization and copolymerization.

Origin of different chain-end microstructures in ethylene/vinyl halide copolymerization catalysed by phosphine–sulfonate palladium complexes

Ethylene and vinyl halide (VX, X = F or Cl) copolymerization mechanism in the presence of catalysts A ((POOMe,OMe)PdMe, POOMe,OMe = {2(2-MeOC6H4)(2-SO3-5-MeC6H3)P}) and A′ ((POBp,OMe)PdMe, POBp,OMe = {(2-MeOC6H4)(2-{2,6-(MeO)2C6H3}C6H4)(2-SO3-5-MeC6H3)P}) has been comparatively studied via density functional theory (DFT) calculations.

Diphosphazane-monoxide and Phosphine-sulfonate Palladium Catalyzed Ethylene Copolymerization with Polar Monomers: A Computational Study

Density functional theory (DFT) calculations have been comparatively carried out to disclose the origin of different catalytic performance of diphosphazane-monoxide and phosphine-sulfonate palladium complexes toward copolymerization of ethylene and vinyl polar monomers. A theoretical comparison of the two catalytic systems indicates that the rigid five-membered backbone and cationic nature of the diphosphazane-monoxide palladium complex are beneficial for its copolymerization activity. Having achieved agreement between theory and experiment, it is found that the favorable 2,1-selective insertion of methyl methacrylate (MMA) into the diphosphazane-monoxide palladium complex originates from less geometrical deformation and the MeO···H interaction between the ancillary ligand and the methyl of MMA. In this catalyst system, it is kinetically difficult for the MMA pre-enchained species to undergo subsequent ethylene insertion due to the steric repulsion between the methyl of MMA and the inserting ethylene moie...

Sterically very bulky aliphatic/aromatic phosphine-sulfonate palladium catalysts for ethylene polymerization and copolymerization with polar monomers

Copolymerization of ethylene and polar monomers with significantly high molecular weight and activity was achieved using bulky aliphatic/aromatic phosphine-sulfonate palladium catalysts.

Direct Synthesis of Polar-Functionalized Linear Low-Density Polyethylene (LLDPE) and Low-Density Polyethylene (LDPE)

Late-transition-metal catalysts have great potentials to incorporate polar comonomers during olefin polymerization. The preparation of polar-functionalized polyolefins with different microstructures and topologies is a highly fascinating concept. In this contribution, we demonstrate this possibility through palladium-catalyzed ethylene copolymerizations with polar-functionalized α-olefins and their terpolymerizations with α-olefins. A phosphine–sulfonate–palladium catalyst (PO-Pd) afforded highly linear polyethylene during ethylene homopolymerization. Linear low-density polyethylene (LLDPE) was obtained from the PO-Pd-catalyzed copolymerizations of ethylene with α-olefins; in these copolymerizations, the partial or complete replacement of α-olefins with polar-functionalized α-olefins led to the formation of polar-functionalized LLDPE (P-LLDPE). A specially designed α-diimine palladium catalyst (NN-Pd) afforded polyethylenes with tunable branching densities (16–37 per 1000 carbon atoms), melting points (10...

Influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization. This type of catalyst features six-membered chelate ring size, and can enable the copolymerizations of ethylene with a wide variety of polar monomers. In this contribution, we decide to investigate the influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts. As such, a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II) complexes [ κ 2-( P , O )-2-(CH2- P R1R2)-4-methylphenyl-sulfonato]Pd(Me) (DMSO) ( Pd1 , R1=R2=Cy, Pd2 , R1=R2= o -MeO-C6H4; Pd3 , R1=Ph, R2=2-[2,6-(MeO)2C6H3]C6H4; DMSO=dimethyl sulfoxide) were designed, prepared and characterized. These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether. However, their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2 ′. The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.

Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization.

The transition-metal-catalyzed copolymerization of olefins with polar functionalized co-monomers represents a major challenge in the field of olefin polymerization. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer molecular weight through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine-sulfonate palladium and nickel catalysts, and its influence on ethylene polymerization and copolymerization is investigated. In ethylene polymerization, this strategy leads to enhanced activity, catalyst stability, and increased polyethylene molecular weight. In ethylene copolymerization with polar monomers, improvements in all copolymerization parameters are realized. This effect is most significant for polar monomers with hydrogen-bond-donating abilities.

Side-Arm Control in Phosphine-Sulfonate Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization

A series of phosphine-sulfonate ligands bearing various side-arm substituents were designed and prepared. The corresponding Pd(II) complexes [κ2-(P,O)-2-(PPhAr)-1-benzenesulfonato]Pd(Me)(dmso) (Pd1, Ar = o-MeO-C6H4; Pd2, Ar = o-PhO-C6H4; Pd3, Ar = o-(2,6-Me2-C6H3)O-C6H4; Pd4, Ar = o-PhSO2-C6H4) and Ni(II) complexes [κ2-(P,O)-2-(PPhAr)-1-benzenesulfonato]NiPh(PPh3) (Ni1, Ar = o-MeO-C6H4; Ni2, Ar = o-PhO-C6H4; Ni3, Ar = o-(2,6-Me2-C6H3)O-C6H4; Ni4, Ar = o-PhSO2-C6H4) were prepared and applied in ethylene polymerization and ethylene–polar monomer copolymerization. Catalysts Pd2, Pd3, Ni2, and Ni3 are moderately active in ethylene polymerization (activity up to 8.7 × 105 g mol–1 h–1), generating polyethylene with high molecular weights (Mn up to 105100) and high melting temperatures (Tm up to 131.6 °C). The two palladium catalysts can also initiate efficient copolymerization of ethylene with methyl acrylate, allyl cyanide, and allyl acetate. Most importantly, high copolymer molecular weights (Mn between 21600...

Redox Control in Olefin Polymerization Catalysis by Phosphine–Sulfonate Palladium and Nickel Complexes

Two phosphine–sulfonate ligands, bearing both the ferrocene and the bi‐aryl units, were prepared and characterized. The corresponding palladium and nickel complexes are active in ethylene polymerization. In both the palladium and the nickel systems, the oxidation of the ferrocene unit leads to a decrease in catalytic activities and the polymer molecular masses. Interestingly, the neutral palladium catalyst is not active for norbornene polymerization, while the oxidized analogue shows good activity. As such, switchable polymerization could be achieved.