Cationic P,O‐Coordinated Nickel(II) Catalysts for Carbonylative Polymerization of Ethylene: Unexpected Productivity via Subtle Electronic Variation

Abstract

Transition‐metal‐catalyzed copolymerization of ethylene with carbon monoxide affords polyketones materials with excellent mechanical strength, photodegradability, surface and barrier properties. Unlike the widely used and rather expensive Pd catalysts, Ni‐catalyzed carbonylative polymerization is very difficult since the strong binding affinity of CO to Ni deactivates the highly electrophilic metal center easily. In this study, various cationic P,O‐coordinated Ni complexes were synthesized using the electronic modulation strategy, and the catalyst with strong electron‐donating substituents exhibits an excellent productivity of 104 g polymer (g Ni)−1, which represents a rare discovery that a Ni complex could operate with such exceptional efficiency in comparison with Pd catalysts. Notably, those Ni catalysts were also efficient for terpolymerization of ethylene, propylene with CO for producing commercial polyketone materials with low melting temperatures and easy processibility.

Favorable Propylene-Incorporated Terpolymerization of Ethylene with CO Mediated by Cationic [P,O]-Pd and Ni Complexes

“…Inspired by the wide spectrum of tunable positions at phosphine, amine, and phosphine oxide moieties in diphosphazane monoxide (PNPO) ligands, various Pd and Ni complexes were designed based on electronic and steric modulation (Figure ), which can be prepared easily in a modular fashion with good yields. − Initially, the study focused on a cationic PNPO-Pd-catalyzed terpolymerization of propylene and ethylene with CO at 90 °C (Table ). In a typical polymerization, 10 μmol of Pd 1 and 1.5 equiv of sodium tetrakis (3,5-bis­(trifluoromethyl)­phenyl)­borate (NaBArF) activator were dissolved in 10 mL of toluene and a pressure of ∼0.2 MPa of propylene (measured by weight, ∼0.5 g) was applied, and C 2 H 4 /CO (1:1) gas mixture was introduced into the autoclave to reach a pressure of 3.0 MPa to start the polymerization.…”

“…In comparison with diphosphine-coordinated Pd, a Ni catalyst has been rarely investigated for terpolymerization, and a representative Ni­(diEt-AXPHOS)­(OTf) 2 exhibited a C3/C2 consumption rate of about 0.01 . Inspired by the excellent catalytic performance in terms of reactivity and molecular weight control in ethylene/polar vinyl monomer and ethylene/CO copolymerization observed for the Pd- and Ni-coordinated diphosphazane monoxide (PNPO) ligands, − we have applied the single-site catalysts to the terpolymerization of ethylene and α-olefin with CO. In particular, the electronic and steric nature of the substituents on phosphine, amine, and phosphine oxide moieties in the PNPO platform is systematically investigated, in which the installation of an aliphatic structure on amine moieties provides highly active Pd catalysts.…”

Mechanistic Insights into Cationic [P,O]-Pd-Catalyzed Chain-Transfer Copolymerization of Ethylene with Carbon Monoxide

“…The MALDI-TOF-MS spectrum suggests the formation of diester end groups via [Ni−OMe] + species, similar to the [P,O]-Pd system. As such a cost-effective nickel catalyst exhibited a high productivity toward carbonylative polymerization of ethyl-ene, 44 the regulation of molecular weight via chain-transfer polymerization enables it to be a promising candidate for industrial applications.…”

“…We discovered a series of cationic diphosphazane monoxide-coordinated palladium/nickel complexes ([P,O]-Pd/Ni) based on the electronic and steric modulation strategy , for the highly efficient copolymerization of ethylene with CO, affording alternating polyketone, nonalternating polyketone, , and in-chain ketone polyethylene materials, and [P,O]-Ni exhibited a remarkable productivity of 31150 g PK/g Ni . However, nonprotonic solvents are generally required for this [P,O]-type catalyst, and the polymerization features low initiation efficiency and a lower tendency for chain transfer, thus yielding high-molecular-weight polyketones. − Concerning the specific role of methanol in the diphosphine–Pd catalyst system, we investigated the feasibility of chain transfers and the deactivation/reactivation pathways toward [P,O]-Pd/Ni-catalyzed copolymerization in methanol using the state-of-the-art electrospray ionization mass spectrometry (ESI-MS) (Figure ). The presence of chain transfer regulated the molecular weight values of the resulting polyketones within the range of 8.13–238 kg/mol, and more than two times higher productivity was obtained with 1,4-benzoquinone (BQ) additives.…”

Influence of Silica-Supported Alkylaluminum on Heterogeneous Zwitterionic Anilinonaphthoquinone Nickel and Palladium-Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

“…Polyolefins are a family of widely used polymeric materials with rapid development and huge production in the current plastics industry. − The introduction of a very small amount of polar functional groups on the nonpolar polyolefin backbone can significantly improve the properties of polyolefins, and it is highly challenging to achieve such functionalized materials through the direct coordination copolymerization of olefin and polar monomers . Palladium- and nickel-based late transition metal catalysts have developed rapidly in recent years due to their lower electrophilicity compared with early transition metal catalysts and thus have gained superiority in catalyzing the direct copolymerization of olefin and polar monomers to produce functional polyolefins. − However, it is rather difficult to achieve the industrial production of functional polyolefins using homogeneous late transition metal catalysts due to some serious shortcomings, such as uncontrolled polymer morphology and serious reactor fouling. The heterogenization of homogeneous late transition metal catalysts has been considered as a promising pathway to overcome the above problems. − …”