Mechanism of Organoscandium-Catalyzed Ethylene Copolymerization with Amino-Olefins

A Quantum Chemical Analysis

Jiazhen Chen, Alessandro Motta, Jialong Zhang, Yanshan Gao, Tobin J Marks

Research output: Contribution to journalArticle

Abstract

The direct, efficient copolymerization of ethylene with polar monomers represents a "holy grail" for the synthesis of polar polyethylenes; however, developing effective catalysts for such copolymerizations remains a largely unsolved challenge. Very recently, organoscandium catalysts were shown to be very active for ethylene + polar monomer [H2Câ• CH(CH2)nCH2FG, FG = polar functional group] copolymerization. Interestingly, comonomer enchainment selectivity decreases with increasing linker length (n), while overall polymerization activity is largely unaffected, and the intriguing mechanistic origins are not yet understood. In this study, density functional theory (DFT) methods are employed to investigate the mechanism of organoscandium-catalyzed ethylene + amino olefin (AO) copolymerization, using (C5Me4SiMe3)Sc(CH2CH2CH3)+B(C6F5)4 - (Sc-1) as the model active species and N-(1-butenyl)nPr2 and N-(1-octenyl)nPr2 as model comonomers. Among conceivable scenarios in monomer coordination, activation, and insertion, it is found that copolymerization activity is largely governed by intermolecular amino olefin N-coordination. Amino olefin n-dependent enchainment patterns arise from chain-length regulation of the energy barrier for an amino olefin chelating "self-assisted" enchainment pathway. Short-chain N-(1-butenyl)nPr2 enchains via a self-assisted insertion pathway (6.0 kcal/mol energy barrier), while long-chain N-(1-octenyl)nPr2 enchains via unassisted 1,2-insertion with exogenous amine coordination (7.2 kcal/mol energy barrier). These findings explain the experimental results, showcase the characteristic reactivity of Sc catalysts in polar monomer copolymerization, and highlight the potential and challenges in developing catalysts for polar monomer copolymerization.

Original languageEnglish
Pages (from-to)8810-8818
Number of pages9
JournalACS Catalysis
DOIs
Publication statusAccepted/In press - Jan 1 2019

Fingerprint

Alkenes
Copolymerization
Olefins
Ethylene
Monomers
Chemical analysis
Energy barriers
Catalysts
Polyethylenes
Chelation
ethylene
Chain length
Functional groups
Amines
Density functional theory
Chemical activation
Polymerization

Keywords

  • amino olefin
  • DFT
  • olefin polymerization
  • polar monomer
  • scandium

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Cite this

Mechanism of Organoscandium-Catalyzed Ethylene Copolymerization with Amino-Olefins : A Quantum Chemical Analysis. / Chen, Jiazhen; Motta, Alessandro; Zhang, Jialong; Gao, Yanshan; Marks, Tobin J.

In: ACS Catalysis, 01.01.2019, p. 8810-8818.

Research output: Contribution to journalArticle

Chen, Jiazhen ; Motta, Alessandro ; Zhang, Jialong ; Gao, Yanshan ; Marks, Tobin J. / Mechanism of Organoscandium-Catalyzed Ethylene Copolymerization with Amino-Olefins : A Quantum Chemical Analysis. In: ACS Catalysis. 2019 ; pp. 8810-8818.
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abstract = "The direct, efficient copolymerization of ethylene with polar monomers represents a {"}holy grail{"} for the synthesis of polar polyethylenes; however, developing effective catalysts for such copolymerizations remains a largely unsolved challenge. Very recently, organoscandium catalysts were shown to be very active for ethylene + polar monomer [H2C{\^a}• CH(CH2)nCH2FG, FG = polar functional group] copolymerization. Interestingly, comonomer enchainment selectivity decreases with increasing linker length (n), while overall polymerization activity is largely unaffected, and the intriguing mechanistic origins are not yet understood. In this study, density functional theory (DFT) methods are employed to investigate the mechanism of organoscandium-catalyzed ethylene + amino olefin (AO) copolymerization, using (C5Me4SiMe3)Sc(CH2CH2CH3)+B(C6F5)4 - (Sc-1) as the model active species and N-(1-butenyl)nPr2 and N-(1-octenyl)nPr2 as model comonomers. Among conceivable scenarios in monomer coordination, activation, and insertion, it is found that copolymerization activity is largely governed by intermolecular amino olefin N-coordination. Amino olefin n-dependent enchainment patterns arise from chain-length regulation of the energy barrier for an amino olefin chelating {"}self-assisted{"} enchainment pathway. Short-chain N-(1-butenyl)nPr2 enchains via a self-assisted insertion pathway (6.0 kcal/mol energy barrier), while long-chain N-(1-octenyl)nPr2 enchains via unassisted 1,2-insertion with exogenous amine coordination (7.2 kcal/mol energy barrier). These findings explain the experimental results, showcase the characteristic reactivity of Sc catalysts in polar monomer copolymerization, and highlight the potential and challenges in developing catalysts for polar monomer copolymerization.",
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