Pyridylamido Bi-Hafnium Olefin Polymerization Catalysis

Conformationally Supported Hf⋯Hf Enchainment Cooperativity

Yanshan Gao, Aidan R. Mouat, Alessandro Motta, Alceo Macchioni, Cristiano Zuccaccia, Massimiliano Delferro, Tobin J Marks

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 Å, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 Å). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.

Original languageEnglish
Pages (from-to)5272-5282
Number of pages11
JournalACS Catalysis
Volume5
Issue number9
DOIs
Publication statusPublished - Jul 27 2015

Fingerprint

Hafnium
Alkenes
Catalysis
Olefins
Ethylene
Ligands
Polymerization
Metals
Chemical activation
Nuclear magnetic resonance
Structural dynamics
Polyethylene
Aniline
Naphthalene
Homopolymerization
Discrete Fourier transforms
Pyridine
Copolymerization
Nuclear magnetic resonance spectroscopy
Polyethylenes

Keywords

  • bimetallic
  • cooperativity effects
  • hafnium
  • NMR spectroscopy
  • olefin polymerization

ASJC Scopus subject areas

  • Catalysis

Cite this

Pyridylamido Bi-Hafnium Olefin Polymerization Catalysis : Conformationally Supported Hf⋯Hf Enchainment Cooperativity. / Gao, Yanshan; Mouat, Aidan R.; Motta, Alessandro; Macchioni, Alceo; Zuccaccia, Cristiano; Delferro, Massimiliano; Marks, Tobin J.

In: ACS Catalysis, Vol. 5, No. 9, 27.07.2015, p. 5272-5282.

Research output: Contribution to journalArticle

Gao, Yanshan ; Mouat, Aidan R. ; Motta, Alessandro ; Macchioni, Alceo ; Zuccaccia, Cristiano ; Delferro, Massimiliano ; Marks, Tobin J. / Pyridylamido Bi-Hafnium Olefin Polymerization Catalysis : Conformationally Supported Hf⋯Hf Enchainment Cooperativity. In: ACS Catalysis. 2015 ; Vol. 5, No. 9. pp. 5272-5282.
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abstract = "Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 {\AA}, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 {\AA}). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.",
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AU - Motta, Alessandro

AU - Macchioni, Alceo

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N2 - Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 Å, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 Å). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.

AB - Homobimetallic Hf(IV) complexes, L2-Hf2Me5 (3) and L2-Hf2Me4 (4) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), were synthesized by reaction of the free ligand L2 with the appropriate Hf precursor and were characterized in solution (NMR) and in the solid state (X-ray diffraction). In 3, L2 acts as a dianionic tridentate ligand for one Hf metal center and as a monoanionic bidentate ligand for the other, whereas in 4, both Hf units are tricoordinated to opposite sides of L2. In the solid state, the Hf···Hf distance is significantly different in 3 vs 4 (6.16 vs 8.06 Å, respectively), but in solution, the structural dynamics of the two linked metallic units in bis-activated complex 3 accesses conformers with far closer Hf···Hf distances (∼3.2 Å). Once activated with Ph3C+B(C6F5)4- (B1) or PhNMe2H+B(C6F5)4- (NB), 3 exhibits pronounced bimetallic cooperative effects in ethylene homopolymerization and ethylene +1-octene copolymerization vs the monometallic analogue L1-HfMe2 (1, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline) and bimetallic 4, producing polyethylene with 5.7 times higher Mw and poly(ethylene-co-1-octene) with 2.4 times higher Mw and 1.9 times greater 1-octene enchainment densities than 1. The activation chemistry of 3 and 4 with 1 or 2 equiv of B1 and NB is characterized in detail by NMR spectroscopy. In sharp contrast to 1, which undergoes Hf-Cnaph protonolysis followed by naphthyl remetalation with NB as the cocatalyst, activation of 3 with B1 or NB proceeds by consecutive -CH3 protonolysis/abstractions at each Hf center, explaining the higher polymerization activity of 3/NB versus 1/NB. All product polymers have narrow (2-3) PDIs, and this is explained by NMR evidence for very fast exchange of alkyl moieties between the two active Hf metal centers. Key experimental findings are supported by DFT analysis.

KW - bimetallic

KW - cooperativity effects

KW - hafnium

KW - NMR spectroscopy

KW - olefin polymerization

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