Alumina as a simultaneous support and CO catalyst: Cationic hafnium complex evidenced by experimental and DFT analyses

Marco Delgado; Catherine C. Santini; Françoise Delbecq; Raphaël Wischert; Boris Le Guennic; Géraldine Tosin; Roger Spitz; Jean Marie Basset; Philippe Sautet

doi:10.1021/jp104999n

Alumina as a simultaneous support and CO catalyst: Cationic hafnium complex evidenced by experimental and DFT analyses

Marco Delgado, Catherine C. Santini, Françoise Delbecq, Raphaël Wischert, Boris Le Guennic, Géraldine Tosin, Roger Spitz, Jean Marie Basset, Philippe Sautet

Physical Sciences and Engineering

Research output: Contribution to journal › Article › peer-review

22 Scopus citations

Abstract

Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH₂tBu)4, 1, on y-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl-metal bonds: Hf-CH₂tBu and Al-CH ₂tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [(≡Al_IVO) Hf(CH₂tBu)₃], a neutral bis-aluminoxy [(≡Al _IVO)(Al_sO)Hf(CH₂tBu)₂], and a zwitterionic bis-aluminoxy complex [(≡Al_IVO)(Al _sO)Hf(CH₂tBu)₂]⁺-[(CH ₂tBu)Al_s]^- in 40%, 26%, and 34% yield, respectively. In ¹³C NMR calculations the important effect of spin-orbit coupling has been underlined on the chemical shifts of the carbon atoms directly linked to hafnium. Hence, a large fraction of the grafted complex is in a cationic structure, explaining why this system is active in polymerization (>10³ kg of PE/mol of Hf·h·atm) without the need of a cocatalyst, since alumina plays the dual role of solid support and Lewis acid.

Original language	English (US)
Pages (from-to)	18516-18528
Number of pages	13
Journal	JOURNAL OF PHYSICAL CHEMISTRY C
Volume	114
Issue number	43
DOIs	https://doi.org/10.1021/jp104999n
State	Published - Nov 4 2010

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
General Energy
Physical and Theoretical Chemistry
Surfaces, Coatings and Films

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@article{fd8ca38d9c6c4964b3570087e546c0cf,

title = "Alumina as a simultaneous support and CO catalyst: Cationic hafnium complex evidenced by experimental and DFT analyses",

abstract = "Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH2tBu)4, 1, on y-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl-metal bonds: Hf-CH2tBu and Al-CH 2tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [(≡AlIVO) Hf(CH2tBu)3], a neutral bis-aluminoxy [(≡Al IVO)(AlsO)Hf(CH2tBu)2], and a zwitterionic bis-aluminoxy complex [(≡AlIVO)(Al sO)Hf(CH2tBu)2]+-[(CH 2tBu)Als]- in 40%, 26%, and 34% yield, respectively. In 13C NMR calculations the important effect of spin-orbit coupling has been underlined on the chemical shifts of the carbon atoms directly linked to hafnium. Hence, a large fraction of the grafted complex is in a cationic structure, explaining why this system is active in polymerization (>103 kg of PE/mol of Hf·h·atm) without the need of a cocatalyst, since alumina plays the dual role of solid support and Lewis acid.",

author = "Marco Delgado and Santini, {Catherine C.} and Fran{\c c}oise Delbecq and Rapha{\"e}l Wischert and {Le Guennic}, Boris and G{\'e}raldine Tosin and Roger Spitz and Basset, {Jean Marie} and Philippe Sautet",

year = "2010",

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doi = "10.1021/jp104999n",

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T1 - Alumina as a simultaneous support and CO catalyst

T2 - Cationic hafnium complex evidenced by experimental and DFT analyses

AU - Delgado, Marco

AU - Santini, Catherine C.

AU - Delbecq, Françoise

AU - Wischert, Raphaël

AU - Le Guennic, Boris

AU - Tosin, Géraldine

AU - Spitz, Roger

AU - Basset, Jean Marie

AU - Sautet, Philippe

PY - 2010/11/4

Y1 - 2010/11/4

N2 - Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH2tBu)4, 1, on y-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl-metal bonds: Hf-CH2tBu and Al-CH 2tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [(≡AlIVO) Hf(CH2tBu)3], a neutral bis-aluminoxy [(≡Al IVO)(AlsO)Hf(CH2tBu)2], and a zwitterionic bis-aluminoxy complex [(≡AlIVO)(Al sO)Hf(CH2tBu)2]+-[(CH 2tBu)Als]- in 40%, 26%, and 34% yield, respectively. In 13C NMR calculations the important effect of spin-orbit coupling has been underlined on the chemical shifts of the carbon atoms directly linked to hafnium. Hence, a large fraction of the grafted complex is in a cationic structure, explaining why this system is active in polymerization (>103 kg of PE/mol of Hf·h·atm) without the need of a cocatalyst, since alumina plays the dual role of solid support and Lewis acid.

AB - Electron-poor transition metal complexes are of high interest in polymerization or oligomerization, but they require the use of a Lewis acid cocatalyst in order to reach the cationic active structure. The structure of the surface complexes obtained by grafting Hf(CH2tBu)4, 1, on y-alumina has been resolved by a combined experimental (mass balance analysis, labeling, in situ IR, NMR) and theoretical (DFT calculations) study. Thermolysis, oxidation, and hydrogenolysis reactions have unambiguously proved the presence of two kinds of neopentyl-metal bonds: Hf-CH2tBu and Al-CH 2tBu. Three coexisting surface complexes have been fully characterized and quantified: a monoaluminoxy [(≡AlIVO) Hf(CH2tBu)3], a neutral bis-aluminoxy [(≡Al IVO)(AlsO)Hf(CH2tBu)2], and a zwitterionic bis-aluminoxy complex [(≡AlIVO)(Al sO)Hf(CH2tBu)2]+-[(CH 2tBu)Als]- in 40%, 26%, and 34% yield, respectively. In 13C NMR calculations the important effect of spin-orbit coupling has been underlined on the chemical shifts of the carbon atoms directly linked to hafnium. Hence, a large fraction of the grafted complex is in a cationic structure, explaining why this system is active in polymerization (>103 kg of PE/mol of Hf·h·atm) without the need of a cocatalyst, since alumina plays the dual role of solid support and Lewis acid.

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JF - JOURNAL OF PHYSICAL CHEMISTRY C

IS - 43

ER -

Alumina as a simultaneous support and CO catalyst: Cationic hafnium complex evidenced by experimental and DFT analyses

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