Well-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream?

Handle URI:
http://hdl.handle.net/10754/561067
Title:
Well-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream?
Authors:
Werghi, Baraa; Bendjeriou-Sedjerari, Anissa; Sofack-Kreutzer, Julien; Jedidi, Abdesslem ( 0000-0003-4070-3299 ) ; Abou-Hamad, Edy; Cavallo, Luigi ( 0000-0002-1398-338X ) ; Basset, Jean-Marie ( 0000-0003-3166-8882 )
Abstract:
Reaction of triisobutylaluminum with SBA15700 at room temperature occurs by two parallel pathways involving either silanol or siloxane bridges. It leads to the formation of a well-defined bipodal [(≡SiO)2Al-CH2CH(CH3)2] 1a, silicon isobutyl [≡Si-CH2CH(CH3)2] 1b and a silicon hydride [≡Si-H] 1c. Their structural identity was characterized by FT-IR and advance solid-state NMR spectroscopies (1H, 13C, 29Si, 27Al and 2D multiple quantum), elemental and gas phase analysis, and DFT calculations. The reaction involves the formation of a highly reactive monopodal intermediate: [≡SiO-Al-[CH2CH(CH3)2]2], with evolution of isobutane. This intermediate undergoes two parallel routes: Transfer of either one isobutyl fragment or of one hydride to an adjacent silicon atom. Both processes occur by opening of a strained siloxane bridge, ≡Si-O-Si≡ but with two different mechanisms, showing that the reality of “single site” catalyst may be an utopia: DFT calculations indicate that isobutyl transfer occurs via a simple metathesis between the Al-isobutyl and O-Si bonds, while hydride transfer occurs via a two steps mechanism, the first one is a ß-H elimination to Al with elimination of isobutene, whereas the second is a metathesis step between the formed Al-H bond and a O-Si bond. Thermal treatment of 1a (at 250 °C) under high vacuum (10-5 mbar) generates Al-H through a ß-H elimination of isobutyl fragment. These supported well-defined Al-H which are highly stable with time, are tetra, penta and octa coordinated as demonstrated by IR and 27Al–1H J-HMQC NMR spectroscopy. All these observations indicate that surfaces atoms around the site of grafting play a considerable role in the reactivity of a single site system.
KAUST Department:
KAUST Catalysis Center (KCC)
Citation:
Well-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream? 2015 Chem. Sci.
Journal:
Chem. Sci.
Issue Date:
17-Jul-2015
DOI:
10.1039/C5SC02276B
Type:
Article
ISSN:
2041-6520; 2041-6539
Additional Links:
http://pubs.rsc.org/en/Content/ArticleLanding/2015/SC/C5SC02276B
Appears in Collections:
Articles; KAUST Catalysis Center (KCC)

Full metadata record

DC FieldValue Language
dc.contributor.authorWerghi, Baraaen
dc.contributor.authorBendjeriou-Sedjerari, Anissaen
dc.contributor.authorSofack-Kreutzer, Julienen
dc.contributor.authorJedidi, Abdesslemen
dc.contributor.authorAbou-Hamad, Edyen
dc.contributor.authorCavallo, Luigien
dc.contributor.authorBasset, Jean-Marieen
dc.date.accessioned2015-07-27T12:23:46Zen
dc.date.available2015-07-27T12:23:46Zen
dc.date.issued2015-07-17en
dc.identifier.citationWell-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream? 2015 Chem. Sci.en
dc.identifier.issn2041-6520en
dc.identifier.issn2041-6539en
dc.identifier.doi10.1039/C5SC02276Ben
dc.identifier.urihttp://hdl.handle.net/10754/561067en
dc.description.abstractReaction of triisobutylaluminum with SBA15700 at room temperature occurs by two parallel pathways involving either silanol or siloxane bridges. It leads to the formation of a well-defined bipodal [(≡SiO)2Al-CH2CH(CH3)2] 1a, silicon isobutyl [≡Si-CH2CH(CH3)2] 1b and a silicon hydride [≡Si-H] 1c. Their structural identity was characterized by FT-IR and advance solid-state NMR spectroscopies (1H, 13C, 29Si, 27Al and 2D multiple quantum), elemental and gas phase analysis, and DFT calculations. The reaction involves the formation of a highly reactive monopodal intermediate: [≡SiO-Al-[CH2CH(CH3)2]2], with evolution of isobutane. This intermediate undergoes two parallel routes: Transfer of either one isobutyl fragment or of one hydride to an adjacent silicon atom. Both processes occur by opening of a strained siloxane bridge, ≡Si-O-Si≡ but with two different mechanisms, showing that the reality of “single site” catalyst may be an utopia: DFT calculations indicate that isobutyl transfer occurs via a simple metathesis between the Al-isobutyl and O-Si bonds, while hydride transfer occurs via a two steps mechanism, the first one is a ß-H elimination to Al with elimination of isobutene, whereas the second is a metathesis step between the formed Al-H bond and a O-Si bond. Thermal treatment of 1a (at 250 °C) under high vacuum (10-5 mbar) generates Al-H through a ß-H elimination of isobutyl fragment. These supported well-defined Al-H which are highly stable with time, are tetra, penta and octa coordinated as demonstrated by IR and 27Al–1H J-HMQC NMR spectroscopy. All these observations indicate that surfaces atoms around the site of grafting play a considerable role in the reactivity of a single site system.en
dc.relation.urlhttp://pubs.rsc.org/en/Content/ArticleLanding/2015/SC/C5SC02276Ben
dc.rightsArchived with thanks to Chem. Sci. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. http://creativecommons.org/licenses/by/3.0/en
dc.titleWell-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream?en
dc.typeArticleen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.identifier.journalChem. Sci.en
dc.eprint.versionPublisher's Version/PDFen
kaust.authorBendjeriou-Sedjerari, Anissaen
kaust.authorSofack-Kreutzer, Julienen
kaust.authorJedidi, Abdesslemen
kaust.authorAbou-Hamad, Edyen
kaust.authorCavallo, Luigien
kaust.authorBasset, Jean-Marieen
kaust.authorWerghi, Baraaen
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