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

Baraa Werghi, Anissa Bendjeriou-Sedjerari, Julien Sofack-Kreutzer, Abdesslem Jedidi, Edy Abou-Hamad, Luigi Cavallo, Jean-Marie Basset

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

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.
Original languageEnglish (US)
Pages (from-to)5456-5465
Number of pages10
JournalChem. Sci.
Volume6
Issue number10
DOIs
StatePublished - 2015

Fingerprint Dive into the research topics of 'Well-Defined Silica Supported Aluminum Hydride: Another Step Towards the Utopian Single Site Dream?'. Together they form a unique fingerprint.

Cite this