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Issue 8, 2019
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Reversible alkene binding and allylic C–H activation with an aluminium(i) complex

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Abstract

The monomeric molecular aluminium(I) complex 1 [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products. Remarkably all these reactions are reversible under mild conditions (298–353 K) with alkene binding being disfavoured at higher temperatures due to the positive reaction entropy. Van't Hoff analyses have allowed quantification of the binding events with Image ID:c8sc04865g-t1.gif. Calculations and single crystal X-ray diffraction studies are consistent with the alkene bound species being metallocyclopropane complexes. Alkene binding involves a reversible redox process with changes from the +1 to +3 aluminium oxidation state. Under more forcing conditions the metallocyclopropane complexes undergo non-reversible allylic C–H bond activation to generate aluminium(III) allyl hydride complexes. This represents a rare example of redox-based main group reactivity in which reversible substrate binding is followed by a further productive bond breaking event. Analysis of the mechanism reveals a reaction network in which alkene dissociation and reformation of 1 is required for allylic C–H activation, a realisation that has important implications for the long-term goal of developing redox-based catalytic cycles with main group compounds.

Graphical abstract: Reversible alkene binding and allylic C–H activation with an aluminium(i) complex

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Publication details

The article was received on 31 Oct 2018, accepted on 04 Jan 2019 and first published on 08 Jan 2019


Article type: Edge Article
DOI: 10.1039/C8SC04865G
Chem. Sci., 2019,10, 2452-2458
  • Open access: Creative Commons BY license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    Reversible alkene binding and allylic C–H activation with an aluminium(I) complex

    C. Bakewell, A. J. P. White and M. R. Crimmin, Chem. Sci., 2019, 10, 2452
    DOI: 10.1039/C8SC04865G

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