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

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Title: Reversible alkene binding and allylic C–H activation with an aluminium(i) complex
Authors: Bakewell, C
White, AJP
Crimmin, MR
Item Type: Journal Article
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.
Issue Date: 28-Feb-2019
Date of Acceptance: 4-Jan-2019
URI: http://hdl.handle.net/10044/1/66729
DOI: https://dx.doi.org/10.1039/c8sc04865g
ISSN: 2041-6520
Publisher: Royal Society of Chemistry (RSC)
Journal / Book Title: Chemical Science
Copyright Statement: © 2019 The Author(s). This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/).
Sponsor/Funder: The Leverhulme Trust
Commission of the European Communities
Funder's Grant Number: RPG-2015-248
677367
Publication Status: Published online
Online Publication Date: 2019-01-08
Appears in Collections:Chemistry



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