Suppressing Cis/Trans ‘Ring‐Flipping’ in Organoaluminium(III)‐2‐Pyridyl Dimers–Design Strategies Towards Lewis Acid Catalysts for Alkene Oligomerisation

Author:

Choudhury Dipanjana1ORCID,Lam Ching Ching1ORCID,Farag Nadia L.1ORCID,Slaughter Jonathan12ORCID,Bond Andrew D.1ORCID,Goodman Jonathan M.1ORCID,Wright Dominic S.1ORCID

Affiliation:

1. Yusuf Hamied Department of Chemistry University of Cambridge Lensfield Road Cambridge CB2 1EW

2. The Faraday Institution Quad One Harwell Science and Innovation Campus Didcot OX11 0RA United Kingdom

Abstract

AbstractOwing to its high natural abundance compared to the commonly used transition (precious) metals, as well as its high Lewis acidity and ability to change oxidation state, aluminium has recently been explored as the basis for a range of single‐site catalysts. This paper aims to establish the ground rules for the development of a new type of cationic alkene oligomerisation catalyst containing two Al(III) ions, with the potential to act co‐operatively in stereoselective assembly. Five new dimers of the type [R2Al(2‐py′)]2 (R=Me, iBu; py′=substituted pyridyl group) with different substituents on the Al atoms and pyridyl rings have been synthesised. The formation of the undesired cis isomers can be suppressed by the presence of substituents on the 6‐position of the pyridyl ring due to steric congestion, with DFT calculations showing that the selection of the trans isomer is thermodynamically controlled. Calculations show that demethylation of the dimers [Me2Al(2‐py′)]2 with Ph3C+ to the cations [{MeAl(2‐py’)}2(μ‐Me)]+ is highly favourable and that the desired trans disposition of the 2‐pyridyl ring units is influenced by steric effects. Preliminary experimental studies confirm that demethylation of [Me2Al(6‐MeO‐2‐py)]2 can be achieved using [Ph3C][B(C6F5)4].

Funder

Trinity College, University of Cambridge

Engineering and Physical Sciences Research Council

Faraday Institution

Shell

Publisher

Wiley

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