Blake, Alexander J. and Shannon, Jonathan and Stephens, John C. and Woodward, Simon (2007) Demonstration of Promoted Zinc Schlenk Equilibria, their Equilibrium Values and Derived Reactivity. Chemistry : a European Journal, 13 (9). pp. 2462-2472. ISSN 0947-6539

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Abstract

The presence of promoted Schlenk equilibria for organozinc halide species has been explicitly demonstrated by 13C NMR studies. Thus, addition of methylaluminoxane (MeAlO)n, MAO, to RZnX (R=Et, Bn, ArCH2, (CH2)3CO2Et; X=Cl, Br) leads to the formation of ZnR2 and ZnX2⋅MAO. For EtZnCl, equilibration of ZnEt2 and ZnX2⋅MAO is rapid at −35 °C; a K value of 0.19 M−1 indicates the equilibrium favours ZnEt2 (0.75–3.0 equiv MAO). Use of RZnX/MAO mixtures allows copper-catalysed 1,4-addition to 2-cyclohexenone to be achieved, but a competing cascade reaction (two subsequent Michael additions and an intramolecular aldol reaction) leads to novel tetracyclic by-products (characterised crystallographically in one case). Activation of EtZnCl is also achieved by ZnMe2 addition and the presence of intermediate EtZnMe was observed by 13C NMR spectroscopy (at equilibrium, K≈1). Asymmetric conjugate addition in this system can be realised (up to 92 % ee for additions to 2-cyclohexenone).

Item Type:	Article
Additional Information:	This work was supported by the European Union Framework 6 Programme (Project: FP6-505267-1; LIGBANK, J.C.S.) and we thank the EPSRC-funded synchrotron crystallography service and its director Professor W. Clegg for collection of single-crystal diffraction data at Daresbury SRS Station 9.8. J.S. thanks the EPSRC for its contribution to a studentship. We acknowledge Dr. Chris Frost (University of Bath) for useful discussions.
Keywords:	aluminum; diorganozinc; organozinc halide; Schlenk equilibria; structure elucidation; zinc;
Academic Unit:	Faculty of Science and Engineering > Chemistry
Item ID:	7706
Identification Number:	https://doi.org/10.1002/chem.200601739
Depositing User:	Dr John Stephens
Date Deposited:	10 Jan 2017 15:07
Journal or Publication Title:	Chemistry : a European Journal
Publisher:	Wiley
Refereed:	Yes
URI:	http://onlinelibrary.wiley.com
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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