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    Demonstration of Promoted Zinc Schlenk Equilibria, their Equilibrium Values and Derived Reactivity

    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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    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:
    Depositing User: Dr John Stephens
    Date Deposited: 10 Jan 2017 15:07
    Journal or Publication Title: Chemistry : a European Journal
    Publisher: Wiley
    Refereed: Yes
    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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