Metalation of 2,4,6-trimethylacetophenone using organozinc reagents: the role of the base in determining composition and structure of the developing enolate

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Armstrong, D.R. and Drummond, A.M. and Balloch, L. and Graham, D.V. and Hevia, E. and Kennedy, A.R. (2008) Metalation of 2,4,6-trimethylacetophenone using organozinc reagents: the role of the base in determining composition and structure of the developing enolate. Organometallics, 27 (22). pp. 5860-5866. ISSN 0276-7333 (http://dx.doi.org/10.1021/om800658s)

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Abstract

The new mixed lithium−zinc enolate compounds [(TMEDA)2Li2Zn{OC(CH2)Mes}4] (2) and [{TMP(H)}2Li2Zn{OC(CH2)Mes}4] (3) were prepared by reaction of the sterically demanding ketone 2,4,6-trimethylacetophenone (1) with the all-amido homoleptic zincate [LiZn(TMP)3] (TMP = 2,2,6,6-tetramethylpiperidide). X-ray crystallographic studies revealed that these compounds adopt a trinuclear Li···Zn···Li chain arrangement with enolate O bridges. In contrast, the metalation of 1 with heteroleptic [(TMEDA)LiZn(TMP)Me2] afforded the dimeric lithium enolate [(TMEDA)2Li2{OC(CH2)Mes}2] (4) as a crystalline solid, which has been characterized in the solid state by X-ray crystallography, and Me2Zn·TMEDA and TMP(H) as coproducts, showing that the dimethylamido zincate behaves as an amide base. The homoleptic zinc enolate [(TMEDA)Zn{OC(CH2)Mes}2] (5) was obtained by reaction of 1 with the zinc amide Zn(TMP)2, and its structure was determined by X-ray crystallography. 5 adopts a rarely observed monomeric arrangement where the two enolate groups bind terminally to the zinc. New enolates 2−5 have also been characterized by 1H, 13C, and 7Li NMR spectroscopy in C6D6 solution. DFT studies of the metalation of 1 by Zn(TMP)2 and Et2Zn revealed that the former amide has a much greater kinetic basicity than the latter alkyl reagent. Copyright © 2010 American Chemical Society

ORCID iDs

Armstrong, D.R., Drummond, A.M., Balloch, L., Graham, D.V., Hevia, E. ORCID logoORCID: https://orcid.org/0000-0002-3998-7506 and Kennedy, A.R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015;
  • Item type:Article
    ID code:17015
    Dates:
    Date
    Event
    24 November 2008
    Published
    Notes:http://suprimo.lib.strath.ac.uk/primo_library/libweb/action/search.do?ct=facet&fctN=facet_fmt&fctV=include+only+journals+or+serials&frbg=&dum=true&vid=SUVU01&vl(54032236UI0)=lsr02&vl(96071691UI1)=all_items&srt=rank&indx=1&dstmp=1270123144070&tab=local&ct=search&scp.scps=scope%3A(SU)&vl(freeText0)=Organometallics&fn=search&mode=Basic&dscnt=0 ; Abstract taken from http://pubs.acs.org/doi/abs/10.1021/om800658s
    Subjects:Science > Science (General)
    Science > Chemistry
    Science > Chemistry > Physical and theoretical chemistry
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Strathprints Administrator
    Date deposited:05 Apr 2010 09:30
    Last modified:11 Nov 2024 09:23
    URI:https://strathprints.strath.ac.uk/id/eprint/17015
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