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Issue 2, 2010
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New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones: Structural authentication of a β-hydride elimination product containing a tetranuclear zinc chain

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Abstract

A systematic study of the stoichiometric alkylation reactions of 2,2,2-trifluoroacetophenone 1 with [ZnR2(TMEDA)] (R= Me, Et, tBu, CH2SiMe3; TMEDA= N,N,N,N′-tetramethylethylenediamine) monitored by 1H and 19F NMR spectroscopy is presented. For R = Me, Et the alkylation products alkyl(alkoxides) [(TMEDA)Zn(R){OC(CF3)(R)Ph}] (R = Me, 2: Et, 3) are obtained as the single products of the reaction. When the steric bulk of the dialkylzinc reagent is increased the alkylation reaction is inhibited. Thus, for R = tBu, the reduction product [(TMEDA)Zn(tBu){OC(CF3)(H)Ph}] is obtained as a result of β-hydride elimination from one of the tBu groups of the organometallic reagent. 1H NMR spectroscopic monitoring of the reaction allowed the detection of isobutene as a side product of this reduction process. For the highly sterically demanding group R = CH2SiMe3 which lacks hydrogen atoms at the β position, no reaction is observed even under refluxing conditions. Two important intermediates from these reactions have been structurally elucidated: [(TMEDA)Zn(Me){OC(CF3)(Me)Ph}] (2) which could be involved in the previously reported alkylation reaction of trifluoromethyl ketones by ZnR2 catalysed by TMEDA and unprecedented tetranuclear [(tBu)2Zn4{OC(CF3)(H)Ph}6] (5) resulting from the reduction of 1 when reacted with tBu2Zn, which displays a rare Zn⋯Zn⋯Zn⋯Zn linear chain arrangement for a zinc alkyl(alkoxide).

Graphical abstract: New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones: Structural authentication of a β-hydride elimination product containing a tetranuclear zinc chain

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Publication details

The article was received on 17 Jun 2009, accepted on 18 Aug 2009 and first published on 10 Sep 2009


Article type: Paper
DOI: 10.1039/B911818G
Citation: Dalton Trans., 2010,39, 520-526
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    New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones: Structural authentication of a β-hydride elimination product containing a tetranuclear zinc chain

    E. Hevia, A. R. Kennedy, J. Klett, Z. Livingstone and M. D. McCall, Dalton Trans., 2010, 39, 520
    DOI: 10.1039/B911818G

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