New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones : structural authentication of a beta-hydride elimination product containing a tetranuclear zinc chain

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Hevia, Eva and Kennedy, Alan R. and Klett, Jan and Livingstone, Zoe and McCall, Matthew D. (2010) New insights into addition reactions of dialkylzinc reagents to trifluoromethyl ketones : structural authentication of a beta-hydride elimination product containing a tetranuclear zinc chain. Dalton Transactions, 39 (2). pp. 520-526. ISSN 1472-7773 (https://doi.org/10.1039/b911818g)

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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, Bu-t, CH2SiMe3; TMEDA = N, N, N', N'-tetramethylethylenediamine) monitored by H-1 and F-19 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 = Bu-t, the reduction product [(TMEDA)Zn(Bu-t){OC(CF3)(H)Ph}] is obtained as a result of beta-hydride elimination from one of the tBu groups of the organometallic reagent. H-1 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 beta 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 [(Bu-t)(2)Zn-4{OC(CF3)(H)Ph}(6)] (5) resulting from the reduction of 1 when reacted with (Bu2Zn)-Bu-t, which displays a rare Zn...Zn...Zn...Zn linear chain arrangement for a zinc alkyl(alkoxide).

ORCID iDs

Hevia, Eva ORCID logoORCID: https://orcid.org/0000-0002-3998-7506, Kennedy, Alan R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015, Klett, Jan, Livingstone, Zoe and McCall, Matthew D.;
CORE (COnnecting REpositories)