Organozinc pivalate reagents : segregation, solubility, stabilisation and structural insights

Hernán-Gómez, Alberto and Herd, Emma and Hevia, Eva and Kennedy, Alan R. and Knochel, Paul and Koszinowski, Konrad and Manolikakes, Sophia M. and Mulvey, Robert E. and Schnegelsberg, Christoph (2014) Organozinc pivalate reagents : segregation, solubility, stabilisation and structural insights. Angewandte Chemie International Edition, 53 (10). 2706–2710. ISSN 1433-7851

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    Abstract

    The pivalates RZnOPiv⋅Mg(OPiv)X⋅n LiCl (OPiv=pivalate; R=aryl; X=Cl, Br, I) stand out amongst salt-supported organometallic reagents, because apart from their effectiveness in Negishi cross-coupling reactions, they show more resistance to attack by moist air than conventional organometallic compounds. Herein a combination of synthesis, coupling applications, X-ray crystallographic studies, NMR (including DOSY) studies, and ESI mass spectrometric studies provide details of these pivalate reagents in their own right. A p-tolyl case system shows that in [D8]THF solution these reagents exist as separated Me(p-C6H4)ZnCl and Mg(OPiv)2 species. Air exposure tests and X-ray crystallographic studies indicate that Mg(OPiv)2 enhances the air stability of aryl zinc species by sequestering H2O contaminants. Coupling reactions of Me(p-C6H4)ZnX (where X=different salts) with 4-bromoanisole highlight the importance of the presence of Mg(OPiv)2. Insight into the role of LiCl in these multicomponent mixtures is provided by the molecular structure of [(THF)2Li2(Cl)2(OPiv)2Zn].