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

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

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    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].