Organozinc Pivalate Reagents: Segregation, Solubility, Stabilization, and Structural Insights

The pivalates RZnOPivMg(OPiv)XnLiCl (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 [D-8]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)(2)Li-2(Cl)(2)(OPiv)(2)Zn].