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

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].

Association and Dissociation of Grignard Reagents RMgCl and Their Turbo Variant RMgCl⋅LiCl

“…At c =1.0 m , the highest concentration that could be probed, the diffusion coefficient slightly increased. This behavior could indicate the partial formation of a higher aggregate interrelated to the [RMgCl(THF) 2 ] species via a fast equilibrium; the validity of the ECC DOSY method has, however, not been rigorously demonstrated for highly concentrated sample solutions …”

Probing the Role of π Interactions in the Reactivity of Oxygen Species: A Case of Ethylzinc Aryloxides with Different Dispositions of Aromatic Rings toward the Metal Center

“…DOSY measurements were performed in dry and degassed [D 8 ]toluene or [D 8 ]THF as we exploited the physical properties of the diluted solution, namely, density and viscosity, as these properties deviate only slightly from those the pure solvents. [24] A pulsed field-gradient double-stimulated echo-convection-compensated (PFGSTE) sequence with a total of 15 diffusion encoding gradients (from 3 to 45 G cm À1 , sine-shaped equal steps in gradient squared) was used and the total width of the gradient pulse was optimized to achieve an attenuation of about 90 % of the initial intensity of the signals. Overall, the important acquisition parameters were: total length of the encoding pulses gradient = 2 ms, diffusion delay = 50 ms, gradient recovery delay = 1 ms, relaxation delay = 2 s. Steady-state scans (16) were performed before the acquisition of the data.…”

Herstellung von festen, substituierten Allylzinkreagentien und deren Reaktionen mit Elektrophilen

“…[9] Hier beschreiben wir die Synthese der ersten festen Allylzinkreagentien des Ty ps 1 durch die Insertion von Zinkpulver [10] in der Gegenwart von LiCl [11] und Magnesiumpivalat (Mg(OPiv) 2 ;O Piv = OCOtBu) in verschiedene allylische Bromide oder Chloride des Ty ps 2.N ach Entfernen des Lçsungsmittels wurden die festen, allylischen Reagentien als weiße oder gelbe Pulver erhalten. [13] Die Rolle des LiCl ist die Aktivierung des Zinkpulvers,w ohingegen gefunden wurde,d ass Mg(OPiv) 2 essenziell für die Langzeitstabilität der festen allylischen Reagentien ist. Wichtige funktionelle Gruppen, wie ein Ester oder ein Nitril, werden in diesen Reagentien toleriert (siehe 1e-h).…”

“…Die Gegenwart von LiCl und Mg(OPiv) 2 ist essenziell für die Herstellung dieser allylischen Zinkreagentien. [13] Die Rolle des LiCl ist die Aktivierung des Zinkpulvers,w ohingegen gefunden wurde,d ass Mg(OPiv) 2 essenziell für die Langzeitstabilität der festen allylischen Reagentien ist. [14] Zunächst bromid Kreuzkupplungen mit verschiedenen ungesättigten Bromiden in der Gegenwart eines Pd-Präkatalysators und eines sterisch gehinderten Phosphinliganden (CPhos) eingeht.…”