Development of zinc alkyl/air systems as radical initiators for organic reactions

Abstract

A novel organozinc initiator with a clear mechanistic signature for organic radical reactions has been developed.

Exploration of Dimethylzinc‐Mediated Radical Reactions

“…This regioselectivity is in good agreement with the reported relative rate of hydrogen abstraction at the 2‐ and 4‐positions by tert ‐butoxyl radical (3:1 at 60°C) . This indicates that O‐centered radical species rather than the methyl radical mainly abstract the hydrogen atom …”

Unprecedented Variety of Outcomes in the Oxygenation of Dinuclear Alkylzinc Derivatives of an N,N‐Coupled Bis(β‐diketimine)

“…[16] The angle between the b-diketiminate units (À104.9(6)8)i sn early equal to that found in 2 (107.18). The Zn-N py-Me bond lengths are 2.184(5) and 2.172 (5) .T he coordination of py-Me results in slight elongation of the ZnÀCb onds (average 1.997 ,a so pposedt o 1.959 in 2 [15] ).…”

“…Reactivityo fm ethylzinc complex1towards O 2 :Asolutiono f 1 in toluene showedn os ign of oxidation at À20 8Cd uring 1h under dryO 2 atmosphere.H owever,w hen the solution was agitated for 30 min at ambient temperature, ac olor change from yellow to orange was observed. Upon removal of the O 2 followed by concentration of the reaction mixture and storage at À20 8C, crystals of the partially oxygenated tetranuclear methyl(methoxy)zinc complex, (5), were isolated in moderate yield (isolated yields up to 46 %) (Scheme 2, Figure 2a). Although the reactionw as performed multiple times, 5 was the only isolable product.…”

“…Thus, despite extensive research in the field, uncertainties concerning the nature of the initial products and the metal-based final products have remained, and the exact mechanism of the oxygenation of organometallics with non-redox-active metal centers has not been fully elucidatedf or decades. However,d ue to ac onsiderable increase in practical applications of metal alkyl/O 2 reaction systems in chemistry and materials science, for example, in organic radical reactions, [5] epoxidationso fe nones [6,7] and allylic olefins, [8] and the preparation of ZnO nanocrystals, [9] ad etailedk nowledge of the O 2 activation mechanism by this family of organometallics and furtherp ossible reactionp athways is undoubtedly needed. During the last decade, our group's studies have provided af resh perspective on such oxygenationp rocesses, and have indicatedt hat, despite the involvement of radical species, ar adical-chainp rocess alone cannot fully explain all of the experimental observations.…”

Reaching Milestones in the Oxygenation Chemistry of Magnesium Alkyls: towards Intimate States of O2 Activation and the First Monomeric Well‐Defined Magnesium Alkylperoxide

“…Moreover, we have also emphasized the essential role of the coordination state of the oxygenated organoaluminum and organozinc compounds, as well as the geometric requirements of an O 2 molecule approaching the metal centre . Apart from the fundamental aspects, these systematic studies have advanced rational design of metal alkyl/air systems as radical initiators for organic reactions, stoichiometric and catalytic asymmetric epoxidation of enones and pave the way to well‐defined metal alkoxides (not accessible through the classical alcoholysis path) as potential initiators of cyclic esters polymerization as well as to a new approach for the preparation of semiconductor zinc oxide quantum dots based on organozinc/air systems …”