Oxygenation of a Me₂Zn/α‐Diimine System: A Unique Zinc Methylperoxide Cluster and Evidence for Its Sequential Decomposition Pathways

Abstract

O what a reaction: The oxygenation of Me2Zn⋅tBu‐DAB (tBu‐DAB=1,4‐di‐tert‐butyl‐1,4‐diazabutadiene) affords the unprecedented oxo(methylperoxide) cubane 1, the corresponding double cubic oxo(methoxide) 2, and the CC coupled dinuclear methoxide [(MeZn)2(tBu‐DAB‐DAB(H)‐tBu)(μ‐OMe)], the formation of which involves initial ZnOOMe bond homolysis.

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

“…As already noted, the widely accepted mechanism implies that the formation of an alkoxide species is a consequence of a metathesis reaction between the resulting zinc alkylperoxide and the parent alkylzinc compound (Scheme a; metathesis) . Conversely, our results on the oxygenation of 1 and 2 at low temperature, along with earlier reported precedents concerning the oxygenation chemistry of zinc,, aluminum, and particularly magnesium alkyls, stand in clear contradiction to this widely accepted metathesis process. The formation of zinc alkoxides can be rationalized in terms of an intramolecular transformation of zinc alkylperoxides (Scheme ; the proposed η 2 ‐binding mode of alkylperoxide ligand has previously been observed for aluminum and magnesium alkylperoxide complexes).…”

“…During the last decade, our group's studies have provided a fresh perspective on such oxygenation processes, and have indicated that, despite the involvement of radical species, a radical‐chain process alone cannot fully explain all of the experimental observations . For example, we have convincingly demonstrated the essential role of both the coordination state of the organometallic species (M=Al, Zn,‐ or Mg) and the geometric requirements of an O 2 molecule approaching the metal center in the case of rationally designed aluminum alkyls . In the latter case, the combined structural and chemical patterns provided compelling experimental evidence that attack of O 2 on the metal center from a desired direction is the key feature in O 2 activation by tetrahedral organoaluminum complexes, prior to insertion of the dioxygen molecule into the Al−C bond .…”

“…Reactivity of the Lewis acid–base adduct [L][ZnEt(py‐Me)] 2 towards O 2 : Our previous studies on the oxygenation of dialkylzinc complexes bearing donor ligands demonstrated that access of an O 2 molecule to the three‐coordinate zinc center is a crucial factor –. Conversely, to the best our knowledge, the reactivity towards O 2 of monoalkylzinc complexes bearing N , N ‐ligands in the presence of a Lewis base has not been studied.…”

“…The same issue has not yet been convincingly resolved for alkylzinc and alkylmagnesium complexes. So far, the data only indicate that four‐coordinate zinc alkyl species do not display reactivity towards dioxygen, in contrast to the three‐coordinate species, which react swiftly –…”

De Novo Design of Tetranuclear Transition Metal Clusters Stabilized by Hydrogen-Bonded Networks in Helical Bundles

“…Other tetranuclear Zn 2+ sites appeared to be embedded in larger complexes that contain up to more than eight Zn 2+ ions. 75,76 …”