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

Despite decades of extensive studies on the reactivity of magnesium alkyls towards O₂, the isolation and structural characterization of discrete products of these reactions still remains a challenge. Although the formation of the most frequently encountered magnesium alkoxides via unstable alkylperoxide intermediates has commonly been accepted, the latter species have been elusive for over 100 years. Probing the oxygenation of a well-defined neo-pentylmagnesium complex stabilized by a β-diketminate ligand, (dippBDI)MgCH₂CMe₃, we report on the isolation and structure characterization of both a dimeric magnesium alkoxide [(dippBDI)Mg(µ-OCH₂CMe₃)]2 and the first example of monomeric magnesium alkylperoxide [(dippBDI)Mg(thf)OOCH₂CMe₃] (dippBDI = [(ArNCMe)₂CH]- and Ar = C₆H₃iPr₂-2,6). The formation of monomeric magnesium alkylperoxide demonstrate a crucial role of an additional Lewis base for stabilizing the most elusive oxygenation products likely due to increasing of the electron density on the metal centre. Moreover, the ¹H NMR studies at - 80 °C revealed that the dissociation of a coordinated Lewis base from the solvated complex (dippBDI)Mg(L)CH₂CMe₃ (where L = thf or 4-methylpyridine) is likely not required prior to the effective attack of an O₂ molecule on the metal centre and the four-coordinate alkylmagnesium complex reacts smoothly with O₂ under these conditions. The results can be expected to aid future engineering of various organomagnesium/O₂-based reaction systems.