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 through unstable alkylperoxide intermediates has commonly been accepted, the latter species have been elusive for over 100 years. Probing the oxygenation of a seemingly simple well-defined neo-pentylmagnesium complex stabilized by a β-diketiminate ligand, (dipp BDI)MgCH2 CMe3 , we report on the isolation and structure characterization of both a dimeric magnesium alkoxide [(dipp BDI)Mg(μ-OCH2 CMe3 )]2 and the first example of monomeric magnesium alkylperoxide [(dipp BDI)Mg(thf)OOCH2 CMe3 ] (dipp BDI=[(ArNCMe)2 CH]- and Ar=C6 H3 iPr2 -2,6). The formation of monomeric magnesium alkylperoxide demonstrates 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 1 H NMR studies at -80 °C revealed that the dissociation of a coordinated Lewis base from the solvated complex (dipp BDI)Mg(L)CH2 CMe3 (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.