Bis(aluminyl)magnesium: a source of nucleophilic or radical aluminium-centred reactivity

The homoleptic magnesium bis(aluminyl) compound Mg[Al(NON)]2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl -9,9-dimethylxanthene) can be accessed from K2[Al(NON)]2 and MgI2 and shown to possess a non-linear geometry (Al–Mg–Al = 164.8(1)) primarily due to the influence of dispersion interactions. This compound acts a four-electron reservoir in the reductive defluorination of SF6, and reacts thermally with polar substrates such as MeI via nucleophilic attack through aluminium, consistent with the QT-AIM charges calculated for the metal centres, and a formal description as a Al(I)–Mg(II)–Al(I) trimetallic. On the other hand, under photolytic activation, the reaction with 1,5-cyclooctadiene leads to the stereoselective generation of transannular cycloaddition products consistent with radical based chemistry, emphasizing the covalent nature of the Mg–Al bonds and a description as a Al(II)–Mg(0)–Al(II) synthon.