Heterobimetallic alkaline earth metal-metal bonding

Low-oxidation-state complexes of type (BDI)Mg-Mg(BDI) (BDI, beta-diketiminate) show broad reactivity, finding application as soluble, universal reducing agents, enriching the field of early main group metal chemistry. Attempts to isolate similar, but considerably more reactive, Ca-Ca bound complexes have so far failed. As the metal-metal bond strength descending group 2 rapidly decreases, BDI complexes of the heavier AeI (alkaline earth) ions (Ae = Ca, Sr, Ba) probably exist as (BDI)Ae center dot radicals of untamed reactivity. Here we describe a facile method to prepare stable but highly reactive complexes with heterobimetallic Mg-Ae bonds. Mixing [(BDI)Mg ˉNa+]2 and [Ae(NR2)2]2 dimers led to anion-cation exchange and exclusive formation of mixed species: (BDI)Mg ˉNa+/Ae(NR2)2 (Ae = Ca, Sr, Ba; R = SiMe3). Crystal structures feature examples of Mg-Ca and Mg-Sr bonding with formal oxidation states of Mg0-AeII. Best described as polarized Mg delta ˉ-Ae delta+ bonds, these complexes show potential as alkane-soluble reductants for bond activation, which readily react with benzene by C-H bond cleavage and are oxidized to discrete complexes with N2O. Cation-anion exchange between dimers to prepare mixed aggregates with Mg-Ae (alkaline earth) bonding (Ae = Mg, Ca, Sr, Ba) is reported. Considerable electron transfer from the (BDI)Mg ˉ anion (BDI, beta-diketiminate) to Ae and Na atoms is observed, and the reactivity of these electron-rich complexes with Na-Mg-Ae bonding is discussed.