Bimetallic Bis-anion Cascade Complexes of Magnesium in Nonaqueous Solution

Bimetallic magnesium(II) complexes are gaining significant interest in catalysis, yet their fundamental formation and behavior in organic media remain surprisingly unexplored relative to other divalent cations. To understand key principles of their formation, we investigate symmetric ditopic ligands bearing a phenolic backbone and characterize their ability to form dinuclear magnesium(II) cascade complexes with two bridging anions. High-fidelity production of bimetallic magnesium complexes relative to the monometallic complexes is indicative of positive cooperativity. Binding and recognition of analytes or substrates is a key characteristic of metal cascade complexes and relies on anion exchange, but this is also rarely studied with bimetallic magnesium complexes. Investigations with acetate, phosphate, and pyrophosphate reveal exchange of bridging nitrates using the bis-dipicolylamine complex. Rare seven-coordinate magnesium centers are found for the ester complex. The findings in this study provide formative steps to establish design principles for future generations of bimetallic magnesium(II) complexes.