Bis(2-Adamantyl)Magnesium: Synthesis, Structure, and Applications of a Versatile and Shelf-Stable 2-Adamantyl Anion...

The adamantyl substituent is used extensively in pharmaceuticals and materials, as well as in phosphine ligands and metal complexes for catalysis. The 1-adamantyl group (1-Ad), where adamantyl is bound at the bridgehead position, is most widely used, in part due to the ease by which the 1-adamantyl cation is formed. The 2-adamantyl group (2-Ad), where the bridge position is substituted, is underutilized and so are anionic adamantyl precursors. To provide better building blocks for adamantyl chemistry, we are developing potent and stable 2-adamantyl anions. While arguably the most powerful 2-adamantyl anion is 2-adamantyl lithium, its synthesis is poorly reproducible, and the compound is so unstable that it is poorly characterized and can be used in situ only. The last several years have seen, in increasing order of carbanionic character, reproducible syntheses of (2-Ad)ZnBr, (2-Ad)₂ Zn, and (2-Ad)MgBr, all of which are shelf-stable. We now report the synthesis and application of (2-Ad)₂Mg as a nucleophile for organic and organometallic chemistries. It is, in practical use (as tested in transmetallation onto molybdenum) a more powerful transmetallating agent than (2-Ad)MgBr and is shelf-stable for months in solution or in crystalline form as the thf/dioxane adduct. Crystal structures are provided for (2-Ad)MgBr as its TMEDA adduct, (2-Ad)₂Mg as a dimetallic solvate (terminal thf, bridging dioxane), the product of transmetallation onto a dimetallic molybdenum complex, and several organic products resulting from 2-Ad anion transfer onto aldehyde carbonyl groups.