Two new bulky amido ligands useful for the preparation of metal complexes and examples of their reactivity

The search for new ligands with interesting properties is a quest that can occupy much of a synthetic chemist’s time. We have recently discovered two new ligands based on an adamantyl-substituted, 2,6-iPr2-substituted phenyl (Dipp) system. In an attempt to prepare the extremely bulky amine [(ad)(2,6-iPr2C6H3)NH] (ad = adamantyl) we found instead that the adamantyl group attacks the aromatic ring in the 4-position to form a new primary amine, (4-ad-2,6-iPr2C6H2)NH2 (1) (ad-Dipp-NH2), characterized by normal techniques. Compound 1 could be converted into a Li salt by a 1:1 reaction with nBuLi, or converted into a more bulky silylamine, [(ad-Dipp)NH(SiMe3)] (3), by treatment with Me3SiCl. We have characterized the lithium salt by X-ray crystallography as the dimeric complex, [(ad-Dipp)NHLi(Et2O)]2 (2). The lithium amide can be used as a reagent towards metal halides, and we have discovered that its reaction with SnCl2 yields a compound with a tetrameric, [Sn–N]4 cubane-like cage structure. We have also demonstrated the ligand behavior of 3 by its reaction with Bu2Mg in THF to form a monomeric Mg-amide with two THF solvent molecules attached. These new ligands can provide advantages over conventional ligands in terms of improved solubility and ease of crystallization.