The reaction of [(Me3Si)(2)N-Ae{mu-N(SiMe3)(2)}](2) with 2,2,5,5-tetramethyltetrahydrofuran in pentane yields the mononuclear complexes [(Me(4)thf)Ae{N(SiMe3)(2)}(2)] (Ae = Mg (1), Ca (2), Sr (3), and Ba (4)) with three-coordinate alkaline-earth metal centers. With increasing radius of the alkaline-earth metal atoms, the N-Ae-N bond angles decrease. These ether adducts significantly enhance the solubility of the bis(trimethylsilyl)amides of the alkaline-earth metals in hydrocarbon solvents. Contrary to the magnesium derivative 1, the heavier congeners dissociate into mononuclear [Ae{N(SiMe3)(2)}(2)] and free Me4THF without formation of sparingly soluble dinuclear [(Me3Si)(2)N-Ae{mu-N(SiMe3)(2)}](2).