Remarkably volatile magnesium complexes have been prepared with the modified borohydride ligand N,N-dimethylaminodiboranate, H3BNMe2BH3-. The homoleptic complex Mg(H3BNMe2BH3)(2), its monoadducts with tetrahydrofuran and 1,2-dimethoxyethane, and the mixed ligand complex (C5Me5)Mg(H3BNMe2BH3)(thf) have been prepared. The homoleptic complex Mg(H3BNMe2BH3)(2) has a vapor pressure of 800 mTorr at 25 degrees C, which makes it the most volatile magnesium complex known. Crystal structures and NMR data are reported for all complexes. The compounds are potentially useful as chemical vapor deposition precursors to MgB2 and MgO, and as hydrogen storage materials.