Two Mg-Mg-bonded compounds were synthesized by using the ligands N,N'-bis(dipp)-phenanthrene-9,10-diimine (L2) and N,N'-bis(dipp)-o-phenylenediamine (H2L3; dipp = 2,6-diisopropylphenyl). These new Mg(i) species were characterized by X-ray diffraction, NMR, UV-Vis and fluorescence spectroscopy, and DFT computations. Their reactions with unsaturated organic molecules were examined.