This study details the synthesis and characterization of an unprecedented two-coordinate, high-spin manganese(0) complex that incorporates an unsupported Mn-Mg bond, viz. (LMnMg)-Mn-dagger((Mes)Nacnac) (L-dagger = -N(Ar-dagger)(SiPr3i), Ar-dagger = C6H2{C(H)Ph-2}(2)Pr-i-2,6,4; (Mes)Nacnac = [(MesNCMe)(2)CH](-); Mes = mesityl). This compound has been utilized as an "inorganic Grignard reagent" in the preparation of the first two-coordinate manganese(I) dimer, (LMnMnL)-Mn-dagger* (L* = -N(Ar*)(SiMe3), Ar* = C6H2{C(H)Ph-2}(2)Me-2,6,4), and the related mixed valence, bis(amido)-hetereobimetallic complex, Mn-II(mu-L-dagger)(mu-L*)Cr-0. It is also shown to act as a two-electron reducing agent in reactions with unsaturated substrates.