Mo-0 dinitrogen complexes bearing electron-rich mono- and bidentate phosphines can be synthesized in good yields from inexpensive and readily accessible MoCl5 via a one-step mild reduction with Mg metal. trans-[(N-2)(2)Mo(PMePh2)(PPh(CH2CH2PPh2)2)] can also be obtained via this strategy. However, in the presence of tri- and tetradentate ligands that are sterically restrictive, the analogous reduction leads to either (eta(6)-arene) formation or [Mo(multidentate phosphine)(m)](n) oligomer complexes that have no dinitrogen ligands. One such eta(6)-arene complex, where the Mo-0 center is ligated by 1,1,1-tris(diphenylphosphinomethyl)ethane, was isolated and characterized via X-ray crystallography.