The syntheses of two pentadentate tetrapodal phosphine (pentaPod(P)) ligands, (P2PP2Ph)-P-Ph and (P2PP2Ph)-P-Me, are reported, which derive from the fusion of a tripod and a trident ligand. Reaction of the ligand (P2PP2Ph)-P-Ph with [MoCl3(THF)(3)] followed by an amalgam reduction under N-2 does not lead to well-defined products. The same reactions performed with the ligand (P2PP2ph)-P-Me, afford the mononuclear molybdenum dinitrogen complex [MoN2((P2PP2Ph)-P-Me)]. Because of the unprecedented topology of the pentaphosphine ligand, the Mo-P bond to the phosphine in the trans position to N-2 is significantly shortened, explaining the very strong activation of the dinitrogen ligand ((nu) over tilde (NN) = 1929 cm(-1)). The reactivity of this complex toward acids is investigated.