Molybdenum(0) Dinitrogen Complexes Supported by Pentadentate Tetrapodal Phosphine Ligands: Structure, Synthesis, and Reactivity toward Acids

The syntheses of two pentadentate tetrapodal phosphine (pentaPod^P) ligands, P₂^PhPP₂^Ph and P₂^MePP₂^Ph, are reported, which derive from the fusion of a tripod and a trident ligand. Reaction of the ligand P₂^PhPP₂^Ph with [MoCl₃(THF)₃] followed by an amalgam reduction under N₂ does not lead to well-defined products. The same reactions performed with the ligand P₂^MePP₂^Ph afford the mononuclear molybdenum dinitrogen complex [MoN₂(P₂^MePP₂^Ph)]. Because of the unprecedented topology of the pentaphosphine ligand, the Mo–P bond to the phosphine in the trans position to N₂ is significantly shortened, explaining the very strong activation of the dinitrogen ligand (ν̃_NN = 1929 cm^–1). The reactivity of this complex toward acids is investigated.