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

The syntheses of two pentadentate tetrapodal phosphine (pentaPodP) ligands, P2PhPP2Ph and P2MePP2Ph, are reported, which derive from the fusion of a tripod and a trident ligand. Reaction of the ligand P2PhPP2Ph 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 P2MePP2Ph afford the mononuclear molybdenum dinitrogen complex [MoN2(P2MePP2Ph)]. 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 (ν̃NN = 1929 cm–1). The reactivity of this complex toward acids is investigated.