With [Mo(N 2)(P 2 Me PP 2 Ph Scheme1.Molybdenum-based models ystems for synthetic nitrogen fixation.

The syntheses of two pentadentate tetrapodal phosphine (pentaPod(P)) ligands, P2(Ph)PP2(Ph) and P2(Me)PP2(Ph), are reported, which derive from the fusion of a tripod and a trident ligand. Reaction of the ligand P2(Ph)PP2(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(Me)PP2(Ph) afford the mononuclear molybdenum dinitrogen complex [MoN2(P2(Me)PP2(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 (ν̃NN = 1929 cm(-1)). The reactivity of this complex toward acids is investigated.

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What is the most significant result of this study? …that ac areful ligand design allows us to create molecular complexes that can both activate N 2 and form robust catalysts that are not prone to ligand loss. The molybdenum dinitrogen complex [Mo(N 2)(P 2 Me PP 2 Ph