Reactions of Hydrazido(2-) Complexes Derived from Molybdenum and Tungsten Dinitrogen Complexes

Since the discovery of the first dinitrogen complex of molybdenum, trans-[Mo(N2)2(dpe)2] (dpe = Ph2PCH2CH2PPh2)1, many dinitrogen complexes of molybdenum and tungsten have been prepared and their chemical properties have been extensively studied for possible relevance to nitrogen fixation as well as to open a new chemistry of dinitrogen.2 Until now, many hydrazido(2-) complexes have been isolated as an intermediate stage in the reduction of dinitrogen. The hydrazido(2−) complexes, [MF(NNH2)(dpe)2][BF4] (M = Mo or W), are readily obtained by the reaction of trans- [M[N2)2(dpe)2] with fluoroboric acid.3,4 On the other hand, treatment of [M(N2)2(PMe2 Ph)4] (M = Mo or W) with aqueous HX (X = Cl, Br, or I) in methanol affords a series of the hydrazido(2-) complexes [MX2(NNH2)(PMe2Ph)3] in good yields. The X-ray structure of the former hydrazido(2−) complex (M = Mo) shows that the Mo-N-N linkage is essentially linear. The N-N bond distance indicates a bond order greater than unity while the Mo-N bond distance is consistent with considerable multiple bonding between the metal and nitrogen.4 This result is interpreted in terms of a combination of two resonance structures (i) and (ii).