Dinitrogen hydrazido complexes

Combining the electroreduction of the hydrazido Mo complex (377) and the regeneration of the dinitrogen Mo complex (374) opens up the possibility of an electrochemical... 

Hydrazido(2 —) complexes are most prevalent within group VI although there are to date no reported hydrazido complexes of chromium. Representative examples of known structure are shown in Table 16. Sulfur coligands predominate reflecting the metal-sulfur coordination in nitrogenase and the participation of hydrazide ligands in dinitrogen chemistry. 

X-ray structures of Mo and W dinitrogen, hydrazido(2-), and hydrazidium complexes with dppe and depe co-ligands exist. Figure 1 gives... 

Returning now to the importance of the hydrazido ligand as an intermediate in dinitrogen reduction, it is noted that hydrazido complexes can be isolated from many reactions that ultimately give ammonia if allowed to continue, e.g.. Equations... 

Recently, the first mechanistic study of the conversion of a coordinated dinitrogen to a hydrazido complex was reported/ Treatment of cis-[M(N2)2(PMe2Ph)4] with excess HCl, HBr, or H2SO4 in methanol yields [M(NNH2)(OMe)2(PMe2Ph)3] in a reaction that would ultimately give ammonia. The stoichiometry of the reaction is shown in Equation (27) ... 

The electrocatalytic properties of several parent dinitrogen or hydrazido-containing molybdenum and tungsten complexes with dppe ligand have also been investigated. Each of these complexes yielded NH3, in chemical yields which ranged from 1% to 36% per mole of complex.318... 

Their proton base strengths are less than that of the dinitrogen complex, but greater than that of the hydrazido(2 -) complexes.139 Their structures are likely to be similar to those of the alkyldiazenido complexes discussed below, that is trans octahedral with a linear MoNN system and NNH = 120°, but definite evidence is lacking. 

Both protonated and alkyl-substituted hydrazido(2—) complexes are readily available from the protonation or alkylation of coordination dinitrogen (equations 163 and 164). 

Treatment of dinitrogen complexes which cannot be separated. However diazenido complexes can be prepared cleanly by deprotonation of the corresponding hydrazido(2-) complexes with triethylamine or aqueous potassium carbonate (102), in a medium in which the products are insoluble. For example,... 

D. The Mechanism of Protonation of Dinitrogen to Form Hydrazido(2-) Complexes... 

Two studies on the mechanism of formation of hydrazido(2-) complexes by the reaction of dinitrogen complexes with acids have been reported (186,187). The salient features of these two mechanisms (one found in methanol, the other in tetrahydrofuran), will be discussed separately, and then compared. 

The more basic the phosphine coligand the greater the electron density imparted to the metal. This has two major effects on a coordinated dinitrogen a decreased lability to dissociation, and an increased basicity. In the formation of hydrazido(2-) complexes in tetrahydrofuran,... 

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