Hydrazido complexes Group

A general approach to rhenium hydrazido complexes is the reaction of oxo or chloro compounds with organohydrazines as has been demonstrated in an early report with the synthesis of [Re NNC(Ph)0 Cl2(PPh3)2] (310), " the molecular structure of which was solved in 1988. A detailed study on [Re(NNR)Cl2(PPh3)2] complexes with R = COPh or phthalazine shows that the course of subsequent reactions is governed both by the nature of the donor group R responsible for chelate closure and by the type of donor ligand introduced. No simple substitution chemistry has been observed for R = phthalazine. The benzoyl compound... 

There is only one reported mononuclear hydrazido(2—) complex for the titanium group, [Ti(r/5-CjHj)2(NNSiMe3)2].498 Other hydrazido complexes are known but involve bridging hydrazido groups (see below). For reasons not yet fully understood, titanium is apparently reluctant to form four electron metal-nitrogen multiple bonds. 

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. 

It is by no means certain that simple protonation of a hydrazido(2-) ligand at a mononuclear Mo(IV) or W(IV) site to give, for example, hydrazidol 1 -) or imido species (Scheme 15) can take place at all, particularly in view of reactions (45) and (47). Nevertheless, protonations of hydrazido(2-) groups to give imido, nitrido, or hydrazido(l-) species remain attractive pathways and indirect evidence from the reactions of orgcmohydrazido(2-) complexes gives them some plausibility. These are discussed below. 

We have made several other V" complexes by displacing the hydrazine ligand in [V(N2H4)(NS3)] with Cl , N3 CN , MeCN or CNBu , and have prepared a series of imido-complexes [V(NAr)(NS3)] (Ar = various substituted phenyl groups), and of hydrazido-complexes [V(NNR R )(NS3)] (R R = methyl or phenyl) from reactions of [V(0)(NS3)] with aryl isocyanates or 1,1-disubstituted hydrazines, respectively. Structural studies on several of these compounds always reveal trigonal bipyramidal coordination about the V atom. The V-N distance in the V(NS3) system, as a result of the shape of the NS3, is sensitive to... 

Hydrazido(2-) complexes, 2,141-151 bond lengths and angles, 2,145 bridging, 2,150 chemistry, 2,145 electrochemical reduction, 2,147 Group VI, 2,148... 

A very helpful attempt to classify organohydrazido and related complexes of Group 7 elements by analysis of their X-ray crystal structure data has been undertaken in a review which also covers the structural chemistry of this type of complexes up to the year 1996. The convention applied in this article will also be used here to classify hydrazido and related complexes. 

Transition metal hydrazido(2—) and (1 —) ligands form a distinctly different group of complexes. 

Extensive studies of the mechanism of formation of dialkylhydrazido(2—) complexes from [Mo(N2)2(dppe)2] (M = Mo, W) have revealed a free radial mechanism for addition of the first alkyl group with loss of one N2 molecule as the rate-determining step.484 Addition of the second alkyl group proceeds via an SN 2 mechanism (see Scheme 6) and the effect of the metal and coligands on reaction rates has been studied in detail.485 Acoyl and aroyl hydrazido(2 —) complexes can be obtained by reaction of the N2 complexes with acoyl or aroyl halides in the presence of acid (equation 177).486... 

Although it proved impossible to isolate (D) (in practice dihalides are isolated), other hydrazido(2-) complexes containing alkoxy groups have been obtained (259). 

Figure 3. Structures of some Group VI metal-N2 and hydrazido(2-) complexes (a) trans-Mo(N2)2(dppe)2 as determined in Ref. 44 (b) suggested stereochemistry of cis-Mo(N2)2(PPhMe2)4 from data in Ref 48 and 52 (c) [W(N2H2)Cl(dppe)2] + as determined in Ref 47.

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