Dinitrogen, complexes with

IV. Molybdenum Dinitrogen Complexes with Polydentate Phosphine... 

The alternative mechanistic scenario for the protonation and reduction of end-on terminally coordinated N2 through the Schrock cycle is represented by the Chatt cycle which has been developed many years earlier (5). This system is based on Mo(0) and W(0) dinitrogen complexes with phosphine coligands (Fig. 3). As expected, the intermediates of the dinitrogen reduction scheme are very similar to those of the Schrock cycle. Moreover, a cyclic generation of NH3 from N2 has been demonstrated on the basis of this system, however, with very small yields (3,4a). In order to obtain general insight into the mechanism of the Chatt cycle we have studied most of the intermediates of Fig. 3 with... 

Fig. 8. Mo/W dinitrogen complex with the P/N ligand N,N,N, N -tetrakis-(diphenylphosphinomethyl)-2,6-diaminopyridine (pyN2P

Nitrosyls are included in Section 35.4.2.6 and dinitrogen complexes with the phosphorus donors immediately below. 

This remarkable reaction with azine may be compared to an azine-forming reaction of at least two dinitrogen complexes with acetone. 

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 increased basicity of a ligand when coordinated to the heavier metals in a transition metal triad has been appreciated for some time (311). This is manifest in (1) the rate of alkylation of alkyldiazenido complexes (kw/kMo = 5.4) (93), and (2) the rate of formation of hydra-zido(2-) complexes by the reaction of dinitrogen complexes with acid, in methanol ( w// Mo = 9.2 x 102) (186), and in tetrahydrofuran (kw/ kMo = 29-85, dependent upon the acid and substrate employed) (187). Clearly the electron-releasing capability of the metal has conflicting influences on the rate, but as in Section VI,El the basicity influence dominates. 

Recently, a first complex containing a M=Pb triple bond has been reported and this was obtained by the reaction Mo dinitrogen complex with aryl lead bromide in tolnene at ambient temperature according to equation (18). ... 

Figure 2. Typical structures of dinitrogen complexes with transition metal compounds (M = metal -I- other ligands).

Dinitrogen Complexes with Transition Metals Possible Catalysts for N2 Reduction... 

Since 1965, when the first dinitrogen complex with ruthenium(II) was discovered [3a] N2 complexes with several transition metal compounds have been prepared. As with other unsaturated molecules, in these complexes dinitrogen acts both as electron donor and electron acceptor, the latter properties being more pronounced. Different kinds of complex are obtained experimentally and considered theoretically (e.g. see review [3b]). 

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