Hydrazidium complexes

DFT calculations were performed on Mo dinitrogen, hydra-zido(2-) and hydrazidium complexes. The calculations are based on available X-ray crystal structures, simplifying the phosphine ligands by PH3 groups. Vibrational spectroscopic data were then evaluated with a quantum chemistry-assisted normal coordinate analysis (QCA-NCA) which involves calculation of the / matrix by DFT and subsequent fitting of important force constants to match selected experimentally observed frequencies, in particular v(NN), v(MN), and 8(MNN) (M = Mo, W). Furthermore time-dependent (TD-) DFT was employed to calculate electronic transitions, which were then compared to experimental UVATs absorption spectra (16). As a result, a close check of the quality of the quantum chemical calculations was obtained. This allowed us to employ these calculations as well as to understand the chemical reactivity of the intermediates of N2 fixation (cf. Section III). 

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

Fig. 11. Sections of the MO schemes of the hydrazidium complex IV (left) and the NNH2 complex III (right) along with isodensity surface plots of the corresponding MO s.

The resulting mechanistic cycle is shown in Figure 6.9. Analogous to the Schrock cycle, a strictly alternating sequence of protonation and reduction steps is derived. In the first half of the cycle the N-N bond is weakened step by step, leading to cleavage of the N-N bond and release of the first molecule of ammonia after formation of the hydrazidium complex. In the second half of the cycle, the Ru-N bond is progressively weakened and the... 

Complexes containing the diazenido and hydrazidium ligands as well as the hydrido-hydrazido(2-) moieties have been isolated directly or indirectly from 1, 2, and the N2 complexes with the related phosphine coligands (23,27). 

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