Ligand structures diazenes

The resuits obtained from cyclic diazenes and iron carbonyls serve as an example to discuss the modes of coordination of an isolated N=N bond30 62 46 19 As predicted from the electronic structure of these ligands, a-coordination via the orbital is usually favoured over 7T-coordination. Only if the metal is a very good 7r-donor (see Table 8) and the diazene a good jr-acceptor, like azobenzene, will stable 7T-com-plexes be favoured. Thus the first reaction step usually affords the o-N-tetracarbonyl... 

Regarding the structure and function of nitrogenases in producing ammonia from N2, Sellmann has studied several model systems wherein heterolytic activation of H2 occurs on sulfur ligands (87). A core geometry based on a hybrid of the FeMoco active site structure with a dinuclear diazene complex, [Fe( NHS4 )]2(p-N2H2), is a proposed model (Scheme 4). 

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