Dinitrogen mononuclear complexes

The formation of ammonia and/or hydrazine by protonation of binuclear bridging dinitrogen complexes of Groups IV and V is well established and has been reviewed elsewhere (82, 148). In general, stoichiometries are fairly well defined [Eq. (51)], although as with mononuclear complexes, mechanisms are not clearly understood (282). 

At lower temperatures dinitrogen coordinates to [RhH(PCy3)2] forming the four-coordinate mononuclear complex [RhH(N2)(PCy3)2].46,47 49 55 56... 

The reactions of dinitrogen in its mononuclear complexes (J. Chatt, J. Organometallic Chem., 1975. 100, 17). Non-enzymatic simulation of nitrogenase reactions and the mechanism of biological nitrogen fixation (G. N. Schrauzer, Anyew. Chem. Internal. Edn.. 1975. 14. 514). 

For the dinitrogen-metal complex either a mono- or binuclear complex (see Sect. 3.3) must be considered. Both types are well-known, and protonation has been investigated (mononuclear complexes Henderson et al., 1983, 1989 Shilov, 1992, and references therein binuclear complexes Dilworth et al., 1990 Henderson et al., 1990 Henderson and Morgan, 1990 Shilov, 1992 Blomberg and Siegbahn, 1993). In a review, Henderson (1990) illustrated the range of binuclear species that contain nitrogenous residues from the mono- to the tetra-protonated forms. 

TiCp 2], generated as indicated above, binds molecular nitrogen giving two forms, monohapto and dihapto of a mononuclear complex that can be protonated to hydrazine (a rare case of transition-metal-induced reduction of dinitrogen). 

The reactivity of coordinated dinitrogen in mononuclear complexes is still not yet fully understood. The reactive complexes are those at the left-hand end (Groups 4, 5, and 6) of the transition series and the reactions are best developed in the case of complexes of molybdenum and tungsten. The first reaction discovered was an acylation of coordinated nitrogen, but it was quickly recognized that protonation is equally, if not more, facile. " ... 

Mononuclear 18-electron dinitrogen complexes generally undergo successive reversible one-electron oxidations to moderately stable 17-electron and unstable... 

Figure 18 Proposed conversion of dinitrogen to ammonia at a mononuclear site, based on structurally characterized complexes.

An alternative route to the mononuclear dinitrogen complex is by the reaction of [(ij5-CsH5)Mn(CO)2(N2Ari r and its rhenium homologs with nucleophiles such as Cl, Br, I, Cn, and SCN. This has poten-... 

Generally, when dinitrogen complexes are treated with acid the strongly reduced metal is protonated, leading to oxidation of the metal and formation of a hydrido complex. This is accompanied usually by loss of dinitrogen and often by subsequent protic attack on the hydride to evolve dihydrogen (7). Of the stable mononuclear dinitrogen com-... 

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