Dinitrogen complexes, reviews

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). 

Finally, a racemic cyclopropanation process has also been developed that utilizes an iron Lewis acid catalyst (72) that presumably proceeds through an iron carbene intermediate (73) (Scheme 28). The catalyst is activated by reaction with diazo compounds to produce an intermediate (74) that loses dinitrogen see Dinitrogen Dinitrogen Complexes) to afford the cyclopropane. This chemistry has been extended to the production of epoxides and aziridines and has recently been reviewed. ... 

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]). 

Besides this iron-nitrosyl complex, nitrosyl complexes of other transition metals can be used for nitrosation. As discussed by Bottomley et al. (1973, see also review by Bottomley, 1978), these complexes are not only sources of nitrosyl ions (NO" ) as two-electron acceptors, but also of nitroxide (NO ) as one-electron donor. Bottomley found that they are nitrosating reagents only if their NO stretching frequency is greater than 1886 cm The ruthenium nitrosyls are particularly interesting with respect to their reaction with aliphatic and aromatic primary amines. We discuss them in the context of metal dinitrogen complexes (Sect. 3.3). 

Metal — dinitrogen complexes are discussed briefly in this book, because they are structurally related to diazo and diazonium coupounds. In these complexes a diazo group is bonded to a metal and not to a C-atom, as in organic compounds. Addition products of aliphatic and aromatic diazo compounds will be reviewed in Chapter 10. 

Since the pioneering work of Allen, Senoff, and Shilov et al., dinitrogen complexes have been synthesized with the majority of transition metals. Numerous reviews have been published. Because of the rapidly growing literature, we will only mention summaries published since the mid-1980 s (Colquhoun, 1984 Pelikan and Boca, 1984, 1985 Leigh, 1986, 1991 Johnson et al., 1987 Hidai and Mizobe, 1989 Henderson, 1990 Shilov, 1992a Hidai and Mizobe, 1993). 

From our knowledge on structure and reactivity of the dinitrogen molecule, e. g., the very high dissociation energy of the triple bond (940 kJ mol ), it is obvious that the major problem is not the formation of the diazenido complex (1), but the consecutive steps (2)-(4). In particular, it is unlikely that diazene (HN=NH) is an intermediate, as it is thermodynamically very unfavorable. Chemical research on nitrogen fixation concentrated, therefore, in recent years on reduction mechanisms of dinitrogen complexes (see review of Shilov, 1992). 

In limiting this chapter to metal-phosphine complexes, many significant compounds and nitrogen-fixing systems will not be discussed. However, interested readers are referred to a number of relatively recent reviews of the chemistry of nitrogen fixation. " Similarly, adequate descriptions of the bonding and physical properties of the metal dinitrogen complexes have appeared elsewhere and will only be mentioned in this chapter where relevant. 

There are no dinitrogen complexes of any of these metals that contain a phosphine ligand. The considerable amount of nitrogen-fixing chemistry reported for titanium, and to a lesser extent zirconium, involves alkoxide, cyclopentadienyl, and halide complexes.The catalytic nitriding reactions of titanium will be reviewed in Section 3. 

A. Ozaki, K. Aika Catalytic Activadon of Dinitrogen The third chapter is a comprehensive and critical review of studies on the catalytic activation of dinitrogen, including chemisorption and coordination of dinitrogen, kinetics and mechanism of ammonia synthesis, chemical and instrumental characterization of active catalysts, and homogeneous activation of dinitrogen including metal complexes (353 references). 

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. 

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