Dinitrogen complexes with transition metals

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... 

They, in contrast to Kishi and Roberts (52) and Johnson and Roberts (55), interpret the N(ls) peak at 405 eV as a satellite of the 400-eV peak moreover Fuggle and Menzel observe two components to the 400-eV peak, one at 399.1 eV and the other at 400.4 eV. These they attribute to the two nonequivalent nitrogen atoms in a vertically adsorbed Nj molecule and draw the analogy with the splittings observed in dinitrogen complexes of transition metals. The question that is immediately raised is the interpretation of the relatively high intensity of the satellite peak, some 60% of the main peak. Fuggle et al. (56) have considered this point. 

The discovery that dimtrogen was capable of forming stable complexes with transition metals (Chapter 5) led to extensive investigation of the possibility of fixation via such complexes. An imporiant development was the discovery that certain phosphine complexes of molybdenum and tungsten containing dinitrogen readily yield ammonia... 

It should be mentioned that consecutive two-electron reduction of dinitrogen is still usually considered likely in the literature, with diazene, N2H2, as an intermediate but stabilized by complexation with transition metals. At the same time there is no doubt that both 7r-bonds of N2 can be used simultaneously for four d-electrons (entering two degenerate 7ig -orbitals) from one, two, or several metal atoms forming a complex with dinitrogen, and separate cleavage of each 71-bond seems to be unnecessary, more so because it is thermodynamically unfavorable. Therefore, for-... 

Since the first step of all of these reactions is dinitrogen coordination to either the surface of the catalyst or transition metal center of the complex, let us briefly discuss the nature and importance of the M-N2 interaction, and the possible coordination modes ofN2 to transition metal centers. These issues were the subjects of many discussions in the literature [10, 11] and it is commonly agreed that the interaction of the N2 molecule with transition metal centers facilitates the activation of the N=N triple bond the stronger the M-N2 interaction, the easier to break the N=N triple bond. 

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. 

Table 4 Di- and Tri-nucleai Dinitrogen-bridged Complexes of Rhenium(I) with Transition Metals... 

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]). 

Until today, it is a general rule that 1 1 adducts of diazoalkanes with transition metals are unstable in most cases. The stability can be significantly increased if dibenzoyldiazomethane is used as ligand. This was demonstrated by Cowie et al. (1986 a) in the synthesis of iridium complexes. As shown in (10-20), dibenzoyldiazomethane replaces the dinitrogen ligand in the starting material. The reaction is run... 

In 2004 and 2005 the photochemical activation of dinitrogen with transition metal model complexes of the Sellmann type nitrogenase was studied using CPMD [193, 194], A dinuclear complex — designed to emulate the open-side FeMoco model -was simulated. Several side reactions were observed which have to be suppressed in order to arrive at the reduced species [194]. Chelate effects and their partial dissociation as well as low temperatures led to successful events. An optimized design of the complexes to inhibit side reactions was suggested [194]. 

Carbonyl, dinitrogen and cyanide complexes of transition metals are generally not stable unless the metal has lone-pair electrons occupying atomic orbitals that overlap with Ugand n orbitals. In structures (4)-(6), we have indicated two sets of lone-pair electrons. If we assume that these electrons occupy metal and... 

In this chapter we discuss host-guest complexes of arenediazonium salts with crown ethers and related compounds. Transition metal complexes of arenediazonium ions are treated together with those of dinitrogen and of diazoalkanes in our second book (Zollinger, 1995, Sec. 10.1). 

THE REACTIVITY OF TRANSITION METAL COMPLEXES WITH DINITROGEN... 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

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