N2 Complexing

N2 Complexing. LCAO-MO calculations have been made on the electronic structures of the complexes M,N2 (M = H, Li, Be, or B ), N2,BX3 (X = F or H), and M,N2M (M = H, Li , B , or BH3). The calculations were used to discuss models of nitrogen fixation by enzymes in biological systems. Quantum mechanical calculations by the CNDQ/2 method confirm the possibility of N2 complex formation with Li and F ions. The contribution of covalent bonds to the energy of the complexes has been analysed and their lability discussed.  

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CgH )P[CH2CH2P(CgH )2]2, and the labiHty of a simple phosphine, a cycHc system has been devised ia which the product, MoBi2(ttiphos), can be used to prepare the starting Mo—N2 complex again (195). 

An example of a serendipitous discovery in a field related to diazo chemistry is the first in vitro product of a reaction of molecular nitrogen with a transition metal complex (Allen and Senoff, 1965). As discussed in the context of diazo-metal complexes (Zollinger, 1995, Sec. 3.3), the metal —N2 bonds are similar to C —N2 bonds in organic diazo compounds. The paradigm that N2 is (almost) inert in chemical reactions probably explains why it took so long for N2 complexes to be discovered. ... 

This section on N2 complexes concludes with a brief mention of a Mossbauer study of the Fe/N2 system (8). The N2 stoichiometries were... 

Forming a hydrogen bond between (i )-homocitrate and His 442 could effectively release electron density into the cluster. Studies on structurally defined N2 complexes have shown that the binding of N2 to a metal site and its ability to be protonated are favored by electron-rich sites. Thus, it is postulated that the electron-richness of the... 

We have recently prepared some new and very thermolabile CO- and N2 comPlexes derived from titanocene [1] or decamethyltitanocene [2], and have characterized them by their vibrational spectra. As well as "classical" matrix spectroscopy, we have used spectroscopy in liquid xenon (LXe). The application of chemistry and methodology indicates the decamethylsilicocene structure, which represents the first example of a stable jt-complex of divalent silicon [3]. Reaction with CO or N2 leads to the two title complexes [4] ... 

Holland and Peters earlier reported examples of three- and four-coordinate N2 complexes with iron in the formal +1 oxidation state, but in neither case were terminally bonded N2 species identified or isolated dinuclear end-on Fe-NN-Fe species were inevitably obtained (99,100). Therefore, Peters and coworkers recently began to turn their attention to new derivatives of the classic Sacconi-type tripodal ligands to achieve access to a terminally bound Fe-N2 complex. Indeed, by employing the mono-anionic ligand L8 — [f2-Ph2PC6H4)3Si] (Fig. 10) they were able to generate the desired complex [Fe(L8)(N2)] (10) (101). 

It was found that the stability of the mixed complexes increased considerably with the number of ethylene ligands. More exactly, the Li(C2H4)2(N2) complex was stable up to the temperature at which the rare-gas matrix sublimed. It was identified and described as a Li(C2H4)2 complex with two equivalent ethylene ligands, slightly perturbed by the addition of a N2 molecule (Scheme The comparison of the IR spectrum... 

Interestingly, formation of (23) was accomplished by cyclization of (210) on a catalytically fixed N2 complex <920M4ll6>. An unconventional cyclization to the azasilacyclopentene system was achieved in high yields by amination of cis l-boryl-2-silylethylenes (219) with sodamide <81AG1009, 87CB669, 88CB597). 

Examples of the former criteria are as follows metal centers with a low electron-richness (high Eg) bind preferably ligands that are strong electron donors (low Pi values) coordination of N2 is favored by a high electron-richness (low Eg) and a high polarizability (P) of the metal center [10, 11]. Tr ns-[ReCl(N2)(dppe)2] is an example of a rather stable N2 complex with such features (the Eg and p values of the binding metal center are 0.68 V and 3.4, respectively [21]). 

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