Of coordinated azide

Hydrazinofluorophosphines, 13 393 Hydrazoic acid, 9 134 reaction mechanisms, 22 131-135 of coordinated azide ion, 22 133-135 oxidation by metals, 22 131, 132 by nonmetals, 22 132, 133 thermal decomposition of, 14 121 Hydrides... 

This subject should not be left without noting that some aspects of the work are very arduous. Though it is often easy to design experiments which if performed would demonstrate one point or another, the work which they entail can be very difficult because the substances required are difficult to prepare. New synthetic procedures are needed badly. One now being developed by A. Sargeson, which depends on the removal of coordinated azide by NO+ in the presence of a nucleophile, promises to be useful for a number of preparations. 

Table IV. Summary of Coordinative Azides and Molecular Azides... 

Basolo et al, have also reported (36) their investigations of the add-catalyzed decomposition of coordinated azide. They find that the primary decomposition product is a protonated nitrene... 

Fragmentation of coordinated azide ligands can occur under the redox conditions associated with ESI (Scheme 6.9) [99] or via collisional activation of metal azide complexes(Scheme 6.10) [94, 100-102]. 

With the same tactic, a meta-stable 3-coordinate iron(III) imido complex was reported by Holland and coworkers [40]. Using the diketiminate-supported dinitrogen iron(I) complex [L T eNNFeU ] as a source of iron(I) precursor [L = 2,4-bis (2,6-diisopropylphenylimino)pent-3-yl], the addition of adamantyl azide (AdN3) in... 

Other iron-imido complexes have also been reported. Holland and coworkers reported the synthesis of the imidoiron(III) complex [L FeNAd] [40, 41]. This imidoiron(III) complex has not been isolated and was found to convert to a purple high-spin iron(III) complex. It has an S = 3/2 ground state from EPR measurement. Based on the results of QM/MM computations, [L EeNAd] is a three-coordinated complex with an Fe-N distance of 1.68 A and has a nearly linear Fe=N-C unit with Fe-N-C angle of 174.1°. Chirik and coworkers made use of liable ligands to prepare iron-imido complexes by treatment of C PDI)-Fe(N2)2 ( PDI = (2,6- Pr2CgH3N = CMe)2C5H3N) with a series of aryl azides [47]. 

Whereas heating [Pt(terpy)(N3)]+ in the gas phase gives dinitrogen, heating in solution in acetonitrile or benzonitrile gives the tetrazolato complexes 14 (R = Me, Ph), presumably by nucleophilic attack by RCN at coordinated azide and subsequent closure of the N4C ring (401). 

A set of SER spectra for adsorbed azide on silver, obtained for the same surface and solution conditions and for a similar sequence of electrode potentials as for the PDIR spectra in Figure 1, is shown in Figure 2. (See the figure caption and reference 7 for experimental details.) Inspection of these SER spectra in comparison with the PDIR results illustrate some characteristic differences in the information provided by the two techniques. Most prominently, in addition to the Nj" j/as band around 2060 cm"1, the former spectra exhibit three other features at lower frequencies attributable to adsorbed azide vibrations. By analogy with bulk-phase spectra for free and coordinated azide (15), the 1330 cm"1 SERS band is attributed to the N-N-N symmetric stretch, vt (2). The observation of both i/a and j/aa features in the SER spectra differs from the surface infrared results in that only the v band is obtained in the latter (2). The appearance of the vn band in SERS is of interest since this feature is symmetry forbidden in the solution azide Raman spectrum. 

Examination of the azide bending-mode region (600-700 cm 1) in the SER spectra (Figure 2) is also instructive with regard to adsorbate orientation. Thus, the pair of bands (at ca. 610 and 670 cm"1) seen at the least negative potentials are characteristic of end-on coordinated azide (15) the loss of the lower-frequency partner for E < -0.15 V is therefore also indicative of the removal of azide bound in this adsorbate geometry, again in harmony with the interpretation of the infrared spectra (7). 

On the basis of DFT calculations, a catalytic cycle involving a copper vinylidene intermediate has been proposed (Scheme 9.22) [44]. The reaction is initiated by copper acetylide (138) formation. Sharpless and coworkers next invoke an unusual [3 + 3]-cycloaddition that would be forbidden by orbital symmetry, were it not stepwise. Coordination of an azide to complex 138 generates a zwitterionic complex (139). Internal nucleophilic attack of the acetylide moiety of 139 on the electrophilic... 

Ligands that can coordinate to an active center in an enzyme and prevent coordination by the substrate will tend to inhibit the action of that enzyme. 1 We have seen that azide can occupy the pocket tailored to fit the carbon dioxide molecule. This prevents the latter from approaching the active site. Furthermore, the infrared evidence indicates that the azide ion actually does bind the zinc atom The asymmetric stretching mode of the azide ion is strongly shifted with respect to the free ion absorption. Thus the zinc is inhibited from acting as a Lewis acid towards water with the formation of a coordinated hydroxide ion. Other inhibitors also bind to the metal atom. As little as 4 x I0-6 M cyanide or hydrogen sulfide inhibits the enzymatic activity by 85%. 

In the square pyramidal complex [Ni(Me4cyclam)N3](C104) (379) (Me4cyclam is 1,4,8,11-tetramethylT,4,8,ll-tetraazacyclotetradecane) the coordinated azide anion is on the same side of the four methyl groups with the nickel atom 33 pm from the N4 plane. The five- and six-membered chelate rings are in the usual gauche and chair conformations respectively.2681 This complex is labile in comparison with the very inert dinuclear complex... 

Coordinated azide ion will undergo a number of reactions which involve attack at the azide ligand. A number of examples are summarized in Scheme 9.1172-1175 The azide ligand is photochemically dissociated from bis azide complexes. Irradiation of Pt(CN)4(N3) gives Pt(CN)4 and the azide radical (equation 366),1176 whereas with Pt(N3)2(PPh3)2 the nitrogen-containing product is believed to be N6 (equation 367).1177... 

The coordinated azide undergoes addition reactions with a variety of unsaturated compounds. Thus with carbon monoxide under very mild conditions the azide is converted to isocyanate with the loss of nitrogen (equation 17).293-295... 

Reactions between 5-cyanotetrazole and transition metals, when performed in boiling acetone, lead to hydrolysis of the cyano group and formation of 5-carbamyl tetrazolate complexes (68). Complexes containing 1- or 5-substituted tetrazolate anions can also be obtained by 1,3-dipolar cycloaddition of organic isonitriles (RNC) (15) or nitriles (RCN) (61), respectively, to coordinated azide ligands [Eqs. (3) and (4)]. 

Azide complexes containing terminally,257,262 l,l-/i-219 as well as 1,3- -bonded25S coordination modes have been reported. In [NEt4][Mn2(N3)3(CO)6]219 all three azide groups are 1,1- -bonded. Mn(acac)2(N3) is a coordination polymer as a result of l,3-/r bridging of the azide groups between [Mn(acac)2]+ cations, cf. (92). 

Freshly prepared a s-[Ru(en)2(N8)2]PFt is paramagnetic (/i. = 2.0 B.M.). In the air at room temperature the purple-red crystals decompose over a few days to a dark brown mixture of cis-[Ru(en)2(N2)(N8)]PF6 and unknown nitrosyl ruthenium species. It may be stored in the dark at — 15°C. for several weeks without significant change. Its i.r. spectrum shows a characteristic coordinated azide-ion band at 2050 cm.-1. Most samples also show a sharp weak peak at 2130 cm.-1, which is due to the presence of small amounts of cis-[Ru(en)2(N2)(N8)]PF. CTs-[Ru(en)2(N8)2]PF8 is readily soluble in water and dimethyl sulfoxide, in which it is initially a typical 1 1 electrolyte. Subsequent complex chemical changes occur in these solvents. In acetone, methanol, and acetonitrile, however, as-[Ru (en) 2 (N8) 2]+ converts cleanly and quantitatively to cis-[Ru(en)2(N2)(N8)]+. 

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