Nitrosyl reaction + metal atoms

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

In contrast to nitrosyls, the absence of a transferable oxygen atom in N2R ligands allows the preparation of stable diazenido complexes of oxophilic, early transition metals see for example Cp2TiCl(N2Ph). Furthermore, there are as yet no diazotate (RN=NO-) forming reactions anolo-gous to the nitrite forming reactions in nitrosyl chemistry (see equations 112 and 113). 

As in mononuclear nitrosyl complexes, it is convenient to separate the reactivity into two sections (1) reactions directly involving change at the NO, and (2) reactions of the metals that are enhanced by the presence of the nitrosyl ligand. The reaction of overwhelming importance that occurs with cluster coordinated nitric oxide is deoxygenation. Depending on the conditions this can ultimately sdeld NH, NH2, NCO, or simply N atoms coordinated to the cluster. 

One electron oxidation of NO generates the nitrosonium cation (N0+). In this reaction, the iron atom of Fe(III)-containing metalloenzymes acts as the electron acceptor. The metal-nitrosyl complex formed (Fe(II)-NO+)... 

Although the protonated TMH or TMD complexes as formulated above have so far never been observed directly, and are just postulated intermediates, there exists experimental evidence that the dinitrosyl hydride complexes posses a strong basic site at the atom. For example, we were able to characterize A—ON-ReH(NO)(P Pr3)2 adducts, A representing a Lewis acid like BF [52] or even the cationic metal fragment [Re(NO)2(P Pr3)2] itself [50]. The formation of these adducts not only illustrates the basicity of the nitrosyl group, but also the strong Lewis acidity of the 16e cation. We also found that the bimetallic complex shows a similar reactivity as the free cationic species itself. Further evidence for the proposed heterolytic splitting was obtained when the reaction with H2 or D2 is performed in the presence of an external base (Scheme 5). 

The reactivity of metal nitrosyl complexes (51) with thiols is of particular concern in the mobilization of NO to make it accessible for the vasodilation process. Very recently, it has been reported (52) that the S-atom of cysteine reacts to bind the N-atom of the nitrosyl complex of Ru-edta to form a 1 1 intermediate species. Stopped-flow kinetic studies revealed the formation of a transient species, whose rate of formation was found to be first order with respect both [Ru (pac)(NO)] and RSH. The values of rate constants ( 1) were formd to be in the range (0.2-5) x 10 M s at 25°C. Considering the spectral features and kinetic behavior of various [Ru (pac)(SR )] and [Ru (pac)NO] species as described in the preceding sections, and analysis for the products of the above reaction (N2O), the following mechanism (Scheme 15) for the redox reactions involving electron transfer fi om thiols to coordinated NO, that results in the formation of disrdfide (RSSR) and N2O, has been proposed for the reaction of [Ru (pac)(NO)] with thiols (RSH). 

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