Nitrous nitrosyl complexes

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The decomposition of nitrosyl complexes has frequently been observed in acid solution, giving nitrous oxide, nitrogen or even ammonia. Here protonation must occur at the oxygen atom which is then removed as water. Further reaction gives gaseous products. An example9 is shown in equation (26). 

The pH dependence of the rate of formation of a nitrosyl complex shows that nitrous acid is the reactive intermediate in the reaction when the pH is in the range of 2-8. The catalysts are not deactivated during repeat cycles between their oxidized and reduced states. The catalyzed reduction appears to depend on the ability of the multiply reduced heteropolyanions to deliver electrons to the NO group bound to the iron center. 

Many ruthenium nitrosyl complexes are well characterized and appear to act as NO+ carriers. For example the bipyridyl complex [Ru(bipy)2(NO)Cl] + reacts with azide ion to give the aquo complex, nitrogen and nitrous oxide... 

Table 1 summarizes the most important surface complexes formed when NO and CO are adsorbed on noble metal catalysts. According to the literature NO and CO are adsorbed as nitrites, nitrates and carbonates on alumina [2]. The most important surface complexes for CO and NO adsorption on rhodium are a gem-dicarbonyl (Rh(CO)2) and a linear Rh-NO complex [1]. However, tricarbonyl and bridged Rhx-CO complexes have been proposed to be formed and different kinds of linear Rh nitrosyl complexes are possible [1-4]. The adsorption of CO on R and Pd catalysts depends much on the oxidation stage of R and Pd [5]. CO adsorption on R forms mostly linear and bridged carbonyls [6-11]. NO is adsorbed linearly on R [12]. In the case of Pd the most common surface complexes are linear carbonyls [13], strong multilaterally-bonded carbonyls, bridged carbonyls [5,14,15] and triply-bonded CO [5]. Isocyanate, nitrous oxide or nitrogen dioxide are proposed to be coimected to the reaction mechanism of the NO-CO reactions [2,16-19]. 

Good linear plots of the pseudo-first order rate constant for the formation of Cyt from Cyt as a function of [OH ] have been found, supporting the above mechanism. Although no evidence for the N-bound nitrous acid intermediate complex was found, the /jqh values derived from the slopes, together with the redox potentials for nitrosyl reduction in the heme compounds are in fair agreement with the general behavior observed for the electrophilic reactions of other nitrosyl complexes, including NP (see below) (51). 

The kinetics of formation of nitrosyl complexes of iron(n) from the reaction between ferric anide and nitric and nitrous acid in strongly acidic solution have been reported. These reactions involve reduction of iron(m) to iron(n) and oxidation of cyanide ion to cyanate ion. The ferricyanide is attacked by NOj which is formed from the following rapid equilibria ... 

Nitrous oxide gas reacts with the anionic cluster [Ru3(GO)9(G2R)] (R = /-Bu or SiMc3) to give the neutral nitrosyl complex Ru3(GO)9(G2R)(/x-NO) 112, the molecular structure of which has been determined. ... 

A study of reaction of 3-chloro-pentane-2,4-dione and 3-ethyl pentane-2,4-dione with nitrous acid in aqueous micellar solutions has concluded that nitrosation occurs initially on the enol-oxygen with the release of a proton to form a chelate-nitrosyl complex intermediate in steady state. ... 

Nitrosyl chloride [55], nitrosyl fluoride-hydrogen fluoride liquid complexes (NOF3HF, NOF 6HF) [56], nitrous acid-hydrogen fluoride solutions [57, 5 ] nitrogen trioxide (prepared in situ from nitric oxide and oxygen) [59] and rert-butyl nitrite-hydrogen fluoride-pyndine [60] have been substituted for sodium nitrite in the diazotization step... 

Fig. 4. Reductive nitrosylation of ferrihemes. Proposed formation of FenNO + as a precursor for nucleophilic attack of OH forming the bound nitrous acid intermediate. The release of nitrite forms a labile Fe11 species which binds NO forming the inert FenNO complex.

Miller and Meyer, 1971). The gaseous products are the same as those derived from the reaction of nitrous acid with azide ion. The reaction is kinetically first order in each reactant, and it is likely that an intermediate complex is also formed in this case. Similarly a p-nitroso complex is formed from the same ruthenium nitrosyl and N-methylaniline, possibly by initial... 

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