Nitrosyl species

Experiments over Cu/ZSM-5, Centi and Perathoner[46] eoncluded that the thermal stability of adsorbed species increased with increasing oxidation state of nitrogen in nitrogen adspeeies. Valyon and Hall[41] also found that the nitrosyl speeies adsorbed on Co-ferrierite is weakly adsorbed compared to nitrate species. Therefore, the second NO desorption peak oeeurring at medium temperatures likely corresponds to the nitrosyl species, according to their thermal stability. 

Physically desorbed NO (pmolg ) Nitrosyl species (pmolg ) Nitrate species (pmolg ) Total (pmolg ) Total (pmolm )... 

Co-, Mn-, and Fe-based perovskites, NO peaks appearing at similar temperatures as those in NO-TPD experiments (apart from a minor desorption at medium temperature and an intense one at high temperature) were also found and aseribed to the desorptions of physically adsorbed NO, nitrosyl species and nitrate species in the order of their thermal stability. The NO peaks obtained at low (80-110 °C), medium (200-210 °C), and high (310-390 °C) temperatures in the present NO-TPD analyses were thus correlated to physically adsorbed NO, nitrosyl and nitrate species. 

Second, the results obtained from the MoCl2(NO)2(4-Etpy)2/ (CH3)3A12C13 system indicate that the interaction of organoaluminum and complex occurs in several stages. A rapid, initial step in which the vN0 bands are shifted to higher frequency is followed by a slower step in which the first-formed species is converted to a second nitrosyl species with vno bands at lower frequencies and a final step in which the NO groups are lost from the molybdenum. 

The number of iron-selenium-nitrosyl complexes is substantially smaller than the iron-sulfur-nitrosyl species, as considerably less work in this area has been reported. However there are a number of differences between the sulfur systems and their analogs containing selenium or tellurium. For selenium it is convenient to divide the complexes into three classes, dependent upon the stoichiometry of the metal-chalcogen framework. 

In (95), the initial formation of the bent nitrosyl species [Co(NO)(en)2Cl]+ (220) is followed by electrophilic attack of free NO and then by reaction with a second NO molecule leading to products. Since the nitro complex produced in this reaction has the same stereochemistry as the reactant Co111—NO- species, it has been proposed that the Co—N(nitrosyl) bond remains intact throughout the reaction sequence, thus requiring free NO to attack via its oxygen end (193). This proposal requires further proof. 

The full account of the preparation and subsequent reactions of the cationic nitrosyl complexes [M(NO)(CO)3(diphos)]PF6 (M = Mo or W) has been published. These complexes react with NaX (X = halide, S2CNMe2, or S2CNEt2) salts to form the corresponding [M(NO)(CO)2(diphos)X] derivative. With phosphine ligands (L) in CHC13, [M(NO)(CO)L(diphos)Cl] is obtained, but in acetone, [M(NO)(CO)2L2-(diphos)](PF6),(acetone) and [M(NO)(CO)(diphos)2](PF6) are formed. Decarbonyla-tion occurs when [Mo(NO)(CO)3(diphos)](PF6) is heated under reflux in CHC13 to produce [Mo(NO)(diphos)Cl2] and other polynuclear nitrosyl species.320... 

The adsorption of NO on morphologically well-defined samples has not been investigated in detail. On high-surface-area materials (509, 510), stable nitrosyl species are formed together with disproportionation products (N20 and N02) this complex chemistry renders the interpretation of the resulting (complex) spectra difficult (unpublished results). However, the... 

Reactions of NO were also studied with the synthetic heme protein discussed earlier, namely the recombinant human serum albumin (rHSA) with eight incorporated TPPFe derivatives bearing a covalently linked axial base, were also investigated. The UV-vis absorption spectrum of the phosphate buffer solution at physiological pH showed absorption band maxima at 425 and 546 nm upon the addition of NO to form the nitrosyl species, which was also formed when the six-coordinate CO-adducts were reacted with NO gas. EPR spectroscopy revealed that the albumin-incorporated iron(II) porphyrin formed six-coordinate nitrosyl complexes. It was observed that the proximal imidazole moiety does not dissociate from the central iron when NO binds to the trans position. The NO-binding affinity P1 /2no was 1.7 X 10 torr at pH 7.3 and 298 K, significantly lower than that of the porphyrin complex itself, and was interpreted as arising from the decreased association rate constant (kon(NO), 8.9 x 10 M s" -1.5 x 10 M s ). Since NO-association is diffusion controlled, incorporation of the synthetic heme into the albumin matrix appears to restrict NO access to the central iron(II). ... 

The most complex interactions are observed in ternary iron-sulfur-nitrosyl systems. Depending on the bond nature, the ternary iron-sulfur-nitrosyl species may be classified into two groups (i) iron complexes with the S-nitrosothiol ligand containing the [Fe—N(SR)0] moiety and (ii) RS—Fe—NO compounds, where both NO and sulfur are coordinated to the Fe-center. Irrespective of the structural details, the mutual interactions of all components are very strong due to considerable bond delocalization within both ternary systems. 

Alkylation of thioamides with Meerwein s reagent (trialkoxonium fluoroborate) proceeds via a thioiminoester and subsequent base hydrolysis with sodium carbonate (equation 32). For the synthesis of 2-pyridones from 2-thiopyridones, chloroacetic acid has been used. ° Mild reaction conditions are provided by nitrosyl species which are derived from a variety of reagents excess NaNOa/HCP in aqueous medium, nitrosonium tetrafluoroborate in dichloromethane, dinitrogen tetroxide in acetonitrile at low temperature and f-butyl thionitrate. ... 

This reaction path was first observed in the three-coordinated cP complex, Mo(NRAr)3 (R = C(CD)3)2Me, Ar = 3,5-C6H3Me2), upon reaction with N20 in degassed Et20, at 25 °C. The products were the crystalline nitrido-complex, MoN(NRAr)3, and the nitrosyl species, Mo(NO)(NRAr)3, in a 1 1 ratio. The only precedent for N=N cleavage is the stratospheric production of NO upon reaction of N20 with 0(1D).12°... 

Indeed, the wavenumber of bent species has been observed to be less than that of linear nitrosyl species (48). 

The ability of Pd-H-ZSM-5 catalysts to form Pd(I) nitrosyl species was related to their specific behavior of selectively reducing NO to N2 (25). This statement finds support in the curve of NO conversion versus Pd content (Figure 7A). Indeed, for reaction temperatures less than 500°C, NO conversion clearly increases with Pd content, in a manner similar to the amount of Pd nitrosyl complexes versus Pd content. Above 500°C, volcano shape curves are observed and NO conversion decreases for Pd content higher than 0.5 wt.-%. This can be easily explained by the simultaneous total conversion of CH4. The absence of reductant in the feed is expected to decrease the rate of NO reduction. This implies that CH4 participates to two distinct reactions, SCR reaction and methane combustion by O2, which compete at high temperatures. This competition is confirmed by the selectivity results, which indicates that the combustion is strongly favored above 500°C. The question arises to know whether these two reactions are catalyzed by the same types of sites. 

Samples of RuCl3 rH20 may contain Ru(IV), various oxo-and hydroxychloro-complexes, and nitrosyl species. Also, considerable variation in reaction times and product distribution may accompany the use of samples from different sources.4 In this synthesis, consistently high yields of [Ru(bipy)3]Cl2 can be obtained if the RuC13 xH20 is oven treated prior to use. 

In much the same way that cobalt-dioxygen systems are paramagnetic (S = 5) and amenable to EPR studies, iron-nitric oxide (also called iron nitrosyl) species are also paramagnetic and isoelectronic with cobalt-dioxygen species. The unpaired spin is localized mostly on the NO group. 

NO molecule was then used in complement with CO as a probe of the metal sites. This became particularly necessary in the case of Cu sites which could be not revealed by CO, as shown above. No surface species were formed upon NO admission on the pure HT supports (Fig. 4 curves 1). On oxidised Pt/HT catalysts, NO adsorption caused a partial reduction of Pt ions with the consequent formation of small amounts of Pt mononitrosyls (1770 cm ) and nitrites (1250 cm ). Weak amounts of NO chemisorbed on Pt sites ( 1900 cm ) were also observed (Fig. 4a curve 2). After reduction in H2, linear, bent and bridged Pt nitrosyls (1780, 1700, 1595 cm, respectively, [13]) were formed in high amounts (Fig. 4b curve 2). Conversely, on oxidised Cu/HT samples NO was mainly chemisorbed on Cu sites (band at 1855 cm with a shoulder at 1885 cm ), while only a small fraction of copper was reduced by NO, giving then Cu (NO) species (1747 cm ), nitrites (1250 cm ) and small amounts of nitrates (1600-1300 cm ) (Fig. 4a curve 4). The formation of nitrites has been suggested to involve the reduction of Cu to Cu, as in eqn. (1) [14]. The nitrites thus formed are strongly co-ordinated on Cu sites, which therefore are not able to give nitrosyl species. 

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