Nitrosyl cation formation

Reactions 14.68 and 14.69 showed the formation of salts containing the [NO] (nitrosyl) cation. Many salts are known and X-ray diffraction data confirm an N—O distance of 106 pm, i.e. less than in NO (115 pm). A molecular orbital treatment of the bonding (seeproblem 14.16 at the end of the chapter) is consistent with this observation. In going from NO to [NO] there is an increase in the NO vibrational frequency (1876 to Rs2300cm ), in keeping with an increase in bond strength. All nitrosyl salts are decomposed by water (equation 14.94). 

Reactions 15.71 and 15.72 showed the formation of salts containing the [NO] (nitrosyl) cation. Many salts are... 

A very complete review of the mechanisms of formation of NDMA, its occurrence and means for mitigating its formation (Mitch 2003), emphasizes the complexity of the situation. Nonetheless, some clear-cut conclusions have been possible. One route to NDMA involves nitrosation, via formation of nitrosyl cation NO" or other reactive nitrogen containing species such as dinitrogen trioxide (N2O3) as a result of acidification of nitrite ... 

A majority of the nitrosyl complexes contain NO (nitrosyl or nitrosonium ion) as the hgand. The nitrosyl cation is isoelectronic with carbon monoxide. Hence, the bonding between nitrogen and metal in nitrosyls is analogous to that of carbon and metal in carbonyls. However, the hgand nitrosyl (NO ) is a three-electron donor, as it donates one electron to the metal ion prior to the donation of an electron pair for the formation of a coordinate covalent bond. 

Diazotization is a complex reaction (Scheme 1). When performed in acidic media with sodium nitrite, NOx or nitrosyl halides, its kinetics are dependent upon the acidity of the medium in media with a Hammett acidity constant (-H0) from — 1 to 3 the reaction rate increases with acidity and the formation of the nitroso cation is the rate-limiting step, in more acidic media (-H0 > 4) the reaction rate decreases when acidity increases and the deprotonation of intermediate 6 is the rate-limiting step.6-9... 

Nitrosonium ion was found to promote iodination of cyclohexene when AcOH was used as solvent, the trans-iodo acetoxy derivative was formed in a good yield. Solvolysis of the latter, followed by saponification, led to a cA-diol so that this method can serve as an alternative to the wet-Prdvost reaction. The NO+ cation is believed to promote the formation of some positive iodine species (equation 1). Oxidation by oxygen leads to the regeneration of iodine and NO+ from nitrosyl chloride189. 

Formation of the N02 complex 36 (Scheme 1) upon addition of NaN02 to [(l)FeBr]Br in methanol is immediate. The product has been fully characterized by IR, NMR, UV/Vis spectroscopies and other methods. Attempts to obtain single crystals of 36, however, revealed a remarkable transformation into the nitrosyl complex (Fe(NO) 7 by slow hydrolysis. Complex 36 is diamagnetic with well-resolved NMR spectra which, similar to the spectra of the carbonyl and (Fe(NO) 6 complexes, indicate a C2V symmetrical cation in solution. The cyclic voltammogram (DMSO solution) has one quasi-reversible one-electron redox wave at —0.07 Vas the only feature, which we assign to the Fen/Fem couple of the mononuclear complex. Addition of water to methanol solutions of 36 (in sub-stoichiometric or stoichiometric amounts) under anaerobic conditions leads to the formation of the... 

Aerobic oxidative cyclization of 2,2-dihydroxystilbenes via oxygen cation radical leading to the formation of c -4b,9b-dihydrobenzofuro[3,2-h]benzofurans was carried out in an enantioselective manner by using (nitrosyl)Ru(salen) as a catalyst under irradiation conditions <02CL36>. 

The features of initiation of free radical reactions in polymers by dimers of nitrogen dioxide are considered. The conversion of planar dimers into nitrosyl nitrate in the presence of amide groups of macromolecules has been revealed. Nitrosyl nitrate initiates radical reactions in oxidative primary process of electron transfer with formation of intermediate radical cations and nitric oxide. As a result of subsequent reactions, nitrogen-containing radicals are produced. The dimer conversion has been exhibited by estimation of the oxyaminoxyl radical yield in characteristic reaction of p-benzoquinone with nitrogen dioxide on addition of aromatic polyamide and polyvinylpyrrolidone to reacting system. The isomerisation of planar dimers is efficient in their complexes with amide groups, as confirmed by ab initio calculations. 

The results of the present study are summarized in Table 2. For comparison reasons, the well defined carbonyls and nitrosyls of Rh on US-Ex are also included. As in the case of Rh surface complexes [1-4] US-Ex act as a kind of unique matrix for the formation of well defined surface carbonyls. The following properties of US-Ex might be responsible for these effects the remaining amount of Al atoms as centres for the localization of cationic carbonyl species is small (at a Si Al ratio of ca.lOO only about 2 per unit cell). At the same time, also the amount of other cations (as Na in the case of NaX or NaY) and adsorbed molecular water is rather small in US-Ex. The carbonyls formed in US-Ex are, therefore, isolated from each other and free of interaction with other species in the supercages of the zeolite framework. 

Method b employs acyl chloride, but the quantitative removal of AgCl is very difficult. Method c does not suffer this disadvantage, because the gaseous NOCl can easily be removed from the reaction medium however, the starting material, i.e. the nitrosyl salt, may itself initiate the polymerization (e.g. polymerization of THF)131). Thus, this method cannot be used for the in situ formation of acyl cations, which is a frequent practice. 

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). 

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