Hydroxylamine complexes

Examples of the osmium and iridium complexes are Os(PPh3)2Cl(NO) and Ir(PPh3)3(NO), respectively [216]. The osmium compound gave, on reaction with HC1, the first characterized complex with the feature of an N-coordinated HNO, Os(PPh3)2Cl2(HNO), which was confirmed by X-ray crystallography. On the other hand, the nitrosylated iridium compound gave the hydroxylamine complex [216]. 

Fe(CN)4NO]3- ion upon one-electron reduction, followed by a proton-induced disproportionation reaction to regenerate [Fe(CN)4 NO]2-, along with the formation of [Fe(CN)4NH2OH]2-. The overall reaction involves a four-electron reduction of NP to the hydroxylamine complex. 

Nitrosyl complexes have also been synthesized using hydroxylamine. Although the mechanism of this process is not well understood, hydroxylamine complexes are known.92 Therefore it is possible that oxidation or deprotonation of the coordinated NH2OH group could occur, leading to the products obtained in equation (17). 

Because of the asymmetry of hydroxylamines and the fact that they are com-plexed by vanadate in a side-on fashion similar to hydrogen peroxide, they provide details of the chemistry not otherwise easily accessible. Further interest in these compounds arises from both their in vivo and in vitro insulin-mimetic properties. Animal studies have shown that the bis(., ., -dimcthyl)hydroxamidohydroxooxovan-adate is as effective as other insulin-mimetics such as bis(maltolato)oxovana-dium(IV). Unlike the peroxo complexes, the hydroxylamine complexes influence enzyme activity by a nonoxidative mechanism [4,5],... 

Coordination of vanadate by hydroxylamines is similar in many respects to coordination by hydrogen peroxide. Various hydroxylamine complexes are known, although only detailed studies of the aqueous chemistry have been carried out with hydroxylamine and its A -melhyl and A,A-dimcthyl derivatives. -substitution apparently has only a small influence on product formation. There is, however, scope for a wider range of isomeric forms with the A-methylated ligand compared to the unsubstituted and dimethylated ligands, and a number of isomers have been observed... 

Hydroxylamine complexes display internal dynamics that are not generally observable with similar peroxo complexes. There is the possibility of end-for-end rotation of the hydroxylamine group. This rotation gives rise to isomers that, in principle and in practice, are observable. In fact, for the imidazole complexes, dynamics studies have shown there is rapid exchange between the various isomeric complexes that arises from end-for-end rotation of the hydroxylamine groups and from imidazole dissociation and reassociation [2],... 

It seems strange that no hydroxylamine complexes of osmium are established. There is a brief report of a deprotonated complex Os(NO)(NHOH)Cl2(PPh3)2, made from Os(NO)2(PPh3)2 and HC1. The vNO band is at 1860 cm-1.247... 

Reaction mechanism Based on the observation of reaction intermediates in the crystal structure and on quantum chemical calculations Einsle et al. [148] propose an outline of the first detailed reaction mechanism of the cytochrome c Nir from W. succinogenes. Nitrite reduction starts with a het-erolytic cleavage of the weak N-O bond, which is facilitated by a pronounced backbonding interaction between nitrite and the reduced active site iron. The protons come firom a highly conserved histidine and tyrosine. Elimination of one of both amino acids results in a significant reduced activity. Subsequently, two rapid one-electron reductions lead to a FeNO form and, by protonation, to a HNO adduct. A further two-electron two-proton step leads to hydroxylamine. The iron in the hydroxylamine complex is in the Fe(III) state [149], which is unusual compared to synthetic iron-hydroxylamine complexes where the iron is mainly in the Fe(II) state. Finally, it readily loses water to give the product, ammonia. This presumably dissociates firom the Fe(III) form of the active site, whose re-reduction closes the reaction cycle. 

INFRARED ABSORPTION SPECTRA OF HYDROXYLAMINE COMPLEXES OF COBALT, NICKEL AND PLATINUM. 

INFRARED ABSORPTION SPECTRA OF HYDROXYLAMINE COMPLEXES OF COBALT, NICKEL, AND PLATINUM. //ENGLISH TRANSLATION OF ZHUR. NEORG. KHIM. 12/1/ 163-,... 

A range of cations, notably Fe catalyse the reaction and also reduce the ratio N2/N2O in the product. It is claimed that when such cations are completely com-plexed, decomposition does not occur. A mechanism involving decomposition of hydroxylamine complexes of Fe Cu, or Co is preferred. Calorimetric determinations of the heat of solution of a range of alkylhydrazines in water, and in 0.1 mol dm hydrochloric acid, have been correlated in terms of a constants and hydration parameters. This enables calculations of the relative basicities of the two nitrogen atoms in an unsymmetrical alkylhydrazine to be made. This may be of value in interpreting the mechanism of oxidation of the alkylhydrazines. The mechanisms involved in the synthesis of NF4+[AsFj] from NFj, AsFg, and Fg have been discussed, and an alternative mechanism to that suggested earlier has been proposed for the thermal decomposition of NF4+[AsFe]. ... 

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