Nitrosonium complexes ligands

Nitrosonium complexes 20a-d of l-R-2-methylacenaphthylenes 21a-d (Scheme 15) can be considered as complexes with two-electron ligands, as unlike complexes of other polycyclic aromatic compounds (8, 52), nitrosonium... 

The NO ligand can be supplied by nitric oxide itself, but there are many other sources such as nitrite, nitrate or nitric acid, nitrosonium salts or N-methyl-7V-nitrosotoluene-p-sulphonamide (MNTS). The introduction of a nitrosyl group into a ruthenium complex is an ever-present possibility. 

The most important physiological nitrogen substrate of peroxidases is undoubtedly nitric oxide. In 1996, Ishiropoulos et al. [252] suggested that nitric oxide is able to interact with HRP Compounds I and II. Glover et al. [253] measured the rate constants for the reactions of NO with HRP Compounds I and II (Table 22.2) and proposed that these reactions may occur in in vivo inflammatory processes. The interaction of NO with peroxidases may proceed by two ways through the NO one-electron oxidation or the formation of peroxidase NO complexes. One-electron oxidation of nitric oxide will yield nitrosonium cation NO+ [253,254], which is extremely unstable and rapidly hydrolyzed to nitrite. On the other hand, in the presence of high concentrations of nitric oxide and the competitor ligand Cl, the formation of peroxidase NO complexes becomes more favorable. It has been shown [255]... 

Neutral (cyclobutadiene)Fe(CO)3 complexes undergo thermal and photochemical ligand substitution with phosphines, with alkenes such as dimethyl fumarate and dimethyl maleate and with the nitrosonium cation to generate the corresponding (cyclobutadiene)Fe(CO)2L complexes15. These types of complexes are presumably intermediates in the reaction of (cyclobutadiene)Fe(CO)3 complexes with perfluorinated alkenes and alkynes to generate the insertion products 266 or 267 respectively (Scheme 70)15,238. 

In Sect. 5.2, the strong 7r-donor ability of methoxide and fluoride has been elaborated. These two ligands effect a push-pull effect on the nitrosonium ion bound in Os(OEP)NO(OMe) [31c] and Os(OEP)NO(F) [3Id], as indicated by the low NO-stretching frequencies of the NO ion as compared with the dinitrosyl Os(OEP)(NO)2 [31e] and the perchlorato complex, 0s(0EP)N0(0C103) ([3If], Table 11). Thus, the a/7r-donor balance for the coordinated anions decreases in the series OMe > F > NO > OClOf. [31c] and [3Id] can be vaporized at 200°C/10-6 Torr in a mass spectrometer, while the dinitrosyl [31e] decomposes above 100 °C. This demonstrates the push-pull effect also in a chemical sense. 

Here again measurements are confined to the nitrosyl pentacyanides. There is a large literature on the ESR spectrum of K3[Cr(NO)(CN)5] 48, 68, 71 and references therein) and some disagreement as to the interpretation, but the formulation of the complex as a nitrosonium coordination compound is upheld by the results, and this is also the conclusion reached from ESR studies on the isoelectronic complex K2[Mn(NO)(CN)5] 68). In the case of [Fe(NO)(CN)s], a species not yet isolated from solution, the delocalization of the unpaired electron onto the ligand appears to be such that the complex may almost be regarded as an example of nitric oxide donating an electron pair only to iron(II) 45). A study of C hyperfine interaction in the ion has recently been made 15). 

The compound Tr-CsHsNiNO is regarded as formed by a three-electron donation from the nitric oxide ligand. Most NO complexes are best considered as being formed by an initial one-electron transfer to the metal prior to donation from the nitrosonium ion (NO ). The nitric oxide ligand, a so-called odd molecule, is then effectively a three-electron donor. Such a bonding mode is supported by considerable infrared, ESR, and other structural data. It should be noted, however, that recent interpretation of ESR data in terms of MOT indicates that the nitric oxide ligand also can be described by the formal structures NO- and NO , in some complexes. 

A 1 1 cage complex of the ligand 822 (Scheme 5.37) with encapsulated nitrosonium cation has been described in [35] to be a mild nitrosa-tion agent for secondary amides RCONHR this agent selectively reacts with A-methylated amides only due to the steric hindrances between more bulky alkyl substiments of analogous alkylamide... 

Haim and Taube reacted [CoN3(NH3)s]2+ with nitrosyl chloride in water S which led to the formation of [Co(NH3)5(H20)]3+, dinitrogen, and nitrous oxide. [Co(N3)Cl(en)2]+ underwent a similar reaction in water56 57 with formation of [CoCl(en)2(H20)]2+. Following this early work, several methods were developed that similarly employed azide ligand elimination as the result of redox transformations in non-aqueous solvents. The complex [CoN3(NH3)s]2+ and nitrosonium salts were reacted in trimethylphosphate, tetramethylene sulfone,59 or organonitriles with the formation of the... 

In order to prepare a homoleptic solvento-complex by metal oxidation in a non-aqueous medium, the reduction products must not compete with the solvent molecules as ligands. Nitrosonium perchlorate, N(DC104, is a suitable oxidant. 4,15 Reactions have been performed in acetonitrile, nitromethane and ethylacetate. In acetonitrile this oxidant converts copper powder into the copper(I) and copper(II) homoleptic solvento-complexes, [Cu(MeCN)4][C104] and [Cu(MeCN)4][C104]2. On boiling an acetonitrile solution of these complexes with metallic copper, reduction of the copper(II)... 

In didiloromethane reaction of the ruthenium thiolate complex, [Ru(SPh)(CD)2(il5-Cp)], with one equivalent of the nitrosonium salt, NOPFg, results in oxidation of the thiolate ligand and precipitation of the dimer, [ Ru(CO)2(T 5-Cp) 2(li-HiSSPh)] pF6].39 Oxidation by NO - occurs also in the reaction O between the nickel(II) phosphine complexes, INiX2(PPh3)2] (X = Q, Br, NQ3), and NOQ in a mixture of benzene and cyclohexane. The reactions result in formation of the dimers, NiXQ(OPPh3)]2. 

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