Nitric oxide ligand substitution

Oxidation of [Fe(phen)3] + by concentrated nitric acid is autocatalytic. " T e hen)3] + reacts with bromate by rate-determining oxidation at high bromate concentration, [Fe(bipy)3] + and ligand-substituted [Fe(phen)3] + cations react with perbromate by rate-limiting dissocia-587 Reactions of [Fe(diimine)3] + with peroxodiphosphate also involve rate-limiting dissocia-... 

Reactions of the coordinated j8-diketonate ligand are those typical of aromatic ring systems176 with electrophilic substitution at the y carbon being favoured, e.g. reaction with nitric oxide.177... 

As part of the work on model heme FeNO complexes, mechanistic studies on the reversible binding of nitric oxide to metmyoglobin and water soluble Fe, Co and Fe porphyrin complexes in aqueous solution, ligand-promoted rapid NO or NO2 dissociation from Fe porphyrins, reductive nitrosylation of water-soluble iron porphyrins, activation of nitrite ions to carry out O-atom transfer by Fe porphyrins, demonstration of the role of scission of the proximal histidine-iron bond in the activation of soluble guanylyl cyclase through metalloporphyrin substitution studies, reactions of peroxynitrite with iron porphyrins, and the first observation of photoinduced nitrosyl linkage isomers of FeNO heme complexes have been reported. 

Both mono and dinitrosyl cations may be prepared. Salts of the tetrahedral dinitrosyl cation can be prepared either from rhodium nitrosyls (equation 56) or by addition of nitric oxide to ionic rhodium(I) complexes (equation 57). Both nitrosyl groups in complex (47) are bent. The action of dppe upon the i)A(triphenylphosphine) complex produces N2O. Penta- and hexacoordinate mononitrosyl cations are more common and are usually prepared by the action of NOPFe or NOBF4 on rhodium(I) complexes in organonitrile solvents (equation 58). The principal reactions of the complexes are substitutions of the nitrile ligands (equations 59-61). A noteworthy feature of (48), [Rh(NO)(MeCN)3(PPh3)2]+, is that the MeCN ligand trans to the bent nitrosyl group is said to be bent. 

Nitrous oxide, N2O, is commonly used as a mild dental anesthetic and propellant for aerosols on atmospheric decomposition, it yields its innocuous parent gases and is therefore an environmentally acceptable substitute for chlorofluorocarbons. On the other hand, N2O contributes to the greenhouse effect and is increasing in the atmosphere. Nitric oxide, NO, is an effective coordinating ligand its function in this context is discussed in Chapter 13. It also has many biological functions, discussed in Chapter 16. 

The catalytic implications of the alternative coordination modes of nitric oxide in transition metal complexes were first noted by Collman (12). He argued that the linear bent transformation, concomitant with a change in the formal oxidation state of nitrogen from (III) to (I), results in the withdrawal of electron density from the metal center and facilitates the coordination of another ligand into a vacant site. Thus, the mixed carbonyl nitrosyl complex [Co(CO)3(NO)] undergoes thermal CO substitution by an associative mechanism, whereas the iso-electronic, homoleptic carbonyl [Ni(CO)4] reacts by a dissociative pathway (13). 

The substitution of an appropriate number of nitric oxide ligands for carbon monoxide is one possible method of activating metal carbonyl clusters for homo-... 

A nitric oxide (NO) QD-based sensor was developed via the NO-stimulated ligand substitution of a transition metal complex assodated with CdSe/ZnS QDs [142]. The red-colored tris-(N-(dithiocarboxy) carcosine) iron(III)[Fe(DTCS)3] was linked to ammonium-capped QDs by ionic interaction. As a consequence, the functionalized QDs readed with NO by an ET process, followed by ligand substitution to yield the colorless paramagnetic bis(dithiocarbamato) nitrosyl iron(I) complex as a capping layer. This process triggered the luminescence of the QDs that enabled the detection of NO (Figure 6.11). 

Works CF, Jocher CJ et al (2002) Photochemical nitric oxide piecuisois synthesis, photochemistry, and ligand substitution kinetics of ruthenium salen nitrosyl and ruthenium salophen nitrosyl complexes. Inorg Chem 41 3728-3739... 

Although Ru(III) ammine complexes are known to be very inert low-spin d species which only very slowly undergo substitution reactions, their ability to rapidly and efiectively bind nitric oxide seems to be a rather unusual behavior (92). Common characteristics of the Ru(III) nitrosyl complexes, formally Ru NO, studied to date are their octahedral stereochemistry and the presence of an extremely stable Ru—NO mode (93). A broad array of available kinetic and electrochemical data dealing with the formation of Ru(III) nitrosyls clearly shows that the mechanism of unusual fast coordination of nitric oxide to the Ru(III) ammine center cannot be accounted for in terms of a classical ligand substitution process. In this context, the fundamental kinetics of the fast reactions between [Ru (NH3)5X] pC = Cl, ... 

NH3, H2O) and nitric oxide, which all result in the formation of the [Ru (NHslsNO ] product, were reinvestigated in acidic aqueous medium in order to clarify the underlying reaction mechanism (94). As expected, the second-order rate constants obtained in this study for the substitution of various X in [Ru (NH3)5X] by nitric oxide are all much higher than those found for the substitution reactions involving other entering ligands. Importantly, the substitution of Cl by NO is approximately as fast as the displacement of NH3 (0.75 0.03 and 0.3 0.01 s, respectively), but both reactions are much slower than... 

Substitution and oxidation can often both be involved in reactions of tris(diimine)-iron(II) complexes with oxidizing agents. Thus, for example, reaction with hydrogen peroxide involves rate-determining dissociation as the first step. Similarly, initial dissociation seems to be the first step in the predominant pathway for superoxide oxidation of the [Fe(phen)3] cation. Dissociation may also be involved in reactions of diimine-iron(II) complexes with nitrous acid. Here and elsewhere it is recognized that these complexes react with nitric acid—in the initial stages aquation may be the only important path, but autocatalytic redox processes usually become dominant before aquation is complete, especially for the more easily oxidizable ligands and complexes. ... 

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