Ruthenium complexes nitrosyls

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. 

Besides ruthenium porphyrins (vide supra), several other ruthenium complexes were used as catalysts for asymmetric epoxidation and showed unique features 114,115 though enantioselectivity is moderate, some reactions are stereospecific and treats-olefins are better substrates for the epoxidation than are m-olcfins (Scheme 20).115 Epoxidation of conjugated olefins with the Ru (salen) (37) as catalyst was also found to proceed stereospecifically, with high enantioselectivity under photo-irradiation, irrespective of the olefmic substitution pattern (Scheme 21).116-118 Complex (37) itself is coordinatively saturated and catalytically inactive, but photo-irradiation promotes the dissociation of the apical nitrosyl ligand and makes the complex catalytically active. The wide scope of this epoxidation has been attributed to the unique structure of (37). Its salen ligand adopts a deeply folded and distorted conformation that allows the approach of an olefin of any substitution pattern to the intermediary oxo-Ru species.118 2,6-Dichloropyridine IV-oxide (DCPO) and tetramethylpyrazine /V. V -dioxide68 (TMPO) are oxidants of choice for this epoxidation. 

None of the ruthenium complexes gave greater than trace amounts of disproportionation. Both of the nitrosyl-containing ruthenium derivatives showed some double-bond isomerization activity with 1-2% 1-pen-tene being observed. 

Tfouni E, Krieger M, McGarvey BR, Franco DW. Structure, chemical and photochemical reactivity and biological activity of some ruthenium amine nitrosyl complexes. Coord Chem Rev 2003 236 57-69. 

Sauaia MG, de Souza Oliveira F,Tedesco AC, Santana a Silva R. Control of NO release by light irradiation from nitrosyl-ruthenium complexes containing polypyridyl ligands. Inorg Chim Acta 2003 355 191-6. 

Miranda KM, Bu X, Lorkovic IM, Ford PC. Synthesis and structural characterization of several ruthenium porphyrin nitrosyl complexes. Inorg Chem 1997 36 4838. 

Modulation of NO release can be induced by one-electron reduction, which occurs at NO to yield coordinated NO, or by photolysis (41,46). Thus, the ruthenium complexes were studied in search for an ideal system for the site-directed NO delivery from thermally stable precursors which can release NO when triggered by light. A large number of [Ru—NO] nitrosyls release NO upon exposure to UV light and their potential as NO donors under the control of light has been surveyed. In general, the... 

Ruthenium salen nitrosyl complexes react catalytically with thiiranes and convert them to olefins and 1,2,3-trithiolanes 163 (Scheme 34) or 1,2,3,4-tetrathianes 164 (Scheme 35) <2001JA4770>. 

The reaction was first-order in the concentration of each reactant and there was no evidence for a reverse reaction step. Entropies of activation for the three reactions were in the range of -110 to -130 J mol" K". The volumes of activation were -13.6 0.3 and -18.0 0.5 cm mol for the substitution of the NH3 and Cl groups, respectively (determination of this parameter for the substitution of H2O was not possible). The authors presented several possible mechanisms for consideration to explain the rapid reactions and the magnitudes of the activation parameters. It was eventually concluded that the most compatible mechanism consistent with the results and product species characterisation was a unique combination of associative ligand binding and concerted electron transfer to yield the stable ruthenium(II) nitrosyl complex. 

Besides this iron-nitrosyl complex, nitrosyl complexes of other transition metals can be used for nitrosation. As discussed by Bottomley et al. (1973, see also review by Bottomley, 1978), these complexes are not only sources of nitrosyl ions (NO" ) as two-electron acceptors, but also of nitroxide (NO ) as one-electron donor. Bottomley found that they are nitrosating reagents only if their NO stretching frequency is greater than 1886 cm The ruthenium nitrosyls are particularly interesting with respect to their reaction with aliphatic and aromatic primary amines. We discuss them in the context of metal dinitrogen complexes (Sect. 3.3). 

In the context of this book, investigations on the reactions of nitrosyl ruthenium complexes with aromatic and aliphatic primary amines are interesting, as they permit conclusions on the relative stabilities of bonds between dinitrogen and Ru aryl... 

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