Ruthenium complexes nitrogen donors

Let us now examine sample sets of data. We shall consider two reactions, the formation of a biradical1 [Eq. (7-10)] and an electron transfer reaction between two ruthenium complexes [Eq. (7-11)], in which LN represent nitrogen-donor ligands specified in the original reference.2 The chemical equations are... 

In the transition metal-catalyzed reactions described above, the addition of a small quantity of base dramatically increases the reaction rate [17-21]. A more elegant approach is to include a basic site into the catalysts, as is depicted in Scheme 20.13. Noyori and others proposed a mechanism for reactions catalyzed with these 16-electron ruthenium complexes (30) that involves a six-membered transition state (31) [48-50]. The basic nitrogen atom of the ligand abstracts the hydroxyl proton from the hydrogen donor (16) and, in a concerted manner, a hydride shift takes place from the a-position of the alcohol to ruthenium (a), re-... 

Since the early 1980s rich thermal and photochemical redox chemistries of Os =N species containing nonlabile oxidation-resistant nitrogen donor ligands have emerged. However, there are only a few examples of ruthenium(VI) nitrido complexes of this type, and their redox chemistry is largely unexplored. 

Extensive work on cis- and trans-d o o complexes of ruthenium(VI) and osmium(VI) containing nonlabile, oxidation-resistant nitrogen donor ligands has been reported. 

A tridentate (r 6 ri1 r 1) strapped arene complex of ruthenium(II), 20, containing a pair of auxiliary nitrogen donor atoms derived from (R, R)-1,2-diphenylethylenedi-amine, has been prepared by a sequence in which the functionalized arene is first coordinated to ruthenium(II), as shown in Scheme 5.25 The structure of 20 has been... 

The electrochemical behavior of ruthenium(IV) oxo complexes of tertiary amine has also been extensively studied. For the [RuIV (L)(0)(OH2)]2+/[Rura(L)(OH)(OH2)]2+ couples, the ring size of the macrocycle L has very little effect on E°. However, replacement of a tertiary nitrogen donor by a pyridyl group leads to an increase in E°. 

We have already alluded to the diversity of oxidation states, the dominance of oxo chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of m-hydroxylation, hydroxyamination or animation of alkenes, see p. 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

The complex [Ru(EDTA)(H20)] undergoes substitution reactions with several ligands, replacing the water molecule with the ligand. In all cases the ruthenium stays in the +3 oxidation state and the ligands use a nitrogen donor atom to bind to the metaL... 

Ruthenium(IV), d, forms a more limited number of complexes involving mainly the halides (except the iodide), oxalate, and sulfate, together with r-acceptor nitrogen donor ligands. RUO2 is used as a catalyst and as an electrode material. 

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