Ruthenium dimeric

Imamura (11,20,21) synthesized several similar perpendicular dimers exploiting axial coordination of the 4-pyridyl free-base porphyrin to Ru(II)CO (3) and Os(II)CO (4) porphyrins (Fig. 1). The pyridine-ruthenium and pyridine-osmium interactions are much stronger than the pyridine-zinc interaction, and the complexes are perfectly stable in solution and can be isolated by precipitation. One of the ruthenium dimers was characterized by FAB-MS (11). Complexation is accompanied by characteristic changes in JH NMR chemical shift, indicating... 

One such reaction that has been studied is the electrocatalytic reduction of oxygen directly to water.25,27 The electrocatalysts for this process are often based on metal porphyrins and phthalo-cyanins. Thus a graphite electrode whose surface was modified by the irreversible adsorption of a cofacial dicobalt porphyrin dimer was able to reduce oxygen under conditions where the reduction did not occur on the bare electrode itself. Similarly, a catalytic chemically modified electrode for the oxidation of chloride to chlorine has been prepared28 where the active catalyst was reported to be a ruthenium dimer, [(bipy)2(OH)RulvORuvO(bipy)2]4+, which was reduced to the corresponding [Rum-RuIV] dimer during the reaction. 

These iron and ruthenium dimers are exceedingly robust compounds. Indeed decomposition of trinuclear phosphidoacetylide-bridged clusters invariably yields these molecules as major decomposition products ... 

An electrophilic palladation by a phenyl palladium intermediate at C(3) and a C(3) to C(2) migration of a palladium species, followed by reductive elimination, is indicated. 2-Phenylpyridine has been formed by the reaction of pyridine and iodobenzene at 150 °C in the presence of phosphido-bridged ruthenium dimer complexes.49 A catalytic cycle involving one of the complexes in the system was proposed. Optimum conditions for the efficient and regioselective palladium-catalysed C(2) arylation of ethyl 4-oxazolecarboxylate (47) with iodobenzene have been presented.50... 

The 77-cyclopentadienyliron dicarbonyl dimer and the mixed metal carbonyl 7r-cyclopentadienyliron-manganese heptacarbonyl are protonated by strong acids to form isolatable salts, namely [CpFe(CO)2]2H +PF6 and [CpFeMn(CO)7H]+PF6 . The ruthenium dimer [CpRu(CO)2]2 behaves similarly, although no salt was isolated (63). 

ESCA spectra have been recorded for a series of pyrazine-bridged ruthenium dimers including [(NH3)5Ru(pyz)Ru(NH3)5]s H and [(bipy)2ClRu(pyz)RuCl(bipy)2]3+.50 The data show that both Ru and Ruin are present in those complexes although the metal sites are equivalent. The speed with which ESCA monitors electron distribution (ca. 10"17 s) would seem to make it an excellent spectrosocpic tool for such valence-state assignments. 

Sadowski RC, Engstrom G, Tian H, et al. Use of photoactivated ruthenium dimer complex to measure electron transfer between the Rieske iron-sulfur and cytochrome C in the cytochrome bcx complex. Biochemistry 2000 39 4231-6. 

Cyclopentadienyl dicarbonyl ruthenium dimer 132 reacts with silver tetrafluoroborate and diphenylacetylene to afford the cyclobutadiene ruthenium complex 133 (Scheme 12). Irradiation of 133 in dichloro-methane in the presence of several alkynes leads to the arene cyclopentadienyl ruthenium complexes 125 in high yield. This reaction appears to be a general route to sterically crowded ruthenium arene cations (55). 

There have been only a handful of studies on exchange coupled ruthenium dimers and yet the information available on metal-metal coupling is potentially as valuable as that obtained from mixed-valence complexes. The reason for this lack of activity has been the greater familiarity of researchers with the chemistry of Ru(II) bound to 7r-acid ligands. The synthetic pathways to complexes of this type are well explored (7) and possess the tremendous advantages of stability and ease of handling. Ru(II) complexes that incorporate anionic n donor... 

The first real indication of antiferromagnetic superexchange in ruthenium dimers that possessed polyatomic bridging ligands was found for the complex [ (NH3)5Ru 2(/u-t-BuMN)]5+ (76), where... 

The most intensively studied molecular systems mimicking the action of the WOC are based on the / -oxo-bridged ruthenium dimer [m-(bpy)2Ru(0H2)]20" +, where each ruthenium is associated with two bipyridyl ligands and one water molecule. The catalytic water oxidation cycle involves abstraction of two electrons from each of the Ru(II) centers forming two dioxoruthenium(IV) moieties which convert back to the starting state under oxygen release and subsequent re-aquation of the ruthenium metal centers [119]. 

Ruthenium complexes having cyclopentadienyl ligands have also been extensiveK investigated. Because ruthenocene is relatively unreactive, much attention has been focused on mononuclear ruthenium complexes with one cyclopentadienyl ligand or ruthenium dimers having cyclopentadienyl ligands. 

All manipulations must be carried out in an inert atmosphere using degassed solvents.9 To a 25-mL, round-bottom flask fitted with a nitrogen inlet, reflux condenser, and magnetic stirring bar is added the di-chloro(rj6-hexamethyl-benzene)ruthenium dimer (0.2 g, 0.3 mmole). Under a counterstream of ethylene, anhydrous sodium carbonate (0.2 g) and ethanol (15 mL) are added. The mixture is stirred and heated under reflux under a slow flow of ethylene for 2 hours the solution initially turns deep red and finally becomes brown. After cooling to room temperature, solvent is stripped in vacuo and the residue is extracted with four 5 mL portions of hexane. The filtered extract is concen-... 

The interplanar separation of Rh(OEP)In(OEP) is 3.41 A compared to 3.26 A for [Ru(OEP)]2 As is also observed for the ruthenium dimer the In(OEP) core is twisted 21.8° relative to the Rh(OEP) group. Both the indium and rhodium atoms have an out-of-plane distance A4N which is the same as that previously reported for the corresponding o-bonded metal carbon complexes (given in Table 15 of part B V). A covalent radius of 1.36 A may be estimated from the metal-carbon bond length in In(TPP)(CH3). Similarly the covalent radius of the rhodium atom in Rh(OEP)(CH3) is equal to 1.26 A, giving a predicted covalent Rh-In distance of 2.62 A. This latter value is in good agreement with the observed value (2.584(2) A). In addition, the reactivity of the dimer... 

Figure 4 Resonance Raman spectra of the ruthenium dimer in various oxidation states numbers in parentheses indicate the oxidation states on the ruthenium ions of the dimer (adapted from ref. 13).

---