Ruthenocene oxidation

Isomer shift and quadmpole splitting of salts, [Ru(C5H5)X] Y (X = Cl, Br Y = PFg and X = I, Y = I3) are larger compared to those of ruthenocene. This indicates direct chemical bonding between Ru and Cl, Br and I and that the Ru ion in each salt is in an oxidation state higher than Ru(II) in ruthenocene... 

Various oxidation and reduction reactions of substituted metallocenes have already been discussed. A large number of substituted metallocenes have been oxidized chronopotentiometrically at a platinum foil in acetonitrile solution (39, 46). Electron-withdrawing substituents decrease the ease of oxidation, while electron-donating substituents increase the ease of oxidation with respect to the parent metallocenes. A plot of chronopotentiometric quarter-wave potentials, El, vs. Hammett para-sigma constants shows a definite linear relationship. The Ei s for ruthenocene and osmocene indicate these metallocenes are more difficultly oxidized than ferrocene, in agreement with earlier qualitative observations (18). 

Ferrocene is only one of a large number of compounds of transition metals with the cyclopentadienyl anion. Other metals that form sandwich-type structures similar to ferrocene include nickel, titanium, cobalt, ruthenium, zirconium, and osmium. The stability of metallocenes varies greatly with the metal and its oxidation state ferrocene, ruthenocene, and osmocene are particularly stable because in each the metal achieves the electronic configuration of an inert gas. Almost the ultimate in resistance to oxidative attack is reached in (C5H5)2Co , cobalticinium ion, which can be recovered from boiling aqua regia (a mixture of concentrated nitric and hydrochloric acids named for its ability to dissolve platinum and gold). In cobalticinium ion, the metal has the 18 outer-shell electrons characteristic of krypton. 

Relevant examples are the different actions of the CF3SO3H superacid on dodecamethyl-ruthenocene in inert atmosphere and in the presence of air83. Another example is the oxidation of methane with oxygen in concentrated sulfuric acid in the presence of Pt catalysts to form methanol derivatives84. 

In substituted metallocenes, however, oxidation potentials do not always correlate well with gas-phase ionization energies. For example, although there is a positive trend between the irreversible oxidation potentials of a series of substituted ruthenocenes and their gas-phase energies of ionization, the quantitative correlation between the two is poor (Fig. 18).161 The weak correlation is believed to reflect changes in solvation that accompany the addition of substituents. 

Fig. 18. Ionization energies and oxidation potentials for substituted ruthenocenes.161 TTFMOSi = C5(CF,)4OSiEt3 TTFMH = C5(CF,)4H.

Most decaphenylmetailocenes also exhibit an unsurpassed thermal stability for sandwich complexes. The decaphenyl Ge, Sn, and Pb derivatives do not decompose until above 350°C (under nitrogen) (39), in contrast with around 100°C for the decabenzyl analogs (106). For sym-penta- and decaphenylferrocene and -ruthenocene an extraordinary degree of thermal and oxidative stability is noted (40) they are unchanged in air ( ) at 315°C and volatilize only at 250-300° C in the mass spectrometer. 

When one iron atom in biferrocene is replaced by ruthenium, the second oxidation moves to a more positive potential (by - -400 mV), reflecting the greater difliculty in oxidizing ruthenocene (22). A similar effect is observed in the mixed-metal metallocenophane 4, (M = Fe, M = Ru) the more positive wave (peak potential pk - 0. 94 V) is due to an irreversible two-electron process presumably localized on the ruthenocene unit. Interestingly, [l.l]-ruthenocenophane 4 (M = M = Ru) oxidizes in a chemically reversible two-electron step ( = 0.38 V) to a persistent dication (25). 

Figure 7-26 shows the cyclic voltammetric behavior of ferrocenylruthenocene 1 in acetonitrile solution [89]. It undergoes an initial, reversible, one-electron oxidation at a potential that is almost coincident with that of ferrocene, followed by two closely spaced, one-electron steps, with features of transient chemical reversibility. If one considers that ruthenocene undergoes an irreversible, single-step two electron oxidation, it appears that conjugation with ferrocene tends to stabilize the ruthenocenium cation fragments. This could be attributed to the steric hindrance afforded by the ferrocenyl fragment, which prevents rapid dimerization (followed by... 

Complex Ferrocene-centered oxidation E° V Ruthenocene-centered oxidation Solvent Reference... 

The Cp Ru(ii) fragment, easily available as the tris(acetonitrile) complex salt [Cp Ru(NCMe)3]CF3S03, has been reported as a very well suited building block for the formation of cationic mixed Cp -arene donor systems [73], This constitutes an alternative to ruthenocene derivatives that do not afford the corresponding ruthenocenium salts on oxidation, but usually readily decompose [74]. Since the Cp Ru(ii) fragment has a high affinity for arenes, a number of mono-, di-, and... 

For a discussion of the different chemical and redox properties of decamethylferrocene, -ruthenocene, and -osmocene, and their oxidized forms, see D. O Hare, J. C. Green, T. P. Chadwick, J. S. Miller, Organometallics 1988, 7, 1335 — 1342, and references quoted therein. 

Ruthenium, the homologue of iron in this group, was also shown to form complexes quite early. Ruthenocene, Ru( 5H5)2, is obtained by treatment of the acetylacetonate of tervalent ruthenium with five times the theoretical quantity of the Grignard reagent (206), or, better, by the action of cyclopentadienyl sodium on ruthenium trichloride in tetrahydrofuran (47). It forms pale yellow scales which sublime at 120° and melt at 200°. Its properties are closely similar to those of ferrocene it is soluble in organic solvents, and in the absence of air is not attacked by bases or by sulfuric or hydrochloric acid. Oxidation converts it into the pale yellow [Ru( 5H6)2] + ion. 

The oxidation of ruthenocene, [RuCp2], is not straightforward. On a mercury electrode it is a relatively reversible one-electron step, forming [Hg RuCp2 2]2 + (457) which can be isolated by CPE or via [Hg(CN)2] oxidation in HBF4 solution (458, 459). By constrast, an irreversible two-electron oxidation occurs at platinum at about 0.7 V. Although the process... 

In basic molten salts, the oxidation of [RuCp2] at carbon is highly irreversible, but in a neutral melt (1 1 A1C13 n-butylpyridinium chloride) it behaves more like a quasi-reversible one-electron process. Under acid conditions (excess A1C13), waves are seen at 0.76 and 0.93 V, suggesting stabilization of the ruthenocene dication (462). 

Photo-oxidation of ferrocene by CCI4 in solution can normally only be effected by u.v. irradiation. However it has been observed that the reaction may be carried out with visible light in cetyltrimethylammonium chloride micelles, albeit with low quantum yield.It is suggested that the main effect of micellization may be an increase in the oxidation potential of ferrocene or alternatively that a CTTS state of ferrocene is involved under these conditions. The ring substitution of ruthenocene by irradiation in 1 1 (v/v) solutions of ethanol with CCI4, CHCI3, or CH2CI2 proceeds by a mechanism similar to that previously found for ferrocene. Other reports consider the synthesis of ferrocenyl thioesters and the photooxidation of ferrocene. ... 

Polymers 31 and 34 (as well as co-polymers bearing both ferrocene and ruthenocene moieties) have been partially oxidized with iodine, resulting in weakly semiconducting materials. These materials have also been deposited on electrode surfaces where the polymers act as electrode mediator coatings that aid electron transfer between the electrode and redox-active species in solution. ... 

The d oxidative addition may seem unfamiliar because there are many more examples 47) of d d and d d processes. However, ruthenocene, which is sl (P ruthenium (II) complex with a delocalized electronic structure, undergoes two-electron oxidative addition by I2 and Br2 to give the Ru(IV) complexes Ru(cp)2r and Ru(cp)2Br (48). X-ray studies of Ru(cp)2r show that it is eflFectively a seven-co-ordinate complex (48). 

Ferrocene has also been incorporated in zeolite hosts [244, 255] and hydrocarbon loss on heating and oxidation to ferricinium cation were observed. Similarly, substituted ruthenocenes were also investigated [256, 257]. The ring opening polymerization of a [l]silaferrocenophane within the channels of mesoporous silica (MCM-41) gave precursors of magnetic iron nanostructures [257a,b]. 

Intercalation into lamellar metal oxides and oxide chlorides has also received some attention [353, 354] in particular because of the capacity to intercalate ferrocene. Thus, FeOCl intercalation complexes with ferrocene [355-357] and substituted ferrocenes [358, 359], chromocene [355], cobaltocene [355, 360], ruthenocene [358], and intercalation host-guest complexes of cobaltocene into TiOCl and VOCl [361] have been described and investigated in some detail. Intercalation of some organo-tin compounds into FeOCl has also been reported [362]. 

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