Ruthenium tetravalent complexes

Although both the brown [Os(NH3)6] and the yellow [Os(NH3)6]Br have been claimed as products of the reaction of [Os(NH3)6]Br3 with potassium in liquid ammonia,54 the products were not well characterized and could be hydrido ammines or mixtures. There is evidence from the polarographic reduction of [Os(NH3)6]3+ for the existence of [Os(NH3)6]2+ but it appears to be labile to substitution and has not been isolated 55 in this respect osmium differs significantly from ruthenium, for [Ru(NH3)6]2+ is isolable and is in fact a useful synthetic precursor. The tetravalent complex [Os(NH3)s]4+ has also been detected electrochemically, by cyclic voltammetric oxidation of [Os(NH3)6]3+ 55 in acidic solution however, the first product of one-electron oxidation of [Os(NH3)s]3+ is probably [Os(NH3)s(NH2)]3+.ss... 

Physical properties of binary or ternary Ru/Ir based mixed oxides with valve metal additions is still a field which deserves further research. The complexity of this matter has been demonstrated by Triggs [49] on (Ru,Ti)Ox who has shown, using XPS and other techniques (UPS, Mossbauer, Absorption, Conductivity), that Ru in TiOz (Ti rich phase) adopts different valence states depending on the environment. Possible donors or acceptors are compensated by Ru in the respective valence state. Trivalent donors are compensated by Ru5+, pentavalent acceptors will be compensated by Ru3+ or even Ru2+. In pure TiOz ruthenium adopts the tetravalent state. The surface composition of the titanium rich phase (2% Ru) was found to be identical to the nominal composition. 

In 2001, Oi et al. [54] reported on the ruthenium(II) phosphine catalyzed re-gioselective arylation of 2-arylpyridines using aryl halides (Eq. 29). C-C bond formation occurs predominantly at the position ortho to the pyridyl group. The same catalyst system is also effective for the arylation of aromatic imines (Eq. 30) [55]. Although the reaction mechanism has not been elucidated, it was proposed that a tetravalent arylruthenium complex,for example,Ru(Ph)(Br)(Cl)2(I) ,reacts electrophilically with the arylimines. Therefore, C-H bond cleavage is believed to proceed via an electrophilic substitution pathway. 

A new class of binuclear nitrido complexes of tetravalent osmium and ruthenium is described in which the metal atoms are symmetrically bridged by a nitride ligand to give a linear M-N—M unit They have the stoichiometries M2NX8(H20)2]3 and [M2N(NH3)8Y2]3+ (M = Os, Ru X = Cl, Br Y = Cl, Br, etc.). Studies are reported on their vibrational spectra, structures, and bonding. Preliminary studies are reported also on trinuclear complexes of osmium and iridium. Finally, the use of vibrational spectroscopy in the study of metal-nitrido and metal-oxo complexes is discussed briefly. 

From the above discussion it follows that tetravalent and hexavalent thorium, uranium, and plutonium can be separated from the trivalent rare-earth fission products by taking advantage of differences in complexing properties. More highly charged cation fission products, such as tetravalent cerium and the fifth-period transition elements zirconium, niobium, molybdenum, technetium, and ruthenium, complex more easily than the trivalent rare-earths and are more difficult to separate from uranium and plutonium by processes involving complex formation. 

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