Ru and Os

A variety of [RuH(cod)L ] complexes (L = phosphorus donor) undergo irreversible conversion on heating to the En -cyclooctenyl)RuL ] derivative, the ease increasing with the 

CMe )(BPh.) characterized crystallographically as having trans-hydrazone ligands. 

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A few illustrative examples are the following. Photohydrogenation of acetylene and ethylene occurs on irradiation of Ti02 exposed to the gases, but only if TiOH surface groups are present as a source of hydrogen [319]. The pho-toinduced conversion of CO2 to CH4 in the presence of Ru and Os colloids has been reported [320]. Platinized Ti02 powder shows, in the presence of water, photochemical oxidation of hydrocarbons [321,322]. Some of the postulated reactions are ... 

The residue, which contains Ir, Ru, and Os, is fused with sodium peroxide at 500°C, forming soluble sodium mthenate and sodium osmate. Reaction of these salts with chlorine produces volatile tetroxides, which are separated from the reaction medium by distillation and absorbed into hydrochloric acid. The osmium can then be separated from the mthenium by boiling the chloride solution with nitric acid. Osmium forms volatile osmium tetroxide mthenium remains in solution. Ruthenium and osmium can thus be separately purified and reduced to give the metals. 

Ru and Os, along with Ir, are regarded as the minor platinum metals, being obtained largely as byproducts in the production of Pt, Pd and Rh, and their annual world production is only of the order of tonnes. (Weights of Ru and Os, as of most precious metals, are generally quoted in troy ounces 1 troy ounce = 1.097 avoirdupois ounce = 31.103 g.)... 

Table 25.1 summarizes some of the important properties of Fe, Ru and Os. The two heavier elements in particular have several naturally occurring isotopes, and difficulties in obtaining calibrated measurements of their... 

Figure 25.2 Plot of volt-equivalent against oxidation state for Fe, Ru and Os in acidic aqueous solution.

The most interesting oxides of Ru and Os, however, are the volatile, yellow tetroxides, RUO4 (mp 25°C, bp 130°C< 3>) and OSO4 (mp 40°C, bp 130°C). They are tetrahedral molecules and the latter is perhaps the best-known compound of osmium. It is produced by aerial oxidation of the heated metal or by oxidizing other compounds of osmium with... 

By heating the metal with appropriate oxides or carbonates of alkali or alkaline earth metals, a number of mixed oxides of Ru and Os have been made. They include NasOs Og, LifiOs Og and the ruthenites , M Ru 03, in all of which the metal is situated in octahedral sites of an oxide lattice. Ru (octahedral) has now also been established by Ru Mdssbauer spectroscopy as a common stable oxidation state in mixed oxides such as Na3Ru 04, Na4Ru2 07, and the ordered perovskite-type phases M Ln Ru Og. 

Figure 2S J Teiramenc pentafluondes of Ru and Os, Their structures are similar to, but more disloned than, those of the pentafloorides of F4b and Ta (see Fig. 22 4)...

Fluorides and 0x0 compounds of Ru and Os have already been mentioned, and salts such as (R4N)[Ru04l, (R = n-propyl, n-butyl) are useful reagents to oxidize a variety of organic materials without attacking double or allylic bonds,... 

Fe(CO)s is a highly toxic substance discovered in 1891, the only previously known metal carbonyl being Ni(CO)4. Like its thermally unstable Ru and Os analogues, its structure is trigonal bipyramidal (Fig. 25.10a) but its C nmr spectrum indicates that all 5 carbon atoms are equivalent and this is explained by the molecules fluxional behaviour (p. 914). 

This is also the case in the decamethylmetal-locenes of Ru and Os but not in the iron analogue which has a staggered conformation, presumably due to steric crowding around the smaller metal. 

The structures are shown in Fig. 26.8c and d and differ in that, whereas the Ir compound consists of a tetrahedron of metal atoms held together solely by M-M bonds, the Rh and Co compounds each incorporate 3 bridging carbonyls. A similar difference was noted in the case of the trinuclear carbonyls of Fe, Ru and Os (p. 1104) and can be explained in a similar way. The M4 tetrahedra of Co and Rh are small enough to be accommodated in an icosahedral array of CO ligands whereas the larger Ir4 tetrahedron forces the adoption of the less dense cube octahedral array of ligands. 

The formation of TMM complex from Group VIII transition metal such as Ir, Ru, and Os from precursors derived from (1) has been reported M.D. Jones, R. D.W. Kemmitt,/. Chem. Soc., Chem. Commun., 1985, 811-812. 

Sabatier s Principle is illustrated in Fig. 6.40 where the ammonia rate is plotted for similar conditions versus the type of transition metals supported on graphite. The theory outlined so far readily explains the observed trends metals to the left of the periodic table are perfectly capable of dissociating N2 but the resulting N atoms will be bound very strongly and are therefore less reactive. The metals to the right are unable to dissociate the N2 molecule. This leads to an optimum for metals such as Fe, Ru, and Os. This type of plot is common in catalysis and is usually referred to as a volcano plot. 

Fig. 7.56 Comparison of isomer shift results for compounds of Ru and Os. The velocity scales are chosen such that isoelectronic compounds of the two elements lie nearly on horizontal lines (from [258, 265])...

From Carbyne Complexes. Addition of HC1 across the metal-carbon triple bonds of Ru and Os d8 arylcarbyne complexes yield stable, neutral secondary alkylidene complexes ... 

Specific routes to Ru and Os carbyne complexes will now be detailed. 

Infrared absorptions in the 1300-1400 cm-1 region are observed for all the Ru and Os aryl carbyne complexes. It is likely that these absorptions correspond to combinations of metal-carbon and phenyl ring modes. Additional IR absorptions in the 1550-1600 cm-1 region are also observed for these complexes. 

Carbonyl absorptions in the neutral, five-coordinate Ru and Os carbynes occur at unusually low wavenumbers, suggesting that it is appropriate to regard these molecules as zerovalent complexes. A significant increase in v(CO) for the d8 dicarbonyl cations is noted. IR data for selected carbyne complexes are given in Table IX. 

The similarity between the bonding models for transition metal carbene and carbyne complexes was noted in Section II. That the reactivity of the metal-carbon double and triple bonds in isoelectronic carbene and carbyne complexes should be comparable, then, is not surprising. In this section, the familiar relationship between metal-carbon bond reactivity and metal electron density is examined for Ru and Os carbyne complexes. 

That the neutral d6 Ru and Os carbyne complexes have proved to be unreactive towards nucleophilic reagents suggests the relative electron richness of the MX3(PPh3)2 (M = Ru, Os) fragments when compared with the M(CO)4X residues in the Fischer complexes. The cationic Ru(II) and Os(II) compounds, however, are readily attacked by appropriate nucleophiles, e.g.,... 

The most electrophilic site in the cationic dH Ru and Os arylcarbyne complexes is not the carbyne carbon, but the para position of the aryl ring. As noted in Section II, B,2, hydride reduction of these compounds affords zero-valent vinylidene species ... 

The rate constant for aquation of the 4,4-dithiodipyridine complex [Ru(NH3)5(dtdp)]2+, = 4.5x10 5s is almost exactly the same as that for [Ru(NH3)5(py)]2+, and only slightly slower than that for dissociation of [Ru(CN)5(dtdp)]2+ in aqueous DMSO. Dissociation of [Ru(CN)5 (dtdp)]2+ is, unusually, only 10 times slower than that of its iron(II) analogue [Fe(CN)5(dtdp)]2+ (159). Rate constants for formation and dissociation of [(H3N)5Ru(NCpy)Fe(CN)5] were given and referenced in Table IV (Section II.D.5) a useful summary of rate constants for formation and dissociation of pentacyanoruthenates (D mechanism in all cases) forms part of a review of pentacyanometallates(II) [M(CN)5L]", M = Fe, Ru, and Os (134). 

Bianchini and coworkers [126] found a difference in the chemoselectivity between the metals Fe, Ru, and Os in the complexes [M(H2)H(P(CH2CH2PPh2)3)]-BPh4 in the hydrogenation of benzylideneacetone by transfer from iso-propanol. The Fe and Ru catalysts reduced the 0=0 bond to give the allyl alcohol, with Ru more active than iron (TOF 79 IT1 at 60°C for Ru versus 13 IT1 at 80°C for Fe), while the Os catalyst first reduced the 0=0 bond but then catalyzed isomerization of the allyl alcohol to give the saturated ketone (TOF 55 IT1 at 80°C). The difference in reactivity was attributed to the weak binding of the alkene of the allyl alcohol to Fe and Ru relative to Os in these complexes. A variety of selec-tivities was noted for other unsaturated ketones, whereas unsaturated aldehydes were not hydrogenated. 

The platinum electrode and LSM s were modified with Ru and Os polymers respectively as described in the experimental section. Each sample was rinsed with acetone and placed in an acetonitrile/0.1M TBAP solution and a... 

The reactions of metal bpy ions with oxygen have been studied (193). The bis(bpy) complex ions, [M(bpy)2]2+, of Cr, Ru, and Os formed the dioxygen adducts, whereas the similar complex ions of Mn, Fe, Co, Ni, and Cu were unreactive. The CID of the [M(bpy)202]2+ ions exhibit interesting differences. 

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