Ruthenium carbonyl compounds

Various ruthenium carbonyl compounds can be prepared on the surface of Si02 (Scheme 16.2) or on the surface of MgO, AI2O3, ZnO or La203 (Scheme 16.3), as described below. 

Scheme 16.2 Convenient syntheses of ruthenium carbonyl compounds on the surface of Si02.

Scheme 16.3 Convenient syntheses of ruthenium carbonyl compounds on the surface of MgO AI2O3, ZnO, or La203, (the subscript x refers to the pretreatment temperature, in °C).

Caution. Because of the toxicity of carbon monoxide and ruthenium carbonyl compounds, all manipulations should be carried out in an efficient fume hood, wearing gloves and eye protection. 

J. Lewis, and P. R. Raithby, Reflections on Osmium and Ruthenium Carbonyl Compounds, J. Organomet. Chem. 500, Ill-Til (1995). 

The dimer has also been prepared by refluxing Ru3(CO)i2 in halo-carbons such as CCI4, CHCI3, and CHBrg 45, 222, 343). In these reactions the initial product has been shown to be an unidentified chlorocarbon derivative of a ruthenium carbonyl compound 222). The dimer is produced by decomposition of this compound in hot solvents. 

Ruthenium chloride reacts easily with carbon monoxide under pressure to afford ruthenium carbonyl compounds. The product is recrystallized in hexane to yield a yellow crystal in 74% yield. The total yield is 85-95% by using the mother liquors repeatedly [8]. The Ru3(CO)i2 obtained decomposed at its melting point in air, ignites violently and is stable up to 231 °C in argon. It dissolves in most solvents except for petroleum ether and alcohol [8,9]. 

In basic solution Fe(CO)6 and M(CO) (M = Cr, Mo, or W) catalyse the water-gas shift reaction (i.e. HgO + C0 C02 + H2). Ruthenium carbonyl compounds catalyse this reaction in both basic and acidic media mixed ruthenium-iron carbonyl catalysts e.g. [FeRu3H2(CO) 3] are considerably more active in basic solution than either ruthenium or iron carbonyls alone. [PtLg] (activity L = PPr 3>PEt3>PPh3) and KaPtCl4-SnCl4,5H20 also catalyse the water-gas shift reaction the proposed mechanism for the latter catalyst is shown in Scheme 1. ... 

Ruthenium. Cyclic secondary amines, including morpholine and piperidine, can be carbonylated to give iV-formyl derivatives in the presence of ruthenium carbonyl compounds [Ru(OaCMe)(CO)2ln or Ru3(CO)ig. With the former catalyst it is possible to isolate an intermediate [RuCOgCMe)-(amine)(CO)2]OT, where m is probably 2. ... 

Ruthenium carbonyl compounds were found to be suitable catalysts for the hydroformylation of alkenes using CO2 as the source of CO along with H 2. In the multistep process, CO2 is first reduced to CO and then used in situ in hydroformylation. The best results were obtained by using a [Ru(C0)3Cl2]2/Li2C03 system [66]. 

Ruthenium is excellent for hydrogenation of aliphatic carbonyl compounds (92), and it, as well as nickel, is used industrially for conversion of glucose to sorbitol (14,15,29,75,100). Nickel usually requires vigorous conditions unless large amounts of catalyst are used (11,20,27,37,60), or the catalyst is very active, such as W-6 Raney nickel (6). Copper chromite is always used at elevated temperatures and pressures and may be useful if aromatic-ring saturation is to be avoided. Rhodium has given excellent results under mild conditions when other catalysts have failed (4,5,66). It is useful in reduction of aliphatic carbonyls in molecules susceptible to hydrogenolysis. 

The palladium and platinum metals also form carbonyl compounds. Of the expected compounds Pd(CO)4, Pt(CO)4, Ru(CO)5, Os (CO) 5, Mo-(CO)e, and W(CO)6 only Mo(CO)e has been prepared, although some unsaturated ruthenium carbonyls have been prepared. The compounds Pd(CO)2Cl2, Pt(CO)2Cl2, K[PtCOCl3], etc., show the stability of the four dsp2 bonds. It would be interesting to determine whether or not each CO is bonded to two metal atoms in compounds such as [Pt(CO)Cl2]2, whose structure is predicted to be... 

Carbonylation of alkynes is a convenient method to synthesize various carbonyl compounds. Alper et al. found that carbonylation of terminal alkynes could be carried out in aqueous media in the presence of 1 atm CO by a cobalt catalyst, affording 2-butenolide products. This reaction can also be catalyzed by a cobalt complex and a ruthenium complex to give y-keto acids (Scheme 4.8).92... 

Azolides are also capable to acylate anionic metal carbonyl compounds. For instance, disodium tetracarbonylferrate as well as the corresponding ruthenium and osmium compounds can be formylated with formylimidazole in the presence of boric acid methyl ester ... 

Various ruthenium complexes catalyze the isomerization of allylic alcohols to saturated carbonyl compounds. Ru(acac)3 is an effective catalyst for the isomerization of a wide range of allylic alcohols (Scheme 12).35... 

The plausible mechanism of this ruthenium-catalyzed isomerization of allylic alcohols is shown in Scheme 15. This reaction proceeds via dehydrogenation of an allylic alcohol to the corresponding unsaturated carbonyl compound followed by re-addition of the metal hydride to the double bond. This mechanism involves dissociation of one phosphine ligand. Indeed, the replacement of two triphenylphosphines by various bidentate ligands led to a significant decrease in the reactivity.37... 

The ruthenium-, rhodium-, and palladium-catalyzed C-C bond formations involving C-H activation have been reviewed from the reaction types and mechanistic point of view.135-138 The activation of aromatic carbonyl compounds by transition metal catalyst undergoes ortho-alkylation through the carbometallation of unsaturated partner. This method offers an elegant way to activate C-H bond as a nucleophilic partner. The rhodium catalyst 112 has been used for the alkylation of benzophenone by vinyltrimethylsilane, affording the monoalkylated product 110 in 88% yield (Scheme 34). The formation of the dialkylated product is also observed in some cases. The ruthenium catalyst 113 has shown efficiency for such alkylation reactions, and n-methylacetophenone is transformed to the ortho-disubstituted acetophenone 111 in 97% yield without over-alkylation at the methyl substituent. 

This aldol condensation is assumed to proceed via nucleophilic addition of a ruthenium enolate intermediate to the corresponding carbonyl compound, followed by protonation of the resultant alkoxide with the G-H acidic starting nitrile, hence regenerating the catalyst and releasing the aldol adduct, which can easily dehydrate to afford the desired a,/3-unsaturated nitriles 157 in almost quantitative yields. Another example of this reaction type was reported by Lin and co-workers,352 whereas an application to solid-phase synthesis with polymer-supported nitriles has been published only recently.353... 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

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