Ruthenium carbonyl anion

Homogeneous hydrogenation of carbon dioxide to methanol is catalyzed by ruthenium cluster anions in the presence of halide anions. The catalyst system was Ru3(CO)i2 and alkyl iodides in A -methylpyrrolidone (NMP) solution at 513 K. Some methane was also formed. FT-IR spectra of the reactions allowed identification of several ruthenium carbonyl anions. 

Anions of iron carbonyls form, with few exceptions, the only anionic carbonyl compounds known for this group of metals. One ruthenium carbonyl anion, [C5HsRu(CO)2] , has been investigated. Osmium appears to have been completely neglected in this area of carbonyl chemistry. 

Although this spectrum does not correspond to any particular ruthenium carbonyl complex, it is consistent with the presence of one or more anionic ruthenium carbonyl complexes, perhaps along with neutral species. Work is in progress with a variable path-length, high pressure infrared cell designed by Prof. A. King, to provide better characterization of species actually present under reaction conditions. 

Submitted by MICHAEL 1. BRUCE and MICHAEL L. WILLIAMS Checked by GUY LAVIGNE and TH RESE ARLIGUIEt This tetranuclear ruthenium carbonyl hydride was described on several occasions,5 but early preparations were usually contaminated with Ru3(CO)12, giving rise to suggestions of the existence of two isomeric forms. The situation was clarified by the work of Kaesz and coworkers,6 who discovered the direct route from Ru3(CO)12 and hydrogen, which is described below. The compound is often obtained from reactions between Ru3(CO)12 and substrates containing hydrogen (hydrocarbons, ethers, alcohols, water, etc.) and by acidification of anionic ruthenium cluster carbonyls.7... 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Methanol is protonated to give an ion pair with a ruthenium carbonyl iodide anion. Dehydration by an 5 2 type process gives a methyl complex which undergoes insertion of carbon monoxide to an acetyl intermediate followed by reduction to an alkoxy derivative. Finafly. ethanol is released via hydrogenation of the alkoxy intermediate. 

Mono- and Dinuclear Compounds. The pentacarbonyl is a starting material for mononuclear ruthenium carbonyl complexes. As outlined in Scheme 3, reduction with sodium in liquid ammonia yields a pale-colored anion solution (5),... 

A particularly broad potential for application in syngas reactions is shown by ruthenium carbonyl clusters. Iodide promoters seem to favor ethylene glycol (155,156) the formation of [HRu3(CO),]- and [Ru(CO)3I3]- was observed under the catalytic conditions. These species possibly have a synergistic effect on the catalytic process. Imidazole promoters have been found to increase the catalytic activity for both methanol and ethylene glycol formation (158-160). Quaternary phosphonium salt melts have been used as solvents in these cases the anion [HRu3(CO)u] was detected in the mixture (169). Cobalt iodide as cocatalyst in molten [PBu4]Br directs the catalytic synthesis toward acetic add (163). With... 

Ruthenium carbonyl, Ru3(C0)i2 rather than RuC13 was selected as the metal precursor, with a view to maximising the dispersion and minimising surface contamination by anions. Oxidation-reduction cycles have also been reported to increase dispersion of ruthenium and selectivity to higher hydrocarbons and, in particular, to olefins (4,5). Some preliminary results of our studies are reported here. 

Reductions of ruthenium carbonyls have been studied less. Reduction of Ru3(CO),2 by Na in liquid NH3 yields the [Ru(CO)4] anion, probably in admixture with [RuH(CO)4] -. Acidification of the anion with dilute H3PO4 yields the thermally unstable RuH2(CO)4. The analogous OsH2(CO)4 is a rather thermally stable compound showing that the thermal stability of the MH2(CO)4 complexes increases drastically from Fe and Ru to Os Fe = Ru Os. 

Concentrated aqueous salt solutions were used for dehydration of carbohydrates catalyzed by RuC13 + Ag2S04 ( RuSCV) [47]. Such solvents may also help in constructing aqueous-organic biphasic media with good phase separation properties. Selective dehydroxylation of polyols and sugars was achieved in aqueous solutions with the use of anionic ruthenium carbonyls, as well [48],... 

VpQ, 1886 cm ) plus a series of bands at 1943, 1974, 2004, 2038 and 2052 cm Again we may be seeing more highly nucleated ruthenium carbonyl cluster anions (113). However, both the relative intensity and position of the individual bands in this set do vary as a function of initial catalyst concentration, olefin conversion, etc., suggesting that two or more metal carbonyl species may be in dynamic equilibrium... 

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