Ruthenium carbonyls synthesis

Ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [PBuJBr was reported by Knifton as early as in 1987 [2]. The author described a stabilization of the active ruthenium-carbonyl complex by the ionic medium. An increased catalyst lifetime at low synthesis gas pressures and higher temperatures was observed. 

Figure 1 Synthesis of ruthenium-carbonyl clusters with the 3,5,6-bicyclophosphite-l,2-o-isopropylidene-a-D -glucofuranoside ligand.

Fischer-Tropsch synthesis could be "tailored by the use of iron, cobalt and ruthenium carbonyl complexes deposited on faujasite Y-type zeolite as starting materials for the preparation of catalysts. Short chain hydrocarbons, i.e. in the C-j-Cq range are obtained. It appears that the formation and the stabilization of small metallic aggregates into the zeolite supercage are the prerequisite to induce a chain length limitation in the hydrocondensation of carbon monoxide. However, the control of this selectivity through either a definite particle size of the metal or a shape selectivity of the zeolite is still a matter of speculation. Further work is needed to solve this dilemna. 

Finally, the surface-mediated synthesis of ruthenium carbonyl complexes has also been used to prepare supported ruthenium particles. Using silica as a reaction medium and conventional salts, apart from Ru3(CO)i2, mononuclear Ru(CO)j, and high nuclearity carbonyl-derived species can be obtained by CO reductive carbonylation [127, 128]. This opens new routes to preparing tailored supported ruthenium particles. 

Acetic acid has been generated directly from synthesis gas (CO/H2) in up to 95 wt % selectivity and 97% carbon efficiency using a Ru-Co-I/Bu4PBr "melt" catalyst combination. The critical roles of each of the ruthenium, cobalt and iodide catalyst components in achieving maximum selectivity to HOAc have been identified. Ci Oxygenate formation is observed only in the presence of ruthenium carbonyls [Ru(C0)3l3] is here the dominant species. Controlled quantities of iodide ensure that initially formed MeOH is rapidly converted to the more reactive methyl iodide. Subsequent cobalt-catalyzed carbonylation to acetic acid may be preparatively attractive (>80% selectivity) relative to competing syntheses where the [00(00)4] concentration is optimized that is, where the Co/Ru ratio is >1, the syngas feedstock is rich in 00 and the initial iodide/cobalt ratios are close to unity. 

To achieve, then, high acetic acid selectivity directly from synthesis gas (eq. 1) it is necessary to balance the rates of the two consecutive steps of this preparation - ruthenium-carbonyl catalyzed methanol formation (10) (Figures 2 and 5) and cobalt-carbonyl catalyzed carbonylation to acetic acid (Figure 6) - such that the instantaneous concentration of methanol does not build to the level where competing secondary reactions, particularly methanol homologation (7, H), ester homologation (12, 13), and acid esterification (1 ), become important. 

Ruthenium carbonyl complexes have been shown to catalyze a number of car-bonylation processes. The ruthenium-catalyzed intramolecular Pauson-Khand reaction was found to proceed in the presence of Ru3(CO)12 (Eq. 105) [165,166]. The reaction is a valuable tool for selective organic synthesis. 

Ruthenium carbonyl complexes, for example, Ru3(CO) 12 can be used as catalysts for the synthesis of oligosilazanes via dehydrocoupling of Si-H bonds with H-N bonds (Eq. 117) [185]. 

Recent literature describes the synthesis of vinyl esters in the presence of platinum metal complexes. Complexes which have proven particularly suitable in this context are those of ruthenium (eq. (15)), such as, for example, cyclooc-tadienylruthenium halides [36], ruthenium carbonyl complexes, and ruthenium acetate complexes [37]. A characteristic feature of these is their high selectivity with regard to acetylene, so that the production of acetylene polymers is reduced. 

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... 

It is useful to explore this analogy between known alkyne systems and potential benzyne ones. For example, alkynes react with ruthenium carbonyl to form the Ru4( --alkyne)(CO)i2, which form an octahedral RU4C1 arrangement with the metal atoms in a butterfly geometry. Since the synthesis cannot be adapted to arynes, another method is needed. Oxidative addition of aryl iodides to Ru3(CO)i2 gives the aryl complexes described in Sec. 1.14.4.5. Flowever, we have... 

E3.1 Synthesis and reactivity of sulfido-ruthenium carbonyl clusters... 

For the osmium and ruthenium carbonyl systems, replacement of carbonyl groups by effective leaving groups, such as acetonitrile, has resulted in the development of synthetic procedures leading to the designed synthesis of cluster derivatives. Thus for... 

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