Cobalt-ruthenium system

Jeimer G (1988) Hydrocarbonylation of linear and branched aliphatic C2-C4 alcohols catalyzed by cobalt-ruthenium systems. A comparative study. J Organomet Chem 346(2) 237-251... 

DR. SUTIN The cobalt systems that you mention differ from the iron and ruthenium systems I discussed in that the electron transfer is also accompanied by a spin change the cobalt(III) complexes are low-spin and the cobalt(II) complexes are high-spin. Thus, the electron transfer is spin forbidden and should not occur since =0. It becomes allowed through... 

Monometallic ruthenium, bimetallic cobalt-ruthenium and rhodium-ruthenium catalysts coupled with iodide promoters have been recognized as the most active and selective systems for the hydrogenation steps of homologation processes (carbonylation + hydrogenation) of oxygenated substrates alcohols, ethers, esters and carboxylic acids (1,2). 

The activity of this ruthenium system is comparable to, or somewhat greater than, that of cobalt catalysts under the same conditions of temperature and pressure. Rhodium catalysts provide substantially higher activity than either of these systems. As will be seen later, however, addition of ionic promoters can greatly increase the activity of ruthenium-based catalysts. 

The observation of glycerol triacetate as a trace product of CO hydrogenation by this ruthenium system in acetic acid solvent (179) suggests that glycolaldehyde (ester) can undergo further chain growth by the process outlined in (26) for the cobalt system. As with formaldehyde, however, a carboxylic acid is apparently necessary to promote formation of the metal-carbon bonded intermediate which can produce the longer-chain product. 

A mechanism possibly involving intermolecular hydride transfer in this promoted ruthenium system is thus very different from the reaction pathways presented for the cobalt and unpromoted ruthenium catalysts, where the evidence supports an intramolecular hydrogen atom transfer in the formyl-producing step. Nevertheless, reactions following this step could be similar in all of these systems, since the observed products are essentially the same. Thus, a chain growth process through aldehyde intermediates, as outlined earlier, may apply to this ruthenium system also. 

The use of cobalt/ruthenium catalyst systems giving high ethanol yields has been claimed in patents by Commercial Solvents (39), British Petroleum (40], Exxon (411, Gulf [42], Rhonc-Poulcnc (43], and Union Carbide [44]. Usually... 

The hydrogenolysis to thiols can be carried out effectively in a biphasic system, with the catalyst exclusively soluble in the polar phase, thus enabling easy catalyst recycling. However, to introduce this biphasic technique to industrial hydrodesulfurization, much research has to be carried out to design catalysts that are suitable for biphasic catalysis and that contain inexpensive metals (cobalt, ruthenium). Furthermore the catalysts have to tolerate the great thermal and chemical stress of the reaction conditions. 

The activity increases asymptotically as a function of the electroless bath time in the case of the nanostructured films. In contrast, the planar films show a lower catalytic activity. This may arise due to an inefficient cobalt deposition. The hydrogen release rate is comparable to the values found with platinum and ruthenium systems [104]. 

They also observed that the reaction of Ru(NH3)j(mbpy) and C02 " produces no detectable radical intermediate and attributed this to fast intramolecular electron transfer (k > 10 s ). The difference in reactivity of the cobalt and ruthenium systems was suggested to be due to the fact that both the acceptor and donor orbitals are of n symmetry for the ruthenium system while the acceptor orbital is of a symmetry in the cobalt system. 

An account of a method for the homologation of methyl esters, catalysed by a ruthenium-cobalt bimetallic system, may have some future synthetic potential. Six- and seven-membered heterocyclic enamino-esters (74) undergo ring-contraction to give five- and six-membered azacyclic esters (75) in 89-92% yield (Scheme 40). The reactions of dianions derived from carboxylic acids and esters have been reviewed. ... 

IH of alkynylamines has been performed with a variety of catalytic systems based on palladium [274-281], cobalt, rhodium, iridium, ruthenium, platinum, copper, silver, zinc, cadmium, mercury [279-281], nickel [279-282], gold [279-281, 283], and molybdenum [284] derivatives. 

Second, as a logical development of the first approach, polyphosphazenes have been synthesized that bear phosphine units connected to aryloxy side groups (37). The phosphine units bind organometallic compounds, such as those of iron, cobalt, osmium, or ruthenium (38). In several cases, the catalytic activity of the metal is retained in the macromolecular system (39). A similar binding of transition metals has been accomplished through nido carboranyl units linked to a polyphosphazene chain (40). 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

CO Subsequently a migratory insertion will take place. Oxidative addition of H2 will be faster at the electron rich metal centre and thus the aldehyde will form. Hydrogenation takes place at ruthenium (added as Ru3(CO)i2) as indeed catalyst systems containing cobalt only are known to give 3-hydroxypropanal as the product. 

In a more detailed examination of the ruthenium-cobalt-iodide "melt" catalyst system, we have followed the generation of acetic acid and its acetate esters as a function of catalyst composition and certain operating parameters, and examined the spectral properties of these reaction products, particularly with regard to the presence of identifiable metal carbonyl species. 

---