Ruthenium carbonyl clusters cobalt

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... 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

The choice of catalyst can have a significant effect on these ratios. For reaction 26.5, a cobalt carbonyl catalyst (e.g. HCo(CO)4) gives a 80% C4-aldehyde, 10% C4-alcohol and 10% other products, and an h ratio 3 1. For the same reaction, various rhodium catalysts with phosphine cocatalysts can give an n i ratio of between 8 1 and 16 1, whereas ruthenium cluster catalysts show a high chemo-selectivity to aldehydes with the regioselectivity depending on the choice of cluster, e.g. for Ru3(CO)i2, a 2 1, and for [HRu3(CO)ii], 74 1. Where the hydroformylation... 

Many metal clusters are air-stable compounds. However those of the first transition metal series are in general more sensitive to air. Thus, binary carbonyl of ruthenium, rhodium, and iridium are rather air-stable species while those of iron, Fe3(CO)i2, and cobalt, Co4(CO)i2, rapidly decompose apparently via formation of the carbonates. 

---