Cobalt metal carbonyl clusters

HOs6(CO)18] and H2Os6(CO)18 marks one of the highlights of the early period of osmium carbonyl cluster chemistry [162]. While both the dianionic cluster and the monoanionic system have the expected octahedral metal core, a capped square based pyramidal structure was found for H2Os6(CO)18. This turned out to be the archetypal example for the capping rule , a concept which proved to be very successful in the analysis of the structures of metal carbonyl clusters of the iron and cobalt triads [166],... 

A few review articles on carbaboranes have appeared during the year, including those on cobalt carbaboranes, structure and property modification of m-carbaborane siloxanes, and further electron counting correlations between boron clusters and metal carbonyl clusters. ... 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

Co-MCM-41 catalyst in H2 at temperatures up to 993 K. It is this intermediate species that preserves the tetrahedral environment in the silica framework and provides the resistance to complete reduction to the metal in the presence of H2. The Co(II) species is resistant to reduction in pure CO the intermediate Co(I) species is more reactive in CO, likely forming cobalt carbonyl-like compounds with high mobility in the MCM-41. These mobile species are the precursors of the metal clusters that grow the carbon nanotubes. Controlling the rates of each step of this two-step reduction process is a key to controlling the sizes of the cobalt metal clusters formed in the cobalt MCM-41 catalysts. 

In those catalysts, the metal species were deposited in the form of salts or carbonyl clusters. Further, the modifications of the oxide surface with the multinuclear cobalt carbonyl cluster Co3(CO)9—CR (R = CH3 or Ph) have been reported (68). 

Another similarity between HCo(CO)4 and HRh(CO)4 is that they are only stable under certain reaction conditions. Unlike HCo(CO)4, HRh(CO)4 does not usually precipitate out as metallic rhodium, but rather forms stable rhodium carbonyl clusters such as Rli4(CO)i2 and Rh6(CO)i6- Indeed, just as Co2(CO)g is a common catalyst precursor for cobalt hydroformylation, Rh4(CO)i2 is often used as a starting species for rhodium hydroformylation. 

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

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