Osmium clusters polynuclear

Several other polynuclear metal carbonyls were tested as catalysts for the reduction of nitrobenzene to aniline using carbon monoxide and water as the reducing agent. Rhodium, iridium and osmium clusters were found to be very effective and they were far less susceptible to oxidative degradation than [Fe(CO)5]. 3... 

A knowledge of these enthalpic terms, and therefore of the relative bond energies, would be expected to considerably clarify many of these fundamental aspects. The data in Table 4 show that, with the main exception of rhenium and osmium, the metal-metal distances in the tetranuclear clusters and in the pure metals are quite similar this relationship is generally valid for all the polynuclear carbonyls60. The metal-metal bond energies in clusters are therefore expected to be of the same order as those in the metallic state for a close-packed arrangement, these are given by the formula Z m-m = A//f M(g)/6. 

The structures of anionic, triple-nuclear osmium and iron cluster catalysts supported on copolymers of styrene and divinylbenzene were analyzed by means of IR spectroscopy. Their catalytic activity during 1-hexene hydroformylation [250] and C5H5NO2 carbonylation [251] were investigated. It was found that isomerization proceeds simultaneously in the presence conventional catalysts. In the absence of moisture, a triple-nuclear osmium complex could be removed from a polymeric support after reaction. This suggests catalytic activity for this complex, particularly in the fixed state. Furthermore, a definite correlation was found to exist between polynuclearity and selectivity of heptanol formation. For iron, however, the cluster structure altered during the course of the reaction. 

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