Osmium cluster, addition

Reaction (105) could also be induced in benzene at room temperature by addition of silver perchlorate. Of related interest is the decarboxylation of diketene either by an osmium cluster to give an i73-allyIosmium complex [Eq. (106)] (114) or by (T7-C5H5)Mn(CO)2(thf) to give (77-C5H5)-Mn(CO)2(allene) (115). 

Using as catalyst precursors the clusters Os3H2(CO)i0 and Os3(CO)12 [71, 72], Laine and coworkers found a deuteration pattern of quinoline hydrogenation similar to that shown in Scheme 16.16, except for the presence of more deuterium in the 4-position and less in the 2-position, which has been interpreted in terms of the occurrence of oxidative addition of the osmium cluster to C-H bonds in quinoline, and also 1,4-hydrogenation (Scheme 16.17). 

Chemical Properties. Compound 2 is readily decarbonylated upon exposure to UV irradiation.5 Irradiated solutions of 2 readily yield addition products of sulfur containing small molecules such as COS, CS2, and H2S. In the absence of reagents it will form the hexanuclear compound Os6(CO)17(/r4-S)2. It reacts with other metal complexes to form higher nuclearity osmium clusters and heteronuclear metal cluster compounds.5,11,12... 

The osmium cluster, H20s3(CO)io, reacts with DIPCD via addition across the C=N bond of the carbodiimide. ... 

The first p3—if type to be structurally characterized was an osmium cluster anion. Caulton et al.17 reported a rhodium/osmium complex which has the carboxylate carbon bound to osmium and each oxygen bound to different rhodium centers. Cutler et al.24 characterized additional complexes of this type. Few examples exist of the other two structural types. 

Although less fully documented than osmium cluster chemistry, rhenium cluster chemistry has been subjected to many structural studies, including those on approximately 20 neutral or anionic carbonyls, particularly carbonyl hydrides [Rev(CO). H ] of nuclearities x = 2 to 6 (Fig. 7). In addition, some ten or more rhenium carbonyl carbides [Rev(CO)vH C] have been shown to contain a core carbon atom, usually occupying a central octahedral site. These systems offer scope not only to explore for rhenium the trends we have already shown for osmium, but also to study the effect on metal-metal distances (and so enthalpies) of such core carbon atoms, which formally donate all four of their valence shell electrons to the cluster bonding. To our knowledge only one rhenium carbonyl cluster compound, Re2(CO)io, has been subjected to calorimetric study to determine its enthalpy of formation. ... 

So far the discussion has concentrated on the reactions of symmetric 1,3-diynes with trinuclear ruthenium and osmium clusters. Related reactions occur with asymmetric diynes. For example, the reaction of [Ru3(CO)8(/tt-dppm)2] with HC CC CSiMes in thf gives [Ru3(/t-H)(CO)s(/r-dppm)2(/t3-7 --L-C2C GSiMe3)] 263 via the oxidative addition of the terminal C CH component of the diynyl ligand across one of the dppm-bridged Ru-Ru bonds. 

Osmium cluster dianions [Os]7(CO)36] 330 and [Os2o(CO)4o] 331 are formed in up to 10 and 20% yields, respectively, by vacuum pyrolysis of Os3(CO)io(NCMe)2 at temperatures above 260 °C. Complex 330 contains a close-packed arrangement of 16 metal atoms, with the additional Os breaking the otherwise threefold symmetry of the metal core. The two osmium atoms with metal connectivities of 8 and 9 have significantly shorter Os-Os bond distances (2.663 A), comparable to that of the bulk metal (2.6754A). The cluster is electron-precise, with 210 c.v.e. The electron-deficient complex 331 consists of a cubic close-packed arrangement of metal atoms, and has been characterized by IR spectroscopy in five oxidation states. 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

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