Osmium clusters trinuclear

The various modes of bonding that have been observed for alkenes to the trinuclear osmium clusters are shown in Fig. 7 [see (88)]. The simple 77-bonded structure (a) is relatively unstable and readily converts to (c) the vinyl intermediate (b) is obtained by interaction of alkene with H2Os3(CO)10 and also readily converts to (c) on warming. Direct reaction of ethylene with Os3(CO)12 produces (c), which is considered to be formed via the sequence (a) — (b) — (c) and (d). Both isomers (c) and (d) are observed and involve metal-hydrogen and metal-carbon bond formation at the expense of carbon-hydrogen bonds. In the reaction of Os3(CO)12 with C2H4, the complex 112088(00)902112, (c), is formed in preference to (d). Acyclic internal olefins also react with the carbonyl, with isomerization, to yield a structure related to (c). Structure (c) is... 

The most extensive studies of the chemistiy of cluster complexes have been associated with the trinuclear cluster unit, as may be anticipated. A wide range of substitution reactions has been demonstrated for both Ru3(CO)i2 and Os3(CO)i2, with the full range of ligands normally employed in the study of metal carbonyl chemistry. In genera 1, the trinuclear osmium cluster is more readily maintained, ruthenium often giving rise to cluster breakdown, yielding mononuclear and binu-clear adducts. This reflects the increased bond enei of the metal-metal bond on descending the triad (see Table X later in this section). 

Trinuclear osmium clusters have received considerable attention recently. The green isomer of [Os3(//-H)2(CO)9(CNBu )], in contrast to the previously known red isomers, contains the CNBu ligand bonded in an axial site to the Os atom not associated with bridging hydrides. Fluxionality is associated with 3-fold rotation of the carbonyls of the Os(CO)3 units, the hydride ligands and carbonyls of the Os(CO)3(CNBu ) remaining unaffected. In the complex [ (OC)4(Bu NC)Os Os3(CO)u] there is evidence of restricted rotation about one of the Os—Os bonds at... 

Some model reactions on related trinuclear ruthenium clusters, especially related to the reduction reactions of nitrobenzene to aniline, have also been reported by Bhaduri and coworkers and several papers have also been published by different groups on related reactions of ruthenium and osmium clusters containing imido. amido or isocyanate fragments, although the latter were not intended as models for catalytic reactions. 

Bridges between trinuclear metal clusters [of Ru, Os] Synthesis of ruthenium and osmium carbonyl clusters with unsaturated organic rings Oxyligand derivatives of triosmium dodecacarbonyl... 

Photochemical Activation. Coordinative unsaturated fragments may also be produced by photolytic reactions. In presence of UV-irradiation metal carbonyl compounds lose sequentially CO-ligands. Electron-deficient, solvent coordinated species produced in this way may combine with inactivated metal complexes via the formation of donor-acceptor metal-metal bonds. Iron, ruthenium, and osmium trinuclear carbonyl clusters may be prepared by this way ... 

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. 

For trinuclear cluster complexes, open (chain) or closed (cycHc) stmctures are possible. Which cluster depends for the most part on the number of valence electrons, 50 in the former and 48 in the latter. The 48-valence electron complex Os2(CO)22 is observed in the cycHc stmcture (7). The molecule possesses a triangular arrangement of osmium atoms with four terminal CO ligands coordinated in a i j -octahedral array about each osmium atom. The molecule Ru (00) 2 is also cycHc and is isomorphous with the osmium analogue. 

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. 

The [Os3(CO)io( t-H)( t-OSi)]surface catalyzes the isomerization and hydrogenation of olefins. When the hydrogenation of ethylene is carried out at 90 °C the trinuclear framework of the initial cluster remains intact in all the proposed elementary steps of the catalytic cycle [133]. However, at higher reaction temperatures the stability of the [Os3(CO)io( t-H)( t-OSi)]sujface depends on the nature of the reactant molecule. It is moderately active in the isomerization of 1-butene at 115 °C but decomposes under reaction conditions to form surface oxidized osmium species that have a higher activity [134]. 

Penta- and hexanuclear clusters of the metals osmium and ruthenium coordinate with the same r ri ri - binding mode as the trinuclear clusters to CgQ. Such complexes are known for the clusters OsjC [75,76], RU5C [77-79], RugC [78], PtRu5C [77] and Rhg [80], In this collection of metal clusters rhenium plays a special role, because it forms a new fullerene-metal sandwich complex, where two C50 are bound to one cluster. 

Some four-electron capping units enter as such. This is the case for the many reactions forming/t3-sulfur ligands from elemental sulfur (103). It also holds for the triruthenium /i3-nitrene cluster 45, formed from Me3SiN3 and Ru3(CO)i2 (104). A versatile four-electron ligand is the acetylene moiety, which can add facially to M3 units as a two-center capping group, as found in the clusters 46, which can be obtained from trinuclear carbonyls of iron, ruthenium, and osmium (105, 106). 

NLO properties, 12, 771 from oxygenated ligands, 6, 842 with palladium, 8, 213 and Rh Cp complexes, 7, 160 trinuclear clusters, overview, 6, 835-871 Osmium complexes... 

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