Osmium complexes clusters

On strongly basic oxides such as MgO, osmium cluster complexes are converted irrespective of their nuclearity to mononuclear Os carbonyls bound to Mg " on MgO at higher temperatures (above 200°C). Under CO -I- H2 at 473 K, a mixture of H30s4(C0)i2 and OsioC(CO)24 is regenerated (64), which is active for the methanation reaction (Fig. 18) ... 

Homogeneous hydrogenation of Q to THQ is also catalyzed by Os3(CO)j2 and its derivatives. These studies, together with the synthesis of osmium cluster complexes of quinoline, have led to another mechanism for quinoline hydrogenation which involves more than one metal center. It is likely that reactions catalyzed by Cp Rh(NCMe)3 and Os3(CO)i2 proceed by different mechanisms. Whether either of these mechanisms is consistent with the heterogeneously catalyzed conversion of Q to THQ is unknown. 

Some pentanuclear osmium cluster complexes show structures with edge-bridged tetrahedral geometries (c in Fig. 2.17). These structures have the same number of metal-metal bonds as the square-based pyramid but only triangular faces, so the stabilization of intersticial atoms is not possible there. 

Many reports on ruthenium and osmium cluster complexes are mainly concerned with structural features. These are covered elsewhere in this Volume so only those reports dealing with syntheses and reactions are mentioned here. 

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. 

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. 

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). 

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... 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

Few examples are known for this type of intramolecular dihydrogen bond. One of them is the trimetallic osmium cluster shown in Structure 5.15 [28]. This compound, described well by various methods, has revealed a number of problems connected with characterizations of dihydrogen-bonded complexes that deserve separate discussion. The hydrogen atoms localized in the x-ray molecular structure of complex 1 of Figure 5.17 provide a formulation of interaction N-H -... 

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... 

MIXED-METAL CLUSTER COMPLEXES OF NICKEL WITH RUTHENIUM OR WITH OSMIUM... 

The substitution reactions can be accompanied by subsequent reactions. Thus, Ru3(C0)i2 reacts with azobenzene (61) or fluorinated azobenzenes (60) to yield products like [47], and the pyrolysis of Ru3(CO)9L3 complexes leads to reactions similar to those discussed in Chapter 3.4. for the corresponding osmium clusters. Rearrangements and orthometalations were observed (65, 66), and one cluster formulated as [42] was isolated (65). 

Terminal acetylenes and Ru3(CO)j2 yield complexes of the type [57] (9,190, 336), whereas internal acetylenes form either complexes [56] or acetylene-substituted RU4 complexes (229). Alternatively, two acetylene moieties are incorporated with formation of metallacyclopentadienes (229), a class of compounds more familiar in osmium cluster chemistry (cf. Chapter 3.4.). Instead of two acetylene molecules, one molecule of an arylbutadiene may be the precursor of the metallacycle (382). 

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