Osmium clusters

Fig. 4 Osmium clusters supported on MgO(OOl) a OssC/MgisOs and b OS5C at a surface point Vs defect site [33] these were represented by density functional theory, and the samples were characterized by EXAFS spectroscopy, transmission electron microscopy, and other techniques [15]...

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 above reaction is close to being quantitative. Stoichiometry was determined by varying molar ratios of reactants. The Cz Hio was identified by mass spectrometry. In this reaction oxygen is abstracted from Cz H80 (THF) by boron to form the B303 unit. Two hydrogens from BH3 add to the C He unit to form C H10 while the third hydrogen adds to the osmium cluster. 

Scheme 8.2 Mechanism for the hydrogenation of ethylene catalyzed by silica-supported osmium clusters (CO ligands omitted for clarity).

The Osmium cluster Os3(CO)12 and clusters in the presence of various phosphines and triphenylphosphite have been utilized for the hydrogenation of cinnamaldehyde and crotonaldehyde (Table 15.7) [36]. The results show that good yields of unsaturated alcohols can be obtained by using a large excess of phosphine at elevated hydrogenation temperatures. 

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). 

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... 

Fischer-Tropsch catalysis, 34 71, 38 331-335 C2 oxygenate formation, 38 338 oxide-supported osmium clusters, 38 335 product selectivites, 38 333-334 proton-induced reduction of CO, 38 332-333... 

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. 

Scheme 59. Synthesis of silsesquioxane thiol-coordinated ruthenium and osmium clusters.

Scheme 1.4 Catalysis with a silica supported grafted osmium cluster (while keeping the molecular cluster intact).

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 -... 

Figure 5.17 X-ray molecular structure of trimetallic osmium cluster 1. (Reproduced with permissiou from ref. 28.)...

EFFICIENT BASE- AND SILICA-MEDIATED SYNTHESES OF OSMIUM CLUSTER ANIONS FROM - Os(CO)3Cl2 2... 

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 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). 

Only one reaction type leading to heterometallic osmium clusters has been reported (248, 249). Among the products obtained from Os3(CO)j2 and M(C0)5 ... 

Cluster complexes can also be used as starting compounds for the synthesis of heterocarbonyl compounds via ligand replacement. Treatment of [Os3(H)2(CO)9(NMe3)] with S = CPh2 afforded two different osmium clusters depending on the reaction conditions. Each contained a 77 -bound thiobenzophenone ligand.117... 

Os(NH3)5 r 2-(C,0)-acetone) ] [105164-47-4], and benzene adducts, [Os(NH3)5(q2-C6H6)]2+ [107202-74-4] and [Os(NH3)5(C6H6)Os(NH3)5]4+ [107202-75-5] (106,107). The chemistry of osmium clusters is replete with examples of ligands engaged in intimate and unusual bonding modes with multiple metal centers. 

---