Cluster compounds osmium

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

Electrochemical investigations of [Au2Re2(H)6(PPh3)6](PF6) have shown that this cluster displays a rich redox chemistry (244) and it has been concluded that the existence of this reversible electron transfer chemistry is due to the considerable amount of Re-Re multiple bond character that is retained in the cluster. A number of gold-osmium cluster compounds have been reported to show reversible redox chemistry (245). 

These metals are prolific formers of clusters, most of which obey the electron counting rules just presented. Osmium forms the greatest number, and is the only one to form clusters with more than six metal atoms. Indeed, osmium cluster compounds are so numerous (including many heteronuclear ones) that they afford examples of many subtle structural variations. 

The formation of carbido-carbonyl cluster compounds with ruthenium and osmium appears to be common in pyrolysis reactions the basic reaction may be viewed as the transformation of the coordinated carbon monoxide to carbide and carbon dioxide. Small variations in... 

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 -... 

Decene complexes with gold, 12 348 Deformation density, 27 29-33 Degradation reactions, heteronuclear gold cluster compounds, 39 336-337 Dehydration reactions, osmium(II), 37 351 Delocalization, see also Valence delocalization added electron, reduced dimer, 38 447, 449 optical centers, interaction with surroundings, 35 380 Density... 

There are families of metal cluster compounds (Fig. 6.40) containing metal clusters surrounded by ligands (Lewis Green, 1982). In small cluster compounds, the electrons are paired, but in large clusters there will be closely spaced electronic levels, as in metal particles. In such clusters, quantum size effects would be expected. Benfield et al (1982) have found intrinsic paramagnetism in H20sio(CO)24 below 70K as expected of an osmium particle of approximate diameter of 10 A the excess paramagnetism increases with cluster size in osmium compounds (Johnson et al, 1985). 

High Nuclearity Carbonyl Cluster Compounds of Osmium 295... 

HIGH NUCLEARITY CARBONYL CLUSTER COMPOUNDS OF OSMIUM... 

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... 

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). 

Metal carbonyl cluster compounds which contain three ruthenium or three osmium atoms in the cluster core are common.1 Potentially useful reagents for syntheses of these compounds are the triruthenium and triosmium dianions [M3(CO)h]2 (M = Ru, Os).2 Therefore, it is desirable to develop good synthetic routes to obtain [M3(CO)11]2- (M = Ru, Os) of high purity in high yields. A method that is particularly useful for generating [M3(CO)n]2 (M = Ru, Os) is the designed stoichiometric reduction of M3(CO)12 (M = Ru, Os) using an electron carrier such as potassium-benzophenone.3... 

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... 

The only apparent exception to this rule is the hydrido-bridged osmium cluster (/u-CHjX/u-H lOsalCOhol (75) (Table IV). The alkanediyl derivatives (type G) may even be distinguished from the closely related metal alkyls. The chemical shifts of the latter compounds typically cover the... 

In their original paper (2) on the structure of Fe5C(CO)l5, Dahl and co-workers assigned two bands in the infrared spectrum of hydrocarbon solutions of the cluster, at 790 and 770 cm-1, to vFeC modes. This assignment has been confirmed by a recent study of the infrared spectra of the series M5C(CO)15, (M = Fe, Ru, Os) (78). The room temperature spectra of the compounds (Table II) in the solid state are quite similar to each other, comprising three bands assigned as the a, and e modes (split in the solid state) expected for the C4 symmetry of the isostructural clusters. At low temperature the ruthenium and osmium clusters exhibit five absorptions associated with M-C stretches, whereas the iron cluster retains its room temperature spectrum. This is ascribed to the presence of two types of cluster molecule in the crystal lattices of the ruthenium and osmium clusters which are isostructural with, but not isomorphous with, the iron analog in which all the molecules are identical. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Au4(PPh3)4()U-SnCl3)2], which has been prepared in these laboratories (195), is isoelectronic and isostructural with the homonuclear gold cluster compound [Au4(PPh3)4(/w-I)2] (269) and has the structure illustrated in Fig. 22b. Both of these clusters exhibit longer Au-Au bonds than are found in the gold-osmium cluster. 

---