Osmium clusters mononuclear

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) ... 

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). 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

Linkage isomerizations, osmium, 37 335-339 Linked cubane clusters, Fe—S proteins, biological implications, 38 55-56 Linked macrocyclic ring systems, 45 75 dinuclear systems, 45 89-95 triaza ring systems, 45 76-87 Li—N—Li linkages, 37 100-101 Lipoxygenase, inhibitors, 36 41 Liquid-liquid extraction of metal ions, 9 1-80 with acidic P-based extractants, 9 34-48 with acidic P-based extractants dinuclear, 9 47-48 mononuclear, 9 34-47 with amines and amine oxides, 9 49-56 complexes in, 9 68-71 countercurrent extraction method, 9 15-25... 

Table X lists examples of clusters in which a p3 group such as Ni(C5H5), Co(C5H5), Rh(C6HsMe), Co(CO)3, Ir(CO)3, Pt(PR3)2, Pt(CO)(PR3), or W(C5H5)(CO)2 caps a triangle of osmium atoms to which it is attached only by metal-metal bonds. Many are made by direct reaction of Os3H2(CO)10 with an appropriate mononuclear precursor, but less systematic routes are clearly also available. Two of the examples are paramagnetic.

Pyrolysis reactions of mononuclear carbonyls and low-nuclearity cluster compounds have been used extensively in the syntheses of HNCC of osmium (54, 72,80,95,108), ruthenium (18,20,29), and, more recently, rhenium (2-4). The reactions have been carried out either in inert solvents or, to facilitate the ejection of CO or other volatile ligands, in the solid state under vacuum. Condensation processes under pyrolytic conditions are rarely specific and, as such, lead to the formation of a wide range of products. In order to obtain optimum yields of a particular HNCC, the reaction conditions must be carefully screened. Solution reactions offer advantages such as the ability to monitor the progress of the reaction using IR spectroscopy. As they often give... 

A series of osmium carbonyl complexes have been prepared by the reaction of OsO-with CO or decomposition of Os3(CO)i2 [226] and a mononuclear homoleptic osmium carbonyl complex, Os(CO)5, is also known. It is a volatile, colorless liquid and is the most robust M(CO)5 type complex of the iron triad against both oxidation and heat but it gradually loses CO to form Os3(CO)i2. Multinuclear osmium carbonyl clusters such as Os3(CO),2, Os5(CO)i6, Os5(CO)i9, Os6(CO)ig, 087(00)2, and OsgfCO).. have also been reported [227]. In this section, several carbonyl complexes based on Os3(CO)j2are described. 

Substituted carbonyl clusters react with halogens in much the same way as their parent carbonyls. The final products of the reaction of halogens with Ru3(CO)9(PPh3)3 are the dimers [Ph3PRu(CO)2X2]2, as detected by Piacenti and co-workers (325, 326), but the initial products are the mononuclear Ph3PRu(CO)3X2 which dimerize with loss of CO just as the Ru(CO)4X2 compounds did (212). No trinuclear products were detected. The corresponding trisubstituted osmium carbonyl cluster... 

Substitution of water molecules by Cl or Br has been reported for the chal-cogenide clusters [Mo3Y7(H20)6j (Y = S, Se). Finally, dirhodium cyclo-pentadienyl derivatives with -OH bridges have been reported. An unusual five-coordinated hydrido-hydroxo mononuclear derivative of osmium is obtained upon reaction of HOsCl(CO)(PPr 3)2 with KOH in methanol. ... 

Thermal decomposition of the grafted cluster (H)Os3(CO)io(OSi ) results in a total destruction of the molecular cluster frame. This destruction probably results from a multiple oxidative addition of silanol groups on 3 metal atoms with formation of (H)Os(CO)3(OSi ) which can be reversibly decarbonylated to HOs(CO)2(OSi ). These mononuclear osmium hydrido species are also catalysts for hydroformylation. 

The early chemistry of hexanuclear carbonyl clusters, including those of ruthenium and osmium, has been reviewed.The hexaruthenium dianion [RuslCOlis] is prepared inside NaX-zeolite cages in 80-90% yields by treatment of [Ru(NH3)6] /NaX with CO and H2. Oxidation of the supported dianion results in cluster degradation to mononuclear ruthenium products, a process that is reversible on re-exposure to CO/H2. A redetermination of the crystal structure of Os6(CO)i8, as its chloroform solvate, confirms the bicapped tetrahedral metal core seen with the unsolvated cluster. 

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