Clusters of Ruthenium and Osmium

The lowest nuclearity carbidocarbonyl clusters of ruthenium and osmium are RujC(CO)1J( 10, andOs5C(CO),s, 11. The former is synthesized in high yield by the carbonylation of Ru6C(CO),7 (see below) under precisely determined conditions of temperature and pressure [Eq. (9)] (29). 

The osmium analog was obtained in moderate yield by pyrolysis of Os CO) or Os3(CO),2 (20). Both the ruthenium (29) and osmium clusters (31) are isostructural with the original iron analog, 1 (2), the metal atoms describing a square pyramid, each vertex bearing three terminal carbonyls. The carbon atom lies fractionally below the center of the basal plane of the cluster, protruding 0.11 A below the Ru4 plane in 10 and 0.12 A below the Os4 plane in 11 [cf. a value of 0.08 A for Fe5C(CO)15 (2)] (see Fig. 11). 

The structure of the triphenylphosphine substitution product is known (29). The square pyramidal Ru6C core is retained, and the phosphine replaces one carbon monoxide from a basal Ru(CO)3 group in 10. The carbide carbon atom is situated 0.19 A below the square face of the pyramid (cf. 0.11 A in 10). 

Heating 10 under argon regenerates Ru6C(CO)l7, and reaction with hydrogen yields a hydride cluster tentatively identified as H2Ru5C(CO),5 

Both 10 and 11 react with halide ions to give [M5C(CO),5X] products. The iodopentaosmium cluster [Os5C(CO)I5I], 12, has been fully characterized by X-ray diffraction (Fig. 12) and adopts an open arachno structure based on a pentagonal bipyramid but lacking two equatorial vertices (31). 

---

Tri- and tetranuclear ferrocenyl-acetylene clusters of ruthenium and osmium are described in Ref. 473. 

It seems that one of the future developments in cluster chemistry lies in the production of nanosized particles (1 nm = 10 A) with well defined stoichiometries, which can be used as catalysts or as catalyst precursors. In this context, high nuclearity mixed-metal clusters are particularly useful because two or more metal atoms with different chemical properties can be combined in the same unit. The Cambridge group has spent the last few years designing rational synthetic routes to mixed-metal high nuclearity clusters of ruthenium and osmium with the coinage elements, which produce cluster cores of up to one nanometer in size. ... 

Since the completion of this review (mid-1982), the chemistry of carbidocarbonyl clusters has continued to expand rapidly. The task of the reviewer is made even more difficult as fascinating results continue to appear. In resisting the temptation to make a comprehensive update of the field, it would be remiss of me not to direct the reader s attention to the continued investigations of Lewis, Johnson, and co-workers in the chemistry of ruthenium and osmium carbidocarbonyls (89), the report by Longoni and coworkers (90) of the syntheses of the first nickel carbide clusters and some mixed nickel-cobalt carbides, the syntheses by Shapley of a new ruthenium dicarbide cluster [Ru,oC2(CO)24]- (91) and of Os6C(CO)l7 (92), and the work of Shriver which implies the existence of a very reactive tri-iron carbide cluster (93). 

Reduction of Ru3(CO)i2 and Os3(CO)i2 with sodium in ether solvents at various reaction temperatures has been found to provide an effective route to HNCC of ruthenium and osmium 382). Although most of the dianions produced by this method had been isolated previously, the study of these reactions has allowed a better understanding of the build-up processes of these clusters. 

Reactions of ruthenium and osmium cluster carbonyls with heteroatom-substituted and functionalized alkynes (metallocycles) 00IZV1. 

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. 

E3.5 Molecular and crystal structures of ruthenium and osmium arene clusters... 

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

Norton JR, Colhnan JP et al (1972) Preparation and structure of ruthenium and osmium nitrosyl carbonyl clusters containing double-nitrosyl bridges. Inorg Chem 11 382-388... 

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

As with previous publications (GOMG (1982) and GOMG (1995)), phosphorus ligands feature heavily in the chemistry of ruthenium and osmium. In many instances the focus of the publications is such that the phosphorus-containing species are peripheral to the specific reactivity that a publication might be dealing with. For this reason, phosphorus ligands are somewhat ubiquitous within cluster chemistry. Here, an attempt has been made to focus on the phosphorus and its interaction with the cluster. 

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. 

Ruthenium-copper and osmium-copper clusters (21) are of particular interest because the components are immiscible in the bulk (32). Studies of the chemisorption and catalytic properties of the clusters suggested a structure in which the copper was present on the surface of the ruthenium or osmium (23,24). The clusters were dispersed on a silica carrier (21). They were prepared by wetting the silica with an aqueous solution of ruthenium and copper, or osmium and copper, salts. After a drying step, the metal salts on the silica were reduced to form the bimetallic clusters. The reduction was accomplished by heating the material in a stream of hydrogen. 

The results of the EXAFS studies on osmium-copper clusters lead to conclusions similar to those derived for ruthenium-copper clusters. That is, an osmium-copper cluster Is viewed as a central core of osmium atoms with the copper present at the surface. The results of the EXAFS investigations have provided excellent support for the conclusions deduced earlier (21,23,24) from studies of the chemisorption and catalytic properties of the clusters. Although copper is immiscible with both ruthenium and osmium in the bulk, it exhibits significant interaction with either metal at an interface. 

The ruthenium-copper and osmium-copper systems represent extreme cases in view of the very limited miscibility of either ruthenium or osmium with copper. It may also be noted that the crystal structure of ruthenium or osmium is different from that of copper, the former metals possessing the hep structure and the latter the fee structure. A system which is less extreme in these respects is the rhodium-copper system, since the components both possess the face centered cubic structure and also exhibit at least some miscibility at conditions of interest in catalysis. Recent EXAFS results from our group on rhodium-copper clusters (14) are similar to the earlier results on ruthenium-copper ( ) and osmium-copper (12) clusters, in that the rhodium atoms are coordinated predominantly to other rhodium atoms while the copper atoms are coordinated extensively to both copper and rhodium atoms. Also, we conclude that the copper concentrates in the surface of rhodium-copper clusters, as in the case of the ruthenium-copper and osmium-copper clusters. 

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 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... 

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

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. 

MIXED-METAL CLUSTERS OF IRIDIUM WITH RUTHENIUM AND OSMIUM... 

Mixed-Metal Clusters of Iridium with Ruthenium and Osmium 207... 

---