Publisher Summary This chapter focuses on the specific aspect of cluster organometallic chemistry, and describes the synthesis, characterization, structure, and reactivity of transition metal clusters containing alkyne, or alkyne-derived ligands. Alkynes display a diverse reactivity in their reactions with carbonyl clusters, and exhibit a wider range of coordination modes than any other simple, unsaturated molecule. Several factors affect the nature of the products in a reaction between a transition metal cluster and an alkyne or alkene. The chapter presents the various synthetic routes to alkyne or alkene-substituted clusters to analyze the changes in reactivity of the cluster systems when one or more of the important reaction parameters are altered. Tri-, tetra-, and higher nuclearity clusters are discussed separately in the chapter. The chapter presents a brief description of the chemistry of alkylidyne-substituted clusters. The main difference between the reactions of high-nuclearity clusters with alkynes and alkenes and those of the smaller clusters is that the addition of the organic fragment can produce the rupture of metal-metal bonds without cluster breakdown. One of the most important links between alkylidyne and alkyne compounds is that one of the first synthetic routes for cobalt alkylidynes involved alkynes as reagents. Alkyne-substituted cluster compounds are amenable to and, indeed, have been subjected to all of the standard techniques for structural characterization.

Alkyne-Substituted Transition Metal Clusters

Publisher Summary The advances in the field of cluster chemistry in the past few years have been considerable, and although some of the chemistry to be discussed in this review has been the subject of report elsewhere . Many of the principles of structure and reactivity have not been discussed previously. This article is not regarded as a comprehensive account but rather as an assessment of the current views of the cluster compounds. Muetterties has drawn attention to the similarities between the chemistry of transition-metal surfaces and transition-metal clusters and encourage the view that the study of transition-metal clusters would provide information about interactions occurring at the surface of heterogeneous catalysts. The clusters also possess intrinsic novel properties, which suggest that these clusters might serve as potential catalysts for a range of processes. The report at rhodium carbonyl clusters were effective catalysts in the production of ethylene glycol considerably enhanced this view, but there remains the considerable problem of whether the true catalyst in these reactions is a cluster rather than some mononuclear species. Currently, work is in hand at several centers to resolve this dilemma.

Transition-Metal Molecular Clusters

Skeletal Rearrangement of a C2 Unit on a Triruthenium Cluster. Synthesis of μ-Ethylidene, μ3-Ethylidyne, and μ3-Vinylidene Complexes by the Reaction of {Cp*Ru(μ-H)}3(μ3-H)2 with Acetylene

Alumina-supported tetraosmium cluster anions: Precursors of catalysts for isomerization of but-1-ene

The tetranuclear hydrido cluster [Os4(µ-H)4(CO)12]1 has been activated by Me3NO–MeCN to give a reactive intermediate [Os4(µ-H)4(CO)10(MeCN)2]2 which reacts further with cyclohexa-1,3-diene in CH2Cl2 under refluxing to produce new clusters including the benzene-co-ordinated compounds [Os4(µ-H)2(CO)10(η6-C6H6)]5 and [Os4(CO)9(η6-C6H6)(η4-C6H8)]6. Structural analyses of 5 and 6 by X-ray diffraction have shown that the benzene ligand is co-ordinated to one metal atom in an η6 fashion, and the C6H8 ligand in 6 is also terminally bonded to one metal atom. Crystal data: 5, a= 8.209(1), b= 15.029(2), c= 16.453(2)A, β= 89.90(1)° and Z= 4; 6, a= 15.614(2), b= 16.465(2), c= 18.010(2)A, β= 89.42(2)° and Z= 8. Interconversion between compounds 5 and 6 has been observed. Reaction of 5 with cyclohexa-1,3-diene via Me3NO-MeCN activation leads to the formation of 6, while thermal decomposition of 6 affords 5.

Reaction of [Os4(µ-H)4(CO)12] with cyclohexa-1,3-diene via chemical activation: synthesis and structural characterisation of [Os4(µ-H)2(CO)10(η6-C6H6)] and [Os4(CO)9(η6-C6H6)(η4-C6H8)] and their interconversion

The complexes [Os4(CO)11(cyclo-olefin – H)H3](cyclo-olefin = cyclo-octatetraene, cyclo-octa-1,5-diene, cyclo-hexene, or norbornene) have been identified as the products of reaction of [Os4(CO)12H4] with the appropriate cyclic olefin. The structures of these complexes are discussed in terms of available spectroscopic data and in the case of the title complex [Os4(CO)11(C6H9)H3] on the basis of a single-crystal X-ray analysis. This molecule crystallises in space group P21/n with a= 9.266(4), b= 14.850(8), c= 16.847(9)A, β= 93.39(3)°, and Z= 4. The osmium atoms define a tetrahedron, with the cyclohexene ring σ-bonded to one metal and π-bonded to another. The complex [Os4(CO)12H4] also reacts with the acyclic olefins CH2CH2, CH2CHPh, CH2CHCMe3, CH2CMeCMe3, and cis-CHPhCHPh to give the related complexes [Os4(CO)11(olefin – H)H3]. On heating, apart from the complex where the olefin is CH2CMeCMe3, dehydrogenation occurs to produce the dihydrido-complexes [Os4(CO)11(R1CCR2)H2](R1= H, R2= H, Ph, or CMe3; R1= R2= Ph). These complexes have been shown to contain a R1CCR2 fragment bound via two σ and one π bond to one tetrahedral face of the Os4 cluster unit.

Some reactions of dodecacarbonyltetrahydridotetraosmium with olefins; the molecular structure of 1,1,1,2,2,3,3,3,4,4,4-undecacarbonyl-1,2-µ-(1′-σ,1′–2′-η-cyclohexenyl)-tri-µ-hydrido-tetrahedro-tetraosmium

Sharwan K. Rehani

Papers

Some reactions of dodecacarbonyltetrahydridotetraosmium with olefins; the molecular structure of 1,1,1,2,2,3,3,3,4,4,4-undecacarbonyl-1,2-µ-(1′-σ,1′–2′-η-cyclohexenyl)-tri-µ-hydrido-tetrahedro-tetraosmium

Tetranuclear osmium clusters from the reactions of H4 Os4 (CO)12 with alkenes