Alkyne-Substituted Transition Metal Clusters

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.